Walnuts for theNortheast

Edward Goodell

The walnut has been held in high esteemsince ancient times. The Romans consideredit preeminent among nuts and gave it thename jovis glans (Jupiter’s nut), from whichthe modem taxonomic name for the walnut

genus, juglans, has been derived. Severalspecies of walnuts are popular throughoutthe Western World today, both for their finewood and flavorful nuts. Large commercialwalnut industries exist in the Mediterranean

region of Europe and on the west coast ofthe United States (primarily California, with200,000 acres). Although walnuts are grownthroughout much of this country, they havenever been grown widely in the Northeast.Several types can be grown here, however,including the Persian walnut ( juglans regiaL.), the black walnut (J. nigra L./, the butter-nut (f. cinerea L.~, and the Asian walnuts (J.ailanthifolia Carr, j. mandshurica Maxim.,and j. cathayensis Dode), all of which havenutritiou6, flavorful nuts. We will explore inthe following the merits of these types andtheir cultivation in the northeastern UnitedStates and adjoining areas of Canada.Any talk of walnuts must begin by ad-

dressing the toxic effect walnuts are said toexert on neighboring plants. Pliny the Elder,in the first century A.D., wrote, "the shadow

Black walnuts / Juglans nigra/ ripening on thetree. Al Bussewitz photo.

of walnut trees is poison to all plants withinits compass...." While it is true that walnutspecies (and some hickories) produce a toxicchemical identified as juglone (5-hydroxy-l,4-napthoquinone) the actual phytotoxic ef-fect varies considerably depending on / 1 ~ thedifferent levels of tolerance among plants, (2)whether or not the roots of adjacent plantscontact the walnut root, and (3) the amountof air present in the soil. Although the blackwalnut probably has the most notoriousreputation for allelopathy (as destructivechemical interaction between plants isknown), this phenomenon has been increas-ingly documented throughout the plantworld, and it is worth noting that tall fescuegrass (Festuca arundinacea Schreb.) exertsa similar deleterious effect on walnuts (Riet-veld 1981/. ( .Toxic juglone is oxidized from hydroju-

glone, a nontoxic substance found in allparts of the walnut plant. Oxidation ofhydrojuglone occurs in the presence of airand during contact between walnut rootsand the roots of other plants that containoxidizing compounds. Hydrojuglone ishighly reactive, however, and in the con-tinued presence of air quickly breaks downinto harmless substances. Root-to-root con-tact is therefore the only means by whichdamage can occur unless plants are in soilthat is poorly drained, and therefore poorlyaerated.

Tomatoes, apples, most ericaceous plants,

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and many conifers are known to be adverselyaffected (MacDaniels 1976 and 1980). The ef-fects of walnut toxicity are noticeable eitheras flagging, wilted leaves (in tomatoes) ormore commonly as a long-term gradualstunting of the plant. On the other hand,many plants are not affected at all, includingnumerous grasses and vegetable crops, manylegumes, some Rosa and Vitis species, andmost native hardwoods. This immunity mayresult from either a root zone that does notcoincide with that of the deep-rooting wal-nut or an actual tolerance to the toxic prop-erties of juglone.According to current information we can

be optimistic about the prospects of success-fully growing a wide range of plants in as-sociation with walnuts. A general precau-tion is advised: locate susceptible plantswith a long life span outside the eventualroot zone of walnuts. This is urged espe-cially in wet soils, where the toxic effect ismore likely. However, during the initial pe-riod of growth walnuts can be grown neareven susceptible plants (as root spread is nar-row and contact therefore avoided). For ex-ample, at an orchard spacing of 6 meters on-center black walnut can be interplantedwith vegetable crops, small fruit, and/orChristmas trees for at least 10 years.

Persian Walnut

The common commercial walnut is thePersian walnut, fuglans regia. This was theonly walnut known to the Ancient Romans.juglans regia came to Rome from Persia viaGreece, and Roman conquerors spread itthroughout southern Europe to England.On the North American continent Juglans

regia is often called the English walnut, pre-sumably because it was introduced here byEnglish colonists. However, it is not grownextensively in England. Most horticul-turalists call it the Persian walnut in defer-ence to its origin.The Persian walnut is native to the area

between the Carpathian Mountains in east-ern Europe and the Himalayan Mountains innorthern India, a swath across the BalkanPeninsula, Turkey, Iran, Afghanistan, andthe adjoining areas of the USSR. A geograph-ically disjunct population occurs in northernChina (Icongraphia CormophytorumSinicorum 1972 and Meyer 1911). Wildplants are normally found in mixed broad-leaf forests, along stream banks, in valleys,and on mountain slopes (Komarov 1936). Insheltered valleys, where it thrives, Juglansregia may grow 20-35 m high with astraight, upright trunk and a large, spreadingcrown. Normally the wood is purplishbrown, hard, and satin-smooth and shinywhen polished. The nuts of wild trees gener-ally have thin shells and large kernels. Vari-ous subspecies have been proposed based onnut shape, growth habit, and geographic ori-gin (Komarov 1936 and Rehder 1940).Persian walnuts have always been valued

trees within their native and naturalized

range. The timber is used in Europe for finewoodwork and veneer. Trees that are suc-cessful in the northeastern United Stateshave come from colder regions of thespecies’ range, Romania, Hungary, Czecho-slovakia, Poland, USSR, and Germany, wherethey have traditionally been popular yardtrees. Outstanding selections are currentlybeing propagated and tested for commercialorchards in these countries (Shreve 1981 /.Most selections of Persian walnuts cold

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Carpathian walnuts, /Juglans regia) above, origi-nated m the Carpathian Mountams of southernPoland.

hardy enough for North America derive fromseed collected in the Carpathian Mountainsof southern Poland. Reverend Paul Crath, anative of the Ukraine, worked as a Presbyte-rian missionary in that region between 1924and 1936, after having been ordained aminister in Canada. Reverend Crath was

keenly interested in the Juglans regia treeshe found commonly growing in Poland,where minimum winter temperatures couldreach -40°F. He believed that some of thesetrees would succeed in cold areas of NorthAmerica. Through arrangements withmembers of the Northern Nut Growers’ As-sociation and the Wisconsin Horticultural

Society, he sent back several tons of seed(Devitt 1953). The resulting trees, often

called Carpathian walnut trees and knownfor their cold hardiness, became widely es-tablished from British Columbia to NovaScotia and are still being selected for theirhardiness, nut qualities, and yields.Reverend Crath’s introductions were not

the first cold-hardy Persian walnuts broughtto North America, however. Since the late1700s German immigrants had been bring-ing hardy Juglans regia seed from theirhomeland to Pennsylvania and farther west.The descendants of these seedlings are onthe average less tolerant of cold than the

Carpathian walnuts, but several are amongthe most hardy and productive cultivars.Other promising introductions have beenmade from the Russian Ukraine, theHimalayan Mountains, and northern China.A great deal of potential still exists for col-lecting genetically superior seed from the

6 1

cold-temperate areas where the Persian wal-nut has been grown since antiquity.

In a 1936 letter Reverend Crath describedthe trees of the Carpathian region:We examined 79 walnut trees in and around Cos-seev. The age of the trees varied from 15-100

years. Trees 30 years old and over were from 60 to75 feet tall, and from I to 3 feet in diameter. Ofthe 79 trees, only 3 trees were damaged by thefrost of 1929 (45 degrees below zero) (Rahmlov1962).

Experience on this continent has shown thatwith good site conditions a cold-hardy Per-sian walnut tree will rapidly grow to the sizeand shape of a very large apple tree. Thecanopy is globe shaped and dense, the barkpale gray, and the roots deep. When fullydormant, some Persian walnuts may toleratetemperatures between 30°F and 40°F with-out damage (O’Rourke 1969). ).However, injury can occur at much

higher temperatures ( -13°F) if mildweather precedes a drop in temperature. Per-sian walnuts will grow on a variety of soils,but poor drainage invariably renders themmore susceptible to winter injury. Highvigor and good nut production require a fer-tile, nearly neutral soil and room for exten-sive root development.

Persian walnuts are monoecious. Thestaminate catkins expand from lateral budsof the previous season’s growth. The clustersof 1-3 (occasionally 4-5) pistillate flowersare borne at the tips of the current season’sshoots. Pistillate flowers, and the nuts thatsubsequently develop from them, normallyappear only on growth originating from theterminal buds. On some cultivars the lateralshoots also bear flowers, which increasestheir yield. It is unclear as to whether allPersian walnut trees are self-fertile or not

(personal communication from L. H. Wil-moth, July 21, 1982). Regardless, the overlapin staminate and pistillate flowering timeswould rarely be enough to ensure a goodcrop. Several cultivars are notable for their

self-fruitfulness, but even these seem tobenefit significantly from cross-pollinationwith another cultivar.

In the North the most common cause of

crop damage among Persian walnuts is theirtendency to produce leaves and flowers be-fore the possibility of late frosts has passed.In Ontario, Persian walnuts are most suc-cessful within 20 km of the Great Lakes,where the cool spring climate delays vegeta-tive growth. The gradual onset of winterthere also ensures a more complete dor-mancy and less damage from cold. Under op-timal growing conditions Persian walnutseedlings bear fruit within 4-8 years andgrafted cultivars within 2-5 years. A fewseedlings from a Russian source have beenreported to flower in their second year(McDaniel 1978). Pistillate flowers are gen-erally produced several years before stami-nate flowers. In their eighth growing season,productive cultivars may bear 0.03-0.06 m3of nuts. Large trees may yield 0.2 m3 (Grimo1979). Reverend Crath reported harvests of45-115 kg from mature, native Carpathiantrees. Persian walnuts bear crops annually,though weather conditions have a consider-able effect on yields. Individual trees areknown to continue bearing for more than100 years.

Juglans regia is unique among walnuts inthat its nuts fall free from the husks at ripen-ing time. This feature, combined with easilycracked shells, places Persian walnutsamong the more desirable of nuts. The ker-nels can usually be extracted in large or

7

whole pieces from the relatively thin-shellednuts by hand. The kernels are high in protein(20 percent) and fat (60 percent) and accountfor 40-60 percent of the total nut weight.On the west coast of this country, Persian

walnut trees are valued for their appearanceand are grown in yards, parks, and alongstreets. In the cold areas of eastern Europeand northern China, they have long beenvalued for their nuts and timber also. Now,however, selections hardy in the northeast-ern United States offer nuts and timber of a

quality similar to that of the European andChinese types.

Growing Persian Walnuts

Many Persian walnut growers in the Northare cultivating the seedlings of superior treesin the hope of finding improved types. Plantsgrow readily from seeds sown in the fall, orafter a relatively short (6-8 weeks) artificialcold-moist treatment. They will also germi-nate satisfactorily after dry storage if theyare first soaked for several days in cleanwater that is changed daily. Spring plantingis best, about 4 cm deep with a light mulch.Cans or wire mesh placed over the seeds willprotect them from rodents, crows, andpheasants.

Planting sites for Persian walnuts must bechosen carefully. Adequate soil drainage isimportant, as moist soil delays the onset ofwinter dormancy, causing freeze damage(splitting) to the trunk. The soil must allowdeep roots to penetrate 1.5 m, have an ap-proximately neutral pH (pH 7) and be fertileenough to grow a good cover crop. Addingdolomitic lime or fertilizer, or planting alegume in the preceding year is recom-mended to improve the soil.

A single Persian walnut tree will eventu-ally occupy a space 15 m in diameter but canbe planted at half that spacing to hasten or-chard production. Seedlings may be grown tobearing age for evaluation on only 3-meterspacings. Seedlings of good parentage arelikely to yield one tree in ten "exceptionalenough to be made permanent" (Society ofOntario Nut Growers). The hole to whichthe seedling is transplanted must be largerthan the spread of the root system. A kilo-gram of bonemeal mixed into the plantingsoil (preferably one year in advance) is a re-quirement for healthy growth. Any injuredroots must be trimmed off before planting,and the remaining roots carefully spreadwhen the soil is sifted over them. It is best to

place the root collar at, or slightly below,ground level. When the seedling is in place,the soil must be tamped down and wateredthoroughly. A trunk guard, or a piece ofwoven wire coated with white latex paint,will protect against sunscald and rodents.The young tree will not be able to competewith weeds and will respond favorably tomulch as it grows.

Persian walnuts must not be fertilized inthe first year, and only in the early springthereafter. These trees use large amounts ofnitrogen and phosphorus: one recommenda-tion is 0.2 kg of 20-10-10 granular fertilizerper 3 cm of trunk diameter until the trunkdiameter reaches 15 cm. After that the ap-plication rate is doubled, up to a maximumof 11-13 kg per tree with a 5-10-15 formula-tion. This tends to reduce vegetative growthand increase nut production.Pruning requirements are minimal. Many

Persian walnuts independently exhibit theideal conical or dome shape, requiring onlythe removal of branches that are dead, rub-

8

bing, or malformed. A high, clear trunk canbe maintained for lumber production.

Persian walnuts grown in the Northeastare potentially susceptible to several pestsand diseases (Payne and Johnson 1979), in-cluding the husk fly, the coddling moth, thebutternut curculio (insect larva), an an-thracnose fungus, a bacterial blight, and abunch disease (which causes numerousshoots to emerge in close proximity). Choos-ing disease-resistant plants, removing leavesfrom beneath the trees after leaf fall, andtiming sprays carefully will provide success-ful control. Trees exhibiting a bunching pat-tern in the branches should be removed en-

tirely, as should trees that sucker exces-sively from the lower trunk. The latter is anindication of either bunch disease, walnutblight, a genetic lack of hardiness, or wetsoil.

During the ripening period, squirrelspoach nuts before they have fallen, but asmooth trunk collar (0.5 m high) will keepthem out of the treetops as long as no accessis provided by an adjoining tree or building.Even so, the nuts must be harvested fre-

quently if squirrel populations are dense inthe immediate area.Treatment after the harvest involves dry-

ing the walnuts in an airy location for aboutfive days. During this period the kernel losesits milky texture, becoming crisp and sweet.Like most foods, walnuts sold commerciallydo not compare in taste to those grown athome. Storing walnuts is best accomplishedeither in-shell, using rodent-proof aeratedcontainers in an unheated room, or by freez-ing the kernels alone. Nuts with well-sealedshells usually retain their kernel qualityuntil the next harvest season. Frozen kernelswill store for years with very little change inquality.

Persian walnuts have much to recom-mend them. They are attractive landscapetrees, having pale bark and a dense, roundcrown. Several cultivars are hardy at averageminimum temperatures as low as -30°F ifsoil and air drainage are adequate.

Black Walnut

The black walnut is a native American

tree that grows wild throughout easternNorth America except most of New Yorkand New England. It is among the most val-ued cabinet-wood and veneer trees on thiscontinent. A commercial cracking industryin the Midwest is supported by wild col-lected nuts. The nuts are valued for theirflavorful kernels and their shells, which areused in the manufacture of a multitude ofuseful products.

Soil conditions are a major influence onthe growth of black walnuts. These trees dobest on soils that have a neutral pH, are fer-

tile, and have adequate water. They growslowly on wet lands, shallow topsoils, andthose that are acidic and infertile. Saplingblack walnuts are intolerant of shade and are

generally suited to sites where white ash~Flaxinus americana grows well (Fowells1965).While truly wild black walnuts are un-

common east of the lower Hudson River

Valley, they have often been planted as yardtrees and sometimes have becomenaturalized.The black walnut tree is large and

straight-trunked, with an open spreadingcrown. The pale green pinnately compoundleaves cast a dappled shade. An identifyingcharacteristic during the dormant season isthe stout, upright branchlets. These resem-

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Black walnuts /~uglans nigra) /

ble the branches of white ash, but the wal-nut branch arrangement is alternate insteadof opposite. Black walnuts normally havedeep tap roots, which when establishedpermit them to coexist with groundcoversand allow them to tolerate some degree ofdrought. These trees are also tolerant of fireand smog (Duke). Their growth rate is highlydependent on site and soil conditions andgenetics; 1 m per year in height is possible.The ornamental value of the black walnut

tree lies in its stately form and the dappledshade it affords. The leaves fall relativelyearly without spectacular coloration. Thedecaying husks leave an amber stain onhands, clothing, and concrete. Black walnuttrees with an unbranched trunk at least 3 m

high will produce both timber and nut crops.

Nuts can be harvested until the lower sec-tion reaches prime veneer log size (55 cm). ).Trunk diameters of orchard-grown trees canbe twice that of similarly aged trees grown intimber plantations, presumably because thesuperior care and the wider spacing of thetrees in orchards are more favorable for girthincrease. Careful pruning is required in theearly years to produce a straight log free oflarge knots.The black walnut, the preferred commer-

cial walnut, has a distinctive flavor, which isnot diminished by cooking. The kernels con-tain approximately 20 percent protein, 15 5percent carbohydrate, and 60 percent fat, aswell as small amounts of mineral nutrientsand vitamins A and B.

Unfortunately, obtaining this nutritiousnut meat can be a frustrating experience. Infact, removing the nut from its messy, stain-

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ing husk and then extracting the kernel fromits hard shell is hardly worth the effort withmost unselected black walnuts. This is notthe case with several cultivars selected fortheir ease of cracking.Cracking qualities depend on shell thick-

ness and the internal shell structure. Thekernel cavities of most unselected blackwalnuts have many partitions and deep in-vaginations, whereas those of named cul-tivars usually have fewer, and kernels can beextracted in large pieces. Also, the nuts ofcultivars are usually 25 percent kernel, 5percent more than the average for unselected

seedlings.Grafted cultivars may begin bearing nuts

within two or three years, though substan-tial production must wait until trees are past10 years of age. Crop yield is more closelycorrelated with crown size and trunk diame-ter than age. A vigorous tree is the best in-surance of a plentiful nut crop. The biggestchallenge in managing walnut trees for nutproduction is to maintain regular annualyields. Even the annual variation in yield isirregular. Providing adequate sunlight, nu-trition, and water and controlling pestsminimizes yield variations but does notnecessarily eliminate them.Black walnut cultivars have been selected

primarily for ease of cracking and productiv-ity. Very little information is available ontheir performance in New England, how-ever. Although over 500 cultivar selectionshave been identified by the Northern NutGrowers’ Association, most have not beenwidely propagated or tested. The perfor-mance reports that do exist vary consid-

erably, depending on climatic, cultural, andsite factors. Observations in New York,Michigan, and Ontario offer the best indica-

tion of desirable cultivars for New England.The most important characteristic for this

region is a capacity to ripen nuts in growingseasons of less than 180 days. Those thathave generally received high ratings whengrown in northern latitudes are listed on

page 16.

Growing Black Walnuts

Black walnut seeds and seedlings arewidely available from commercial and statenurseries. In fact, enough are sold each yearto establish about 2880 hectares of planta-tions (Funk 1979). Seedling trees rarely equalcultivars in nut quality or productivity. Ahomeowner desirous of a single tree is betteroff purchasing a grafted cultivar. For largerplantings, seedlings are more cost-effective,and some may turn out to have improvedcharacteristics for the Northeast. Seeds or

seedlings should be obtained from parenttrees with desirable traits: climatic adapta-tion, superior productivity and nut quality,and perhaps timber form. A large, well-fillednut produces a larger seedling. Cold strat-ification for 120 days results in the mostprompt germination. Fall planting usuallysatisfies this cold requirement. Seeds sownin fall tend to germinate more quickly and ingreater numbers than those sown in spring.The hulls need not be removed before plant-ing the nuts. About 50 percent of unhulledseed will germinate. A higher germinationrate can be achieved by hulling the nuts,placing them in a container of water, anddiscarding those that float. A well-filled nutwill sink if the float test is given before ap-preciable drying has occurred (within 3 daysof hulling).Black walnuts are planted in the same way

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as Persian walnuts. The results of a study ofvarious methods used to protect the nutsfrom squirrels favored placing fresh cowmanure over sown seeds as an "effective,biodegradeable repellent" (Williams andFunk 1978). Due to the fact that they germi-nate in relatively low numbers, black wal-nuts should be seeded at approximatelytwice the desired density. Planting nuts10 cm apart produces tall, straight seedlingsthat are easy to graft or transplant. It is ad-visable to plant several seeds wherever atree is desired. Later (anytime within threegrowing seasons), all of the surviving seed-lings must be removed except the one show-ing the best vigor and form.

In general, direct seeding is better thantransplanting. Black walnuts develop a deeptaproot quickly, which is often damagedin transplanting and is a setback forthe entire tree. After three to four years,trees in a plantation tend to be about thesame size regardless of whether they weregrown from seed or transplanted (Funk1979).A wide hole with room for the roots to

spread is best. Many labor-saving plantingmethods have been devised for transplantinglarge amounts of black walnuts, but theprimary consideration is to ensure that theroots are spiraling. The survival and growthof transplanted seedlings is directly relatedto their size. Only year-old seedlings with astem diameter greater than 5 mm should be

planted.It is important to provide favorable condi-

tions for young black walnut trees. Treesthat are vigorous when young are usuallyvigorous when older also. The most criticalfactors affecting growth rate are soil mois-ture, weed competition, wind exposure, and,

to a lesser extent, nitrogen supply. Weedsshould be controlled with mulch for at leasttwo years (preferably three or four) afterplanting.

Favorable soil conditions are crucial for

healthy growth and nut production. The soilmust be well drained. It should allow rootsto penetrate at least 1.5 m. A near neutral pHshould be maintained with dolomite appli-cations. Trees bearing nuts have high nitro-gen and phosphorus requirements. About 0.5 5kg of 10-10-10 fertilizer per centimeter oftrunk diameter is recommended for ade-

quate nutrition.Another way of improving the soil’s fertil-

ity is to interplant black walnuts withnitrogen-fixing plants. Russian olive .

(Elaeagnus umbellata), black locust ^

(Robinia pseudoacacia European alder (AI-nus glutinosa), and hairy vetch (Vicia vil-losa) have all proved to enhance black wal-nut’s growth rate, especially on less thanideal sites (Funk 1979 and Ponder 1981). ( .These fast-growing nitrogen-fixing speciesshelter the young walnuts from wind and re-duce weed competition somewhat. Addi-tionally, the walnut growth is forced up-ward, which reduces pruning requirements.The general pruning recommendation for

black walnuts is to maintain a single domi-nant leader and evenly spaced lateralbranches. The bottom section of trunk canbe developed as a valuable veneer log bypruning the branches when they reach 3 cmin diameter. Pruning can be done up to halfof the tree’s total height without adverselyaffecting the growth rate. This method keepsthe knots small and confined to the centralcore of the veneer log. Bey (1979) providesfurther information on pruning for timberproduction. Planting black walnuts in frost

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pockets increases the need for pruning, be-cause the terminal buds are more likely tosuffer freeze damage, resulting in manycompeting lateral shoots.To my knowledge black walnuts growing

in eastern Massachusetts have not been

seriously afflicted with diseases or insects.Husk-fly maggots frequently infest the huskin early fall, turning it into a mass of blackslime, but a study has shown no correlationbetween husk maggots and nutmeat quality(Gibson and Kearby 1976). However, somepests can affect nut production (Payne andJohnson 1979). Walnut curculios can damagetender growth and cause some nut loss. Re-moving infected nuts that drop prematurelyis the best control. Anthracnose fungus in-fections of foliage and fruit cause nuts to fillpoorly. Wet weather conditions mean moresevere infections. Anthracnose-resistantcultivars will retain healthy foliage longerand produce better crops. Fungicide spraysduring spring provide successful control.Apparently, black walnuts can be infectedwith walnut bunch disease without showingthe normal brooming symptoms. Instead, itappears as empty or dark and shriveled nuts.There are no reliable controls for this dis-ease. Infected trees should be destroyed.The entire husk and enclosed nut fall

during or shortly after leaf fall. The nuts thatfall early are less likely to be well filled.Freshly fallen nuts are the best ones to col-lect. At this stage the hulls separate easilyand the kernels have not had time to becomestained and lose flavor. Rubber gloves (notvinyl) will protect hands from the corrosive,staining juices. The hull of a freshly har-vested, well-filled black walnut will shuckoff with one tap of a rubber mallet. Thehulled nuts can then be washed, and driedeither on newspaper or in a wire basket for

about one week. The dry nuts are best ifstored in a cool, airy location, and rodent-proof containers are advisable.

Cracking by hand is usually done with ahammer or screw vise. Pouring hot waterover the nuts and allowing them to steep 24hours helps to soften the shells, which pre-vents then from shattering when cracked.The wire cutters used by electricians can beemployed to extract the kernels. Kernels fro-zen in plastic bags keep well.

The Butternut

The butternut, another native Americantree, has a more northerly geographicdistribution than its cousin the blackwalnut. The butternut range occupies muchof New England and the St. Lawrence RiverValley of Quebec, west to southernMinnesota, and south to Missouri andsouthern Appalachia. But rarely is it morethan an occasional component of foreststands. Butternut occurs primarily onstream banks or valley slopes where the soilis moist but well drained. However, it isknown to grow better than black walnut on

dry, rocky soils, especially those oflimestone origin (Fowells 1965).The butternut tree is short, averaging 13 m

high. Thick branches generally begin lowon the trunk and rise into a broad, opencrown. Butternut bark is light brown or grayand becomes deeply ridged with old age. Thecompound leaves resemble those of blackwalnut but are quite hairy and sticky incomparison. The same rust-colored, stickypubescence also covers leaf petioles andyoung branchlets in their first year’s growthand is especially noticeable on the nuthusks. Another identifying characteristic isthe leaf scar. In black walnut it is notched

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Butternuts ~Juglans cmerea) (

without a downy fringe, whereas in butter-nut the leaf scar is not notched but does havea downy fringe.Butternuts are among the most hardy Jug-

lans species, surviving -40°F within theirnatural geographic range. In spring brightgreen staminate catkins droop from thebasal portion of the previous season’sgrowth. The 5-8 pistillate flowers are borneon spikes at the end of new growth. Thesingle or clustered 5- 7 cm egg-shaped nutsripen in early fall. A thin adhering husk en-closes the deeply ridged, thick shell. Thekernels, which are sweet and oily, are gener-ally regarded as the best among walnuts forflavor but are normally impossible to extractin large pieces. A few cultivars exist, se-lected primarily for their ease of kernel ex-

traction and nut size. Cold storage is advis-

able, but nuts in shell reportedly keep a yearor more under cool, ventilated conditions(personal communication from StephenBreyer, July 15, 1982).Nut production begins within six or seven

years from seed (McDaniel 1979), but butter-nuts never seem to yield as well as blackwalnuts. Six bushels of nuts in hull is an ex-

ceptionally high yield from a mature tree,and large annual variations in yield are to beexpected. Butternuts may produce nuts formore than 70 years.Native Americans extracted oil from

crushed butternuts by boiling them in water.In New England the flavorful kernels arestill combined with maple sugar in candy.Like that of the sugar maple tree, the sap ofbutternut also makes a good syrup, but moreboiling is required to thicken it. The husks

14 4

and inner bark yield a true dye. During theCivil War, the backwoods Confederate

troops were sometimes dressed in homespun’uniforms’ of butternut-dyed cloth, and theybecame known as butternuts (Peattie 1966).Butternut wood accepts a high polish and

is easily worked. It was once a favorite forcarriage interiors, because of its combina-tion of beauty and lightness, and is still val-ued. In Wisconsin, one of the major statessupplying butternut lumber, it is secondonly to black walnut for its economic value.The wood is also rot resistant.

Relative to other nut trees, butternuts are

quite short-lived, beginning to decline in 75years. This inherent trait is compounded bysusceptibility to two fungal diseases: thebutternut dieback (Melanconis juglandis~ andthe butternut canker (Sirococcus clavigig-nenti juglandaceareum/. These factors,along with pollution and elimination ofhabitat, threaten the butternut throughoutmuch of its range.

In the colder regions of northeasternNorth America, growing butternuts may bethe only way to harvest high-quality nuts.Cultivars are available with nuts that can becracked easily and flavorful kernels that canbe removed in large pieces. These trees arefast growing with broad canopies offeringdappled shade.

The Asian Walnuts

Three walnut species are native to east Asia:the Japanese walnut / J. ailanthi folia Carr),the Manchurian walnut /J. mandshuricaMaxim.), and the Chinese walnut (J.cathayensis Dode). These are closely relatedto the American butternut and are often in-

cluded in the same subsection of Juglans.

However, the modern authority on the wal-nut family, W. E. Manning (1978) places theAsian walnuts in a separate subsection onthe basis of their differences in embryo de-velopment. In the field Asian walnuts cansupposedly be distinguished from the but-ternut by their notched leaf scars, but thedifference is not readily discernible. Asianwalnuts bear nuts in hanging racemes thatare usually much longer than butternutclusters. The Asian walnuts cross readilywith other juglans species, and fertile hy-brids may result, especially in crosses in-volving the butternut.

Confusion exists about the correct scien-tific name for the Japanese walnut and itssmooth-shelled variety called the heartnut(Rehder 1945). The name formerly acceptedfor the Japanese walnut, J. sieboldiana a(Maxim.), can no longer be used because ithas already been given to a fossil plant. Thecurrent consensus, with which Manningconcurs, is to name the Japanese walnut J.ailanthi folia Carr and the heartnut J. ailan-thifolia var. cordiformis (Maxim.) Rehd.The Japanese walnut is a common forest

tree of mountain regions in Japan (Sargent1894), whereas the heartnut is a cultivatedvariety (Ohwi 1965). The two are identical inhabit and foliage, differing only in nutcharacteristics. The Japanese walnut isrough and pitted like a butternut. Theheartnut is smooth, heart-shaped, and val-ued for its ease of cracking and kernel ex-traction. Seedlings of both Japanese walnutand heartnut may produce either type of nut.The Manchurian walnut is native to

northern China, Korea, and the Amur Riverregion of Siberia. It may grow to 20 m tall,either in mixed forests (in valleys andfloodplains) or isolated on the gravelly soils

15

beside mountain streams. Its growth habitand racemes of 6-17 nuts are similar tothose of the other Asian walnuts. The nuts

vary in shell structure, are round to elon-

gate, 2.7-5.5 cm in length, and (like butter-nuts) have a sharply ridged to relativelysmooth shell. The Manchurian walnut is ex-

tremely hardy, on a par with the butternut.It is cultivated in cold areas of the USSR,Europe, and the Canadian plains. No nut-producing selections have been made in thiscountry. The Lithuanian magazine MusuSodai in 1976 reported a selection hardy to-40°F that blooms first on old wood and

again in 2-3 weeks on new growth (personalcommunication from Victor Vircau on July19, 1982).The Chinese walnut is a close relative and

perhaps only a geographic race of the Man-churian walnut. It grows in the highlands ofcentral China and is considered less hardy.Mature plants at the Arnold Arboretum sur-vive temperatures as low as -10°F without

noticeable damage.Because of its ease in cracking, the

heartnut ( J. ailanthi folia var. cordiformishas received the most attention among theAsian walnuts. In its native Japan it is culti-vated in orchards and marketed. Heartnut

tre.es grow rapidly (to 6 m in eight years) andbear nuts at five years of age. They report-edly adapt to a wide range of soils, from sandto clay, and some will grow in zone 4 (avg.min. temp. -30°F) (Metcalf 1980). However,heartnuts seem to be adapted to a maritimeclimate similar to Japan’s, because they suf-fer damage from early fall freezes and latespring frosts.With the exception of certain cultivars,

heartnuts are said to bear nuts freely butrarely heavily. Gellatly (1966) reported a

Heartnut /juglans ailanthifolia var. cordiformis) (

90 kg harvest from the cultivar called ’OK’.Five to 15 nuts occur in pendant racemes. Arecently ripened soft husk may be twistedoff by hand, leaving only a few fibers at-tached to the shell. Even if the nuts are nothusked immediately, the kernels are less aptto be stained than are those of black wal-nuts.

Heartnuts usually have well-sealed shellsand good keeping qualities. They can gener-ally be split into two heart-shaped halveseither by tapping the shells while holdingthe nuts on edge or by using a channel-locktool. A certain degree of drying can enhancethe cracking process. The kernels have amild flavor similar to that of the butternutbut not quite as highly regarded. The kernelsare about 50 percent oil and 25-35 percent ofthe total nut weight.The heartnut and butternut apparently

cross-pollinate readily, resulting in a fertileand remarkably vigorous hybrid known asthe buartnut ~J. cinerea x j. ailanthifolia var.cordiformis). Several selections combine thehardiness and flavor of butternuts with theease of cracking and potentially greateryields of heartnuts. Two different cultivarsare needed for pollination and subsequentnut production.

In the Asian walnuts and their hybrids, wehave nut-producing, ornamental shade trees

16

for the North. Several features give them anoverall exotic appearance: long hanging cat-kins ; large, compound, seemingly tropicalfoliage; and pendant strings of nuts. Thestout branches and broad top provide a dap-pled shade. Asian walnuts thrive on a varietyof soils. Most are hardy thoughout zone 5and some in zone 4. The primary diseasethreat to these walnuts is the bunch disease.

Walnut Cultivars

A considerable number of commercial nurs-eries supply walnut cultivars. Many ofthem are quite small, however, and managedon a part-time basis. As their stock may besmall or sold out, it is best to place ordersone-half year or more before spring planting.Nurseries usually sell scionwood for do-it-yourself propagation, and some offer custompropagation services.Walnuts are considered difficult to propa-

gate vegetatively. The most common meansis by grafting. Among the most successfulmethods are: a modified side-graft, 75-80percent (Funk 79); a root cleft-graft, 75 per-cent (Groenwald 1981) ; and greenwood bud-ding, 90 percent (Davie and Davie 1977). Ihave used the sprouted-seed grafting methoddescribed for chestnuts (Jaynes 1980) withfair results. A warm post-graft environmentwill enhance the success of all graftingmethods. Heartnuts and Persian walnuts canbe layered (Gellatly 1966 and personalcommunication from Stephen Breyer, July 5,1982), and both rooted cuttings (Shreve1975) and root cuttings of black walnut haveproved successful ~Jaciw and Larsson 1980). ( .Purchasing walnut cultivars is the best routefor most people.

Persian Walnut

The following descriptions are drawnprimarily from those of Ashworth (1969), ),Brooks and Olmo (1972), and Grimo (1979). ).With the exception of ’Hansen’, which ishighly acclaimed, little agreement exists asto how they should be ranked.

’Broadview’ originated in British Colum-bia from seed brought there by a Russianimmigrant from the Black Sea region. Opin-ions differ about its kernel flavor. The nuts,which are medium to large, ripen in Sep-tember at about the same time as McIntosh

apples. In cracking quality they approxi-mately equal those of ’Franquette’, the stan-dard commercial walnut cultivar in Califor-nia. The nuts are 46 percent kernel and keepwell in storage. ’Broadview’ is consideredone of the most productive cultivars. Theoriginal tree withstood temperatures as lowas -30°F, but subsequent reports indicatemarginal hardiness in zone 5.

’Hansen’ is probably the most favored,cold-hardy Persian walnut cultivar. It wasintroduced in 1952 from northwestern Ohio.The original tree may be over 100 years oldand presumably is of German origin. ’Han-sen’ has the ability to fruit on lateral as wellas terminal shoots, resulting in early (2 yearsafter grafting) and numerous nuts. The treesremain small and are resistant to disease andhusk maggots. The nuts mature early andare relatively small but at 60 percent haveone of the highest percentages of kernel. Theround shells are thin and smooth. The ker-nal flavor is mild and sweet. ’Hansen’ is an-other self-fertile cultivar.

’Holton’ is a promising cross between’Hansen’ and ’Broadview’. Preliminary ob-servations indicate that it combines the best

qualities of both parents. Like ’Hansen’ it is

17 7

a hardy and a precocious bearer of nicelyshaped and flavored nuts, which resist dam-age from husk maggots. The ’Broadview’

parentage is evident in the vigor of the treeand its relatively large nuts.

’McKinster’ is a Crath seedling originatingform the Columbus, Ohio, area. The nuts arelarge (48 percent kernel) and have a goodflavor. This fairly productive cultivar, whichself-pollinates, is well adapted to Ohio andfavored in the lower peninsula of Michigan.

’Somers’ is a Crath seedling from the samesource as ’Greenhaven’. ’Somers’ consis-

tently bears attractive high-quality nuts.The kernel usually constitutes more than 55percent of the nut, and its oil content ismore than 64 percent. The early ripening of’Somers’ (early to mid-September) often pre-cedes husk-maggot damage.

Black Walnut

Over 500 black walnut cultivars have beenselected and named. The following areamong those that have received high ratingswhen grown in northern locations. The de-

scriptions are compiled from reports byBrooks and Olmo (1972), Funk (1979), Mac-Daniels (1974 and 1941), and Zanger (1969).

’Sparrow’, from Illinois, has a very thinhull, which is easy to remove. It cracks welland has a high kernel content (29 percent)and very good flavor. Its anthracnose-resistant foliage is retained late into the fall.The nuts ripen fairly early and vary in sizeaccording to site conditions.’Emma K’, from Illinois, has a thin shell, a

high kernel content, and excellent flavor. Itbears nuts regularly in southern Ontario butmay not fill all of them. It appears to be re-sistant to both anthracnose and aphids.

Other cultivars that have received highrating for northern areas are ’Bums’,’Snyder’, and ’Thomas’. Less-tested blackwalnuts with potential value for New En-gland include: ’Beck’, ’Sparks # 127’, ’Sparks# 147’, and ’Davidson’. The latter three havebeen selected in Iowa for their ability toflower on lateral as well as terminal shoots.

(This characteristic leads to earlier andheavier yields.)

Butternut

Butternuts tend to be difficult to propagateand are not in high demand, so nurseriesmay not have stock on hand. A few of thebetter-known and available cultivars are:

’Ayers’, ’Booth’, ’Chamberlin’, ’Craxezy’,’Creighton’, ’Joy’, ’Kinnyglen’, ’Kenworthy’,’Love’, ’Van Sickle’, and ’Weschcke’. All of "

these are reported to be cold hardy in the ’

North.

Heartnut t

Most heartnut cultivars were selected

primarily before attention was diverted tothe introduction of Carpathian walnuts. Thefollowing cultivars are most likely to beavailable. The descriptions follow Campbell( 1981 Gellatly (1966), and McDaniel (1979). ).’Brock’ is a relatively recent and promisingcultivar from Pennsylvania. ’Etter’, alsofrom Pennsylvania, has excellent crackingqualities and is 33 percent kernel. It may beresistant to bunch disease. ’Etter’ seedlingsare often equal to or superior to their parent.’Fodermaier’ nuts are 37 percent kernel but

rarely crack in whole pieces. Even so, it is ahighly regarded heartnut. ’Fodermaier’ seed-lings generally produce good quality nuts.

18 8

’Marvel’ and ’Rival’ are both progeny of’Fodermaier’. Other heartnuts of value in-

clude ’Canoka’, ’OK’, ’Rhodes’, ’Schubert’,and ’Wright’.

Buartnut

I was not able to discover any nurseries thatoffer grafted buartnut trees. The followingcultivars may be available as scions or bycustom propagation: ’Corsan’, ’Dunoka’,’Fioka’, ’Hancock’, ’Leslie’, ’Mitchell’, and’Wallich’.

References

Ashworth, Fred L. 1969. "Butternuts, Siebold (Japanese)Walnuts, and Their Hybrids." In Handbook ofNorth Amencan Nut Trees, edited by R. A.Jaynes. Hamden, Connecticut: Northern NutGrowers’ Associauon.

Bey, C. F. 1979. "Prumng." In Nut Culture in NorthAmerica, edited by R. A. Jaynes Hamden, Con-necticut : Northern Nut Growers’ Association.

Brooks, R., and H. Olmo 1972. Register of New Fruitand Nut Vameues. 2nd edition. Berkeley: Uni-versity of California Press.

Campbell, R. D. 1981. "Ten Years of Expenence withNut Trees." 72nd Annual Report of the NorthernNutGrowers’Associauon 152-54.

Davie, B., and L. Davie. 1977. "Budding Persians, BlackWalnuts, Heartnuts, and Butternuts on BlackWalnut Rootstocks." 68th Annual Report of theNorthern Nut Growers’ Association. 108-110.

Devitt, L. K. 1953. "Late Rev. Paul C. Crath." 44th An-nual Report of the Northern Nut Growers’ As-sociation. 80-84.

Duke, J. A. "/uglans mgra L." Economic Botany Labora-tory, U.S. Department of Agnculture, Beltsville,Maryland, n.d.

Fowells, H. A. 1965. Silmcs of Forest Trees of the U.S.USDA Handbook 271. Washington, D.C.: U.S.Government Printing Office.

Funk, D. T. 1979. "Black Walnuts for Nuts andTimber." In Nut Tree Culture in North America,

’

edited by R. A. Jaynes. Hamden, Connecticut:Northern Nut Growers’ Association.

Gellatly, J. V. 1966. "Heartnuts." 57th Annual Reportof the Northern Nut Growers’ Assoczauon:103-111.

Gibson, K E , and W H. Kearby. 1976. "Black WalnutMeat Quality in Relation to the Presence of HuskFly Maggots in the Husks." 67th Annual Reportof the Northern Nut Growers’ Associatzon.109-13.

Gnmo, E. 1979."Carpathian (Persian) Walnuts." InNutTree Culture in North Amerzca, edited by R. A.Jaynes. Hamden, Connecticut. Northern NutGrowers’ Assoczauon.

Groenwald, M. R. 1981. "Use of Walnut Cleft Graft toProduce Walnut Trees for Nebraska Plantings." "

72nd Annual Report of the Northern Nut Grow-ers’Assoczatzom 62-67.

Iconographza Cormophytorum Sinicorum 1972. Pek-ing. In Chinese.

Jaciw, P., and H. C Larsson. 1980. "Vegetative Propa-gation of Black Walnut." 71 st Annual Report ofthe Northern Nut Growers’ Assoczatzon: 70-74.

Jaynes, R. A. 1980. "Chip Budding Sprouted ChestnutSeed." 7Ist Annual Report of the Northern NutGrowers’ Assoczauon

Komarov, Vladimir L. 1936. Flora of the U.S.S.R. Lenin-grad : Botamcal Institute of the Academy of Sci-ences of the USSR (Available from NationalTechmcal Information Servzce, U.S. Departmentof Commerce, Springfield, VA 22151./ .(

MacDamels, L. H. 1980. "Further Observations on theToxicity of Black Walnut on Tomatoes and SomeOther Plants." 71 st Annual Report of the North-ern Nut Growers’ Assoczauow 112-26.. 1976. "Walnut Toxicity: An Unsolved Prob-

lem." 67th Annual Report of the Northern NutGrowers’ Assoczauon. 114-22.. 1974. "Black Walnut Testing." 65th Annual

Report of the Northern Nut Gzowers’ Assocza-tzon: 68-71.

. 1941. "Nut Growing in the NortheasternStates."Arnoldia, 1: 45-64.

MacDaniels, L. H., W. T. Johnson, and E. J. Braun. 1975."The Black Walnut Bunch Disease Syndrome." "

66th Annual Report of the Northern Nut Grow-ezs’Assoczauon~ 71-87.

McDamel, J. C. 1979. "Other Walnuts, Includzr.g But-temut, Heartnut, and Hybrids." InNut Tree Cul-ture in North America, edited by R. A. Jaynes.Hamden, Connecticut: Northern Nut Growers’Assoczatzon.

. 1978. "Amateur." Nutshell, 32(2) 6-10.Manning, W. E. 1978. "The Classification Within Ju-

glandaceae. Annoys of the Missouri Botanical

19

Garden, 65: 1058-87.Metcalfe, R. E. 1980. "A Three-Year Heartnut Study." "

71st Annual Report of The Northern Nut Grow-ers’ Associatiom 50-52.

Meyer, F. N. 1911. "Agricultural Explorations m the.

Fruit and Nut Orchards of Chma. U. S. Depart-ment of Agnculture Bureau of Plant IndustryBulletm 204 Washington, D.C.: U.S. Depart-ment of Agriculture.

Ohwi, Jisaburo. 19G5. Flora of Japan. Edited by Fred-enck G. Meyer and Egbert H. Walker. Washing-ton, D.C.: Smithsoman Institution.

O’Rourke, F. L. S. 1969. "The Carpathian (Persian) Wal-nut." In Handbook of North Amencan NutTrees, edited by R. A. Jaynes. Knoxville, Tennes-see : Northern Nut Growers’ Association.

Payne, J. A., and W. T. Johnson. 1979. "Plant Pests." InNut Tree Culture m North Amemca, edited byR. A. Jaynes. Hamden, Connecticut: NorthernNut Growers’ Association.

Peattie, Donald Culross. 1966. A Natural History ofTrees. 2nd edition. Boston: Houghton Mifflin.

Ponder, F. 1981. "Some Guidelines for Selecting BlackWalnut Planting Sites." 72nd Annual Report ofthe Northern Nut Growers’ Association: 112-19.

Rahmlow, H. J. 1962. "Distribution of Carpathian Wal-nuts by the Wisconsin Horticultural Society." "

55th Annual Report of the Northern Nut Grow-ers’Association 125-28.

Rehder, Alfred. 1945. "Notes on Some Cultivated Treesand Shrubs, II." Journal of the Arnold Ar-boretum, 26:472.. 1940. Manual of Cultivated Trees and Shrubs.

New York: Macmillan.

Rietveld, W. J. 1981. "Significance of Allelopathy inBlack Walnut Cultural Systems." 72nd AnnualReport of the Northern Nut Growers’ Associa-tion : 117-34.

Sargent, Chailes Sprague. 1894. Forest Flora of Japan.Boston: Houghton Mifflin.

Shreve, L. W. 1981. "Walnut and Almond ImprovementPrograms in Romania and Hungary." 72nd An-nual Report of the Northern Nut Growers’ As-sociation: 22-26.

. 1975. "Black Walnut Propagation TechniquesUsed in the Tree Improvement Programs at Kan-sas State University." 66th Annual Report of theNorthern Nut Growers’Association: 148-55.

Society of Ontario Nut Growers. "Persian Walnuts." "

Newsletter of the Society of Ontario Nut Grow-ers. Niagara-on-the-Lake, Ontario, Canada: Soci-ety of Ontario Nut Growers, n.d.

Williams, Robert D., and David T. Funk. 1978. "CowMa;aure Deters Rodents from Stealmg SeededBlack Walnut." 69th Annual Report of theNorthern Nut Growers’ Association: 43--48.

Zanger, T. G. 1969. "Black Walnuts As Nut Trees." InHandbook of North Amencan Nut Trees, editedby R. A. Jaynes. Knoxville, Tennessee: NorthernNut Growers’ Association.

Edward Goodell is a frequent contributor to Amoldia.