ANR-1125

A L A B A M A A & M A N D A U B U R N U N I V E R S I T I E S

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Greenhouse Productionof Marigolds

Marigolds have longbeen popular withAmerican gardenersas one of the pre-

miere summer annuals. They per-form well in dry, hot, sunny loca-tions and produce dark-green,fine-textured foliage and bright-colored flowers throughout thesummer and into the fall. Theremay be more sizes, flower types,and growth habits of marigoldsthan of any other bedding plant.

Marigolds range in size from 6inches to over 3 feet tall. Dwarfcultivars are appropriate to use incontainers, as bedding plants, oras flower bed borders, while tallercultivars can be used as bedfillers, at the rear of the border, oras cut flowers. In the past, mari-golds had a strong fragrance thatsome people found objectionable.Newer cultivars are somewhatless pungent, but they still havethe characteristic marigold smell.

CultivarsTwo different species of

marigold are commonly grown:African marigolds (Tagetes erecta)and French marigolds (Tagetespatula). Interestingly, neitherAfrican nor French marigoldscome from Africa or France—both species are native to NewMexico and Arizona and south-ward to Argentina. Crosses be-tween African and French mari-golds have resulted in triploidcultivars; therefore, the three

major horticultural types are theAfrican type, the French type, andthe triploid type.

Breeders have worked exten-sively to create cultivars in a widerange of colors, plant sizes, andflower forms. Marigold flowersare available in single, semidou-ble, or double petal arrangementswith white, yellow to orange,gold, or red flowers. Red andcrimson flower colors are foundin the triploid and French typesbut not in the African type.Flower sizes range from 1 inch inthe French type to 5 inches in theAfrican type.

African TypeCultivars of Tagetes erecta,

sometimes referred to as Ameri-can marigolds, are larger plantsthan the French type, often withfewer, larger double flowers. Inthe double-flowered cultivars,there are crested doubles, whoseflowers are mounded and full,and anemone doubles whoseflowers are flat and wide with arecessed center.

French TypeCultivars of Tagetes patula are

usually smaller than African typeplants. Most are 6 to 8 inches, butsome cultivars reach 12 inches inheight. Though double flowerpetal arrangements are available,single and semidouble are morecommon. The single-floweringcultivars stand up to rain and hu-midity better in the South thandouble-flowered cultivars do.

Triploid TypeTriploid cultivars are breeding

crosses between Tagetes erectaand Tagetes patula. One advan-tage of these cultivars is that theyprovide the longest overall dis-play of color in the landscape,often lasting through the hot sum-mer weather into August andSeptember. However, seed germi-nation during production may beconsiderably slower than for theAfrican and French types. Theseplants are sterile, so they will notproduce viable seed.

Best-PerformingCultivars

The Alabama AgriculturalExperiment Station has estab-lished a trial garden at the E.V.Smith Research Center nearShorter, Alabama, to evaluate an-nual garden plants. FourteenAfrican cultivars and 25 Frenchcultivars were visually rated bi-monthly on a scale of 0 (dead) to5 (superior plants in flower) forgarden performance during thesummer of 1997. The 10 best-per-forming African and French culti-vars are listed in Tables 1 and 2.Average seasonal performancerating for the 10 best African andFrench cultivars ranged from 2.9to 2.3 and 3.2 to 2.6, respectively.Cultivars in the ‘Antigua’ and‘Inca’ series were highly ratedamong the African type, andthose in the ‘Bonanza,’ ‘Bounty,’and ‘Hero’ series were highlyrated among the French type.

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2 Alabama Cooperative Extension System

Plug ProductionGrowers pay a premium price

for high-quality marigold seeds.Therefore, care and planning arenecessary to ensure that the maxi-mum number of transplantableseedlings will be produced froman ounce of seed. For the best re-sults in starting marigold seed,purchase F1 hybrid seeds fresheach season from a reputablesupplier. In planning the numberof seed to order for production,consider that there are 9,000 to13,000 seeds per ounce, depend-ing on the species and cultivar.

If seeds must be kept fromone season to the next, storethem in a dark, cool, dry environ-ment protected from insects androdents. As a general rule, storeseeds under conditions where the

sum of the Fahrenheit tempera-ture and percent relative humiditydoes not exceed 100. For exam-ple, where seeds are stored at45°F, the humidity should not ex-ceed 55 percent. Refrigeratorsdedicated to seed storage areoften used, with the seeds sealedin containers containing a desic-cant material.

The 406 or 512 plug flats aresmall enough for economic pro-duction but large enough to ac-commodate growth until trans-planting. However, larger plugsizes may be used to meet specialproduction goals. The most effec-tive way to sow marigold seeds isusing an automatic seeder. Usingan automatic seeder to sow mari-gold seeds can be problematicbecause the seeds are long and

Table 1. Best-Performing African Marigold Cultivars in the 1997 Trial1

Cultivar Flower Color Rating2

Antigua Primrose Yellow 2.9Antigua Goldsmith Gold 2.8Discovery Yellow Yellow 2.8Inca Yellow Yellow 2.7Inca Orange Orange 2.6Antigua Yellow Yellow 2.6Marvel Yellow Yellow 2.6Inca Mix Mix 2.5Marvel Deep Orange Orange 2.4Antigua Mixture Mix 2.31Trials held by Auburn University and Alabama Agricultural Experiment Station at theE.V. Smith Research Center.2Marigold cultivars were rated on a scale of 0 (dead) to 5 (superior plant in flower) forgarden performance.

Table 2. Best-Performing French Marigold Cultivars in the 1997 Trial1

Cultivar Flower Color Rating2

Bonanza Harmony Red 3.2Bonanza Flame Red 3.0Hero Orange Orange 2.9Bounty Yellow Yellow 2.8Hero Bee Red, yellow 2.8Bonanza Bee Red, yellow 2.8Hero Flame Red 2.8Bounty Goldsmith Yellow 2.8Bounty Spry Yellow, red 2.8Little Hero Flame Red 2.61Trials held by Auburn University and Alabama Agricultural Experiment Station at theE.V. Smith Research Center.2Marigold cultivars were rated on a scale of 0 (dead) to 5 (superior plant in flower) forgarden performance.

thin and the “fuzzy tail” (bristle-like projections at the basal endof the seed) interferes with themechanical seed-sowing process.Some brands of seeders comewith special attachments for han-dling marigold seed. Seed suppli-ers have also developed a seedthat has been “de-tailed.” Mari-gold seeds that are coated with a water-soluble, inert material tofacilitate sowing can also bepurchased.

Sow seeds in plug flats con-taining a moist, well-drained, ster-ile medium such as one of themany peat-lite mixes availablecommercially for plug culture.Germinating media pH should bein a range of 5.8 to 6.5, with anelectrical conductivity level of lessthan 0.75 mmhos/cm based onthe 2:1 extraction method. Beforesowing the seeds, thoroughlymoisten the medium with room-temperature water. Light is not re-quired for marigold seed germina-tion; therefore, sow seeds directlyon the medium surface, andcover the seeds with a thin layerof #2 coarse-grade vermiculite.Vermiculite helps maintain ade-quate moisture around the seed.

Seeds of the African andFrench types germinate in 3 to 5days at 75° to 80°F medium tem-perature. Seeds of the triploidtype may require several daysmore. Bottom heat greatly en-hances seed germination andearly growth, especially on cropsearly in the spring season. Keepthe germinating medium moist,but not saturated. Reduce themoisture level and reduce thenight temperature to 68° to 70°Fonce the radicle (root) emerges.Begin fertilizing seedlings once ortwice per week at 50 to 75 ppmnitrogen, using a 15-0-15 fertilizeror calcium nitrate and potassiumnitrate when cotyledons (seedleaves) unfold. Increase this rateto 100 to 150 ppm nitrogen whentrue leaves develop.

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Marigolds 3

Growing OnIf marigold plugs are pur-

chased from a propagator, unpackand examine the seedlings careful-ly. The plants should be an appro-priate size for transplanting. Over-grown seedlings are difficult togrow into high-quality plants, andseedlings that are too small are dif-ficult to transplant and slow to es-tablish. Remove several seedlingsfrom the sample flats, and examinethe root system. Marigold rootsshould be large, white, and fuzzy,covering about two-thirds of theouter surface of the medium. Lookfor signs of overwatering and rootdiseases indicated by brown orblack discoloration. Examine thefoliage for diseases, insects, ornutrient problems.

Be prepared to transplantplugs immediately. Generally,marigold seedlings are ready totransplant from plugs when threeto four mature leaves are present.It is important to transplant whenseedlings just begin to crowd.Marigold plugs are usually ship-ped at a size that is ready totransplant. Holding plugs in thegreenhouse for too long results instunting and premature flowering.Plant seedlings at about the samelevel at which they were growingin the plug trays, but no deeper.Dibble the transplant medium tothe depth of the root ball, andgently firm-in the seedlings. Waternewly planted seedlings thor-oughly immediately after trans-planting them.

Growing MediumA light, well-drained, peat-lite

medium with a 5.8 to 6.5 pH andan electrical conductivity less then1.0 mmhos/cm based on the 2:1extraction method is recommend-ed for growing on. The media pHshould be 5.8 or higher. A mediapH lower than 5.8 may cause ironand manganese toxicity.

Symptoms of toxicity appear asspeckling, necrotic margins,necrotic spots on the older leaves,and, in extreme cases, death ofthe growing tip. Toxicity symp-toms may also appear with theoverapplication of micronutrients.This may occur when the groweruses a water-soluble fertilizer con-taining micronutrients after add-ing a commercial micronutrientfertilizer during the mixing of themedium. Some marigold cultivarsare more sensitive to this problemthan others are.

TemperatureGrow marigolds at 60° to 65°F

night temperatures and 65° to72°F day temperatures for high-quality plants. Use 65°F nighttemperatures for a week to 10days after transplanting to estab-lish the root system, and thendrop to 60°F if desired.

FertilizationDo not fertilize marigolds for

7 to 10 days after transplanting oruntil the roots reach the sides andbottom of the container. There-after, fertilize on a constant liquidfertilization basis at 100 to 150ppm nitrogen, using a fertilizerabout equal in nitrogen andpotassium content. Many growersalternate between 20-10-20 and15-0-15 or calcium nitrate andpotassium nitrate applied once ortwice per week. If the media tem-perature is below 65°F, avoid fer-tilizers with nitrogen high in theammonium form (greater than 40percent), such as some 20-20-20formulations. Growers should testmedium pH and soluble salts

in-house on a weekly basis andsend samples for laboratory test-ing every 2 weeks. Recommen-ded foliar analysis ranges formarigolds are given in Table 3.Fertilizer rate can be reduced byone-half in the last week or twoto harden-off plants before theyare shipped to the retail market.

PhotoperiodMany marigold cultivars are

facultative short-day plants, mean-ing that plants flower more quick-ly under short day lengths butwill eventually flower regardlessof photoperiod. African cultivarsdisplay more of a photoperiodicresponse than French or triploidtypes do. The critical photoperiodfor Tagetes erecta is between 12.5and 13 hours, meaning that plantsflower more quickly at daylengths shorter than this. Cultivarsof the African type can achievefaster flowering if provided withartificial short days. Cover the cul-tivars with black cloth from 5:00P.M. to 8:00 A.M. daily. Start apply-ing black cloth in the first 2 to 3weeks after seed germination, be-ginning in late February. Usingthe black cloth will reduce theflowering time by up to 2 weeksand will produce more compactplants. Not all cultivars requireblack cloth, however. Recentbreeding work has focused ondeveloping African cultivars thatare day-length neutral; therefore,black cloth is not beneficial.Photoperiod control is rarelyneeded or practiced for theFrench and triploid marigoldsduring normal spring production.

Table 3. Marigold Normal Foliar Analysis Ranges

Element percentage Element ppm

N 3.32 to 3.62 Fe 92 to 115P 0.49 to 0.54 Mn 275 to 558K 2.79 to 2.88 Zn 76 to 97Ca 2.36 to 2.72 Cu 19 to 25Mg 1.33 to 1.44 B 34 to 40S 1.34 to 1.44 Mo 0.22 to 0.62

Source: Plant Analysis Handbook II, MicroMacro Publishing, 1996.

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J.R. Kessler, Jr., Extension Horticulturist, Assistant Professor, Horticulture, AuburnUniversity

For more information, call your county Extension office. Look in your telephone direc-tory under your county’s name to find the number.Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The AlabamaCooperative Extension System (Alabama A&M University and Auburn University) offers educational programs,materials, and equal opportunity employment to all people without regard to race, color, national origin, religion,sex, age, veteran status, or disability. UPS, 3M10, New July 1998, ANR-1125ANR-1125

LightMarigolds require as much

light as possible, especially withearly spring crops. When arrang-ing bedding plants in the produc-tion area, place marigold crops inthe brightest areas possible,preferably areas with glass orclear plastic glazing. Be sure thegreenhouse glazing is clean andfree of shading compound.

Growth RetardantGenerally, control seedling

growth and prevent stretching bymanaging the environment, nutri-tion, and water first, and thenapply chemical growth retardantsif necessary. Height control isusually not needed on the Frenchand triploid types. Marigolds re-spond to two applications of B-Nine at 2,500 ppm 1 weekapart or one application of Cyco-cel (750 to1,500 ppm), Bonzi (4to 10 ppm), or A-Rest (50 to 100ppm).

SchedulingCrop production times differ

not only for the three horticulturaltypes of marigolds but alsoamong cultivars within each type.Production time will generally de-crease as light intensity and tem-perature increase during thespring production season.Production time for Africanmarigold cultivars can also bemodified by natural photoperiod.Growers should therefore keepdetailed records of crop perfor-mance and timing to improvefuture scheduling efforts.

African TypesGenerally, the African culti-

vars require up to 2 weeks longerto flower than the French andtriploid types do. In the South-east, seedlings in 406 plug flatsgenerally require 5 weeks fromsowing to be ready to transplantand 5 to 6 weeks in jumbo mar-ket packs for a total productiontime of 10 to 11 weeks. The totalproduction time for a single plug-grown seedling in a 4-inch pot is11 to 12 weeks.

French TypesIn the Southeast, seedlings in

406 plug flats generally require 4to 5 weeks from sowing to beingready to transplant and 3 to 4weeks in 48- to 32-cell marketpacks for a total production timeof 7 to 9 weeks. The total produc-tion time for a single plug-grownseedling in a 4-inch pot is 10 to11 weeks. Ten-inch hanging bas-kets with four or five seedlingsper container require 10 to 13weeks total production time.

Triploid TypesIn the Southeast, seedlings in

406 plug flats generally require 5weeks from sowing to beingready to transplant and 2 to 3weeks in 48- to 32-celled marketpacks for a total production timeof 7 to 8 weeks. The total produc-tion time for a single plug-grownseedling in a 4-inch pot is 10 to11 weeks.

Common Problems

Insects and Related PestsSpider mites, aphids, thrips,

and leaf miners can be problemson marigolds. Slugs and snailscan be problems under dampconditions.

DiseasesA protective application of a

fungicide for Alternaria leaf spotis recommended, especially onthe African type. Damping-off(Pythium and Rhizoctonia) inseedlings and grey mold(Botrytis) on flowers can beproblems. Tomato spotted wiltvirus (TSWV) can be a majorproblem and is carried by thrips.Southern bacterial wilt (Pseudo-monus solanacearium) and bac-terial leaf spot (Pseudomonas sy-ringae var. tagetes) are seriousdiseases. Southern bacterial wiltcauses stunting, wilting, anddeath, while bacterial leaf spotcauses small black spots that turnnecrotic. There are no knowncontrols, so infected plantsshould be destroyed.

Specific control measures for insect and disease problemscan be found in the Alabama Pest Management Handbook—Volumes 1 and 2 (ANR-500A and500B). For information about ob-taining this publication, contactyour county Extension agent.ARCHIVE