ALABAMA A&M AND AUBURN UNIVERSITIES Greenhouse Production

ANR-1125 of Marigolds

arigolds have long major horticultural types are the Triploid Type African type, the French type, and been popular with Triploid cultivars are breeding the triploid type. crosses between Tagetes erecta American gardeners Breeders have worked exten- and Tagetes patula. One advan- as one of the pre- sively to create cultivars in a wide tage of these cultivars is that they Mmiere summer annuals. They per- range of colors, plant sizes, and provide the longest overall dis- form well in dry, hot, sunny loca- flower forms. Marigold flowers play of color in the landscape, are available in single, semidou- often lasting through the hot sum- tions and produce dark-green, ble, or double petal arrangements mer weather into August and fine-textured foliage and bright- with white, yellow to orange, September. However, seed germi- colored flowers throughout the gold, or red flowers. Red and nation during production may be crimson flower colors are found summer and into the fall. There considerably slower than for the in the triploid and French types African and French types. These may be more sizes, flower types, but not in the African type. plants are sterile, so they will not and growth habits of marigolds Flower sizes range from 1 inch in produce viable seed. than of any other bedding plant. the French type to 5 inches in the Marigolds range in size from 6 African type. Best-Performing inches to over 3 feet tall. Dwarf Cultivars cultivars are appropriate to use in African Type containers, as bedding plants, or Cultivars of Tagetes erecta, The Alabama Agricultural as flower bed borders, while taller sometimes referred to as Ameri- Experiment Station has estab- cultivars can be used as bed can marigolds, are larger plants lished a trial garden at the E.V. fillers, at the rear of the border, or than the French type, often with Smith Research Center near as cut flowers. In the past, mari- fewer, larger double flowers. In Shorter, Alabama, to evaluate an- golds had a strong fragrance that the double-flowered cultivars, nual garden plants. Fourteen some people found objectionable. there are crested doubles, whose African cultivars and 25 French Newer cultivars are somewhat flowers are mounded and full, cultivars were visually rated bi- less pungent, but they still have and anemone doubles whose monthly on a scale of 0 (dead) to the characteristic marigold smell. flowers are flat and wide with a 5 (superior plants in flower) for recessed center. garden performance during the Cultivars summer of 1997. The 10 best-per- French Type forming African and French culti- Two different species of vars are listed in Tables 1 and 2. marigold are commonly grown: Cultivars of Tagetes patula are Average seasonal performance African marigolds (Tagetes erecta) usually smaller than African type rating for the 10 best African and and French marigolds (Tagetes plants. Most are 6 to 8 inches, but French cultivars ranged from 2.9 patula). Interestingly, ARCHIVEneither some cultivars reach 12 inches in to 2.3 and 3.2 to 2.6, respectively. African nor French marigolds height. Though double flower Cultivars in the ‘Antigua’ and come from Africa or France— petal arrangements are available, ‘Inca’ series were highly rated both species are native to New single and semidouble are more among the African type, and Mexico and Arizona and south- common. The single-flowering those in the ‘Bonanza,’ ‘Bounty,’ ward to Argentina. Crosses be- cultivars stand up to rain and hu- and ‘Hero’ series were highly tween African and French mari- midity better in the South than rated among the French type. golds have resulted in triploid double-flowered cultivars do. cultivars; therefore, the three

Visit our Web site at: www.acesag.auburn.edu Table 1. Best-Performing African Marigold Cultivars in the 1997 Trial1 thin and the “fuzzy tail” (bristle- Cultivar Flower Color Rating2 like projections at the basal end Antigua Primrose Yellow 2.9 of the seed) interferes with the Antigua Goldsmith Gold 2.8 mechanical seed-sowing process. Discovery Yellow Yellow 2.8 Some brands of seeders come Inca Yellow Yellow 2.7 with special attachments for han- Inca Orange Orange 2.6 dling marigold seed. Seed suppli- Antigua Yellow Yellow 2.6 ers have also developed a seed Marvel Yellow Yellow 2.6 that has been “de-tailed.” Mari- Inca Mix Mix 2.5 gold seeds that are coated with Marvel Deep Orange Orange 2.4 a water-soluble, inert material to Antigua Mixture Mix 2.3 facilitate sowing can also be 1Trials held by Auburn University and Alabama Agricultural Experiment Station at the purchased. E.V. Smith Research Center. 2Marigold cultivars were rated on a scale of 0 (dead) to 5 (superior plant in flower) for Sow seeds in plug flats con- garden performance. taining a moist, well-drained, ster- ile medium such as one of the Table 2. Best-Performing French Marigold Cultivars in the 1997 Trial1 many peat-lite mixes available Cultivar Flower Color Rating2 commercially for plug culture. Bonanza Harmony Red 3.2 Germinating media pH should be Bonanza Flame Red 3.0 in a range of 5.8 to 6.5, with an Hero Orange Orange 2.9 electrical conductivity level of less Bounty Yellow Yellow 2.8 than 0.75 mmhos/cm based on Hero Bee Red, yellow 2.8 the 2:1 extraction method. Before Bonanza Bee Red, yellow 2.8 sowing the seeds, thoroughly Hero Flame Red 2.8 moisten the medium with room- Bounty Goldsmith Yellow 2.8 temperature water. Light is not re- Bounty Spry Yellow, red 2.8 quired for marigold seed germina- Little Hero Flame Red 2.6 tion; therefore, sow seeds directly 1Trials held by Auburn University and Alabama Agricultural Experiment Station at the E.V. Smith Research Center. on the medium surface, and 2Marigold cultivars were rated on a scale of 0 (dead) to 5 (superior plant in flower) for cover the seeds with a thin layer garden performance. of #2 coarse-grade vermiculite. Vermiculite helps maintain ade- Plug Production sum of the Fahrenheit tempera- quate moisture around the seed. ture and percent relative humidity Seeds of the African and Growers pay a premium price does not exceed 100. For exam- French types germinate in 3 to 5 for high-quality marigold seeds. ple, where seeds are stored at days at 75° to 80°F medium tem- Therefore, care and planning are 45°F, the humidity should not ex- perature. Seeds of the triploid necessary to ensure that the maxi- ceed 55 percent. Refrigerators type may require several days mum number of transplantable dedicated to seed storage are more. Bottom heat greatly en- seedlings will be produced from often used, with the seeds sealed hances seed germination and an ounce of seed. For the best re- in containers containing a desic- early growth, especially on crops sults in starting marigold seed, cant material. early in the spring season. Keep purchase F1 hybrid seeds fresh the germinating medium moist, each season from a reputable The 406 or 512 plug flats are small enough for economic pro- but not saturated. Reduce the supplier. In planning the number moisture level and reduce the of seed to order for production, duction but large enough to ac- commodate growth until trans- night temperature to 68° to 70°F consider that there are 9,000 to once the radicle (root) emerges. 13,000 seeds per ounce, depend- planting. However, larger plug ARCHIVEsizes may be used to meet special Begin fertilizing seedlings once or ing on the species and cultivar. production goals. The most effec- twice per week at 50 to 75 ppm If seeds must be kept from tive way to sow marigold seeds is nitrogen, using a 15-0-15 fertilizer one season to the next, store using an automatic seeder. Using or calcium nitrate and potassium them in a dark, cool, dry environ- an automatic seeder to sow mari- nitrate when cotyledons (seed ment protected from insects and gold seeds can be problematic leaves) unfold. Increase this rate rodents. As a general rule, store because the seeds are long and to 100 to 150 ppm nitrogen when seeds under conditions where the true leaves develop.

2 Alabama Cooperative Extension System Growing On Symptoms of toxicity appear as in-house on a weekly basis and speckling, necrotic margins, send samples for laboratory test- If marigold plugs are pur- necrotic spots on the older leaves, ing every 2 weeks. Recommen- chased from a propagator, unpack and, in extreme cases, death of ded foliar analysis ranges for and examine the seedlings careful- the growing tip. Toxicity symp- marigolds are given in Table 3. ly. The plants should be an appro- toms may also appear with the Fertilizer rate can be reduced by priate size for transplanting. Over- overapplication of micronutrients. one-half in the last week or two grown seedlings are difficult to This may occur when the grower to harden-off plants before they grow into high-quality plants, and uses a water-soluble fertilizer con- are shipped to the retail market. seedlings that are too small are dif- taining micronutrients after add- ficult to transplant and slow to es- ing a commercial micronutrient tablish. Remove several seedlings Photoperiod fertilizer during the mixing of the from the sample flats, and examine Many marigold cultivars are medium. Some marigold cultivars the root system. Marigold roots facultative short-day plants, mean- are more sensitive to this problem should be large, white, and fuzzy, ing that plants flower more quick- than others are. covering about two-thirds of the ly under short day lengths but outer surface of the medium. Look will eventually flower regardless for signs of overwatering and root Temperature of photoperiod. African cultivars diseases indicated by brown or Grow marigolds at 60° to 65°F display more of a photoperiodic black discoloration. Examine the night temperatures and 65° to response than French or triploid foliage for diseases, insects, or 72°F day temperatures for high- types do. The critical photoperiod nutrient problems. quality plants. Use 65°F night for Tagetes erecta is between 12.5 Be prepared to transplant temperatures for a week to 10 and 13 hours, meaning that plants plugs immediately. Generally, days after transplanting to estab- flower more quickly at day marigold seedlings are ready to lish the root system, and then lengths shorter than this. Cultivars transplant from plugs when three drop to 60°F if desired. of the African type can achieve to four mature leaves are present. faster flowering if provided with It is important to transplant when Fertilization artificial short days. Cover the cul- seedlings just begin to crowd. Do not fertilize marigolds for tivars with black cloth from 5:00 P.M. to 8:00 A.M. daily. Start apply- Marigold plugs are usually ship- 7 to 10 days after transplanting or ing black cloth in the first 2 to 3 ped at a size that is ready to until the roots reach the sides and weeks after seed germination, be- transplant. Holding plugs in the bottom of the container. There- ginning in late February. Using greenhouse for too long results in after, fertilize on a constant liquid the black cloth will reduce the stunting and premature flowering. fertilization basis at 100 to 150 flowering time by up to 2 weeks Plant seedlings at about the same ppm nitrogen, using a fertilizer and will produce more compact level at which they were growing about equal in nitrogen and plants. Not all cultivars require in the plug trays, but no deeper. potassium content. Many growers black cloth, however. Recent Dibble the transplant medium to alternate between 20-10-20 and breeding work has focused on the depth of the root ball, and 15-0-15 or calcium nitrate and developing African cultivars that gently firm-in the seedlings. Water potassium nitrate applied once or are day-length neutral; therefore, newly planted seedlings thor- twice per week. If the media tem- black cloth is not beneficial. oughly immediately after trans- perature is below 65°F, avoid fer- Photoperiod control is rarely planting them. tilizers with nitrogen high in the needed or practiced for the ammonium form (greater than 40 French and triploid marigolds Growing Medium percent), such as some 20-20-20 during normal spring production. A light, well-drained, peat-lite formulations. Growers should test medium with a 5.8 to 6.5 pH and medium pH and soluble salts an electrical conductivityARCHIVE less then 1.0 mmhos/cm based on the 2:1 Table 3. Marigold Normal Foliar Analysis Ranges extraction method is recommend- Element percentage Element ppm ed for growing on. The media pH N 3.32 to 3.62 Fe 92 to 115 should be 5.8 or higher. A media P 0.49 to 0.54 Mn 275 to 558 pH lower than 5.8 may cause iron K 2.79 to 2.88 Zn 76 to 97 and manganese toxicity. Ca 2.36 to 2.72 Cu 19 to 25 Mg 1.33 to 1.44 B 34 to 40 S 1.34 to 1.44 Mo 0.22 to 0.62 Source: Plant Analysis Handbook II, MicroMacro Publishing, 1996.

Marigolds 3 Light African Types Common Problems Marigolds require as much Generally, the African culti- light as possible, especially with vars require up to 2 weeks longer Insects and Related Pests early spring crops. When arrang- to flower than the French and Spider mites, aphids, thrips, ing bedding plants in the produc- triploid types do. In the South- and leaf miners can be problems tion area, place marigold crops in east, seedlings in 406 plug flats on marigolds. Slugs and snails the brightest areas possible, generally require 5 weeks from can be problems under damp preferably areas with glass or sowing to be ready to transplant conditions. clear plastic glazing. Be sure the and 5 to 6 weeks in jumbo mar- greenhouse glazing is clean and ket packs for a total production free of shading compound. time of 10 to 11 weeks. The total Diseases production time for a single plug- A protective application of a Growth Retardant grown seedling in a 4-inch pot is fungicide for Alternaria leaf spot 11 to 12 weeks. is recommended, especially on Generally, control seedling the African type. Damping-off growth and prevent stretching by French Types (Pythium and Rhizoctonia) in managing the environment, nutri- seedlings and grey mold tion, and water first, and then In the Southeast, seedlings in (Botrytis) on flowers can be apply chemical growth retardants 406 plug flats generally require 4 problems. Tomato spotted wilt if necessary. Height control is to 5 weeks from sowing to being virus (TSWV) can be a major usually not needed on the French ready to transplant and 3 to 4 problem and is carried by thrips. and triploid types. Marigolds re- weeks in 48- to 32-cell market Southern bacterial wilt (Pseudo- spond to two applications of packs for a total production time monus solanacearium) and bac- B-Nine at 2,500 ppm 1 week of 7 to 9 weeks. The total produc- terial leaf spot (Pseudomonas sy- apart or one application of Cyco- tion time for a single plug-grown ringae var. tagetes) are serious cel (750 to1,500 ppm), Bonzi (4 seedling in a 4-inch pot is 10 to diseases. Southern bacterial wilt to 10 ppm), or A-Rest (50 to 100 11 weeks. Ten-inch hanging bas- causes stunting, wilting, and ppm). kets with four or five seedlings death, while bacterial leaf spot per container require 10 to 13 causes small black spots that turn Scheduling weeks total production time. necrotic. There are no known Crop production times differ controls, so infected plants not only for the three horticultural Triploid Types should be destroyed. types of marigolds but also In the Southeast, seedlings in Specific control measures among cultivars within each type. 406 plug flats generally require 5 for insect and disease problems Production time will generally de- weeks from sowing to being can be found in the Alabama crease as light intensity and tem- ready to transplant and 2 to 3 Pest Management Handbook— perature increase during the weeks in 48- to 32-celled market Volumes 1 and 2 (ANR-500A and spring production season. packs for a total production time 500B). For information about ob- Production time for African of 7 to 8 weeks. The total produc- taining this publication, contact marigold cultivars can also be tion time for a single plug-grown your county Extension agent. modified by natural photoperiod. seedling in a 4-inch pot is 10 to Growers should therefore keep 11 weeks. detailed records of crop perfor- mance and timing to improve future scheduling efforts.ARCHIVE J.R. Kessler, Jr., Extension Horticulturist, Assistant Professor, Horticulture, Auburn University 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 June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative 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, ANR-1125 sex, age, veteran status, or disability. UPS, 3M10, New July 1998, ANR-1125