Best-of-Class Marigolds By Rick Kelly, Rick Schoellhorn, Zhanao Deng and Brent Harbaugh

The University of Florida runs its trials a bit differentlythan most universities. Instead of numerous cultivars, it focuses on only oneand its different varieties. Thus last year, marigolds were the university’strial target.

Evaluation Method. Seed-propagated annual bedding plants areevaluated by the University of Florida at the Gulf Coast Research and EducationCenter in Bradenton, Fla., (AHS Heat Zone 10; USDA Cold Hardiness Zone 9b) inthe spring, fall and winter using a new “best-of-class” format. Alltrials are fully replicated, meaning 5-6 plants of each cultivar are planted in3-4 plots that are randomly placed in the field. We believe multiple plantingsof each cultivar provide a more accurate picture of field performance comparedto single plot plantings. In addition, two fields are planted for each test.One field is scouted for pests and sprayed when necessary (resembling acommercial planting), and cultivar performance is then evaluated. The otherfield receives no pesticides (reflecting a homeowner’s planting), and pestsymptoms are evaluated.

Data collection.Objective data — plant height, width and flower size — and subjective data –plant, foliage and flower characteristics — are collected several times duringthe season. The data is presented in tables that allow performance evaluationover the course of the season, or selection of specific data, such as flowersize or plant height. Data from both fields is combined to yield an overallperformance rating, the highest rated plant being selected”best-of-class.”

The best-of-class system is a method we developed to reducerepetitive testing of old cultivars. Selecting best-of-class cultivars providesus with one representative cultivar for each class as a standard for comparisonwith the new cultivars released every year. Once a cultivar is evaluated, we donot trial it again. Instead, we only trial newly released or improved cultivarsto determine if they outperform the best-of-class. If they do, the previous isreplaced.

Trials at the Gulf Coast Research & Education Center(GCREC) are designed to gain maximum exposure to a wide audience. Because thisresearch is replicated, it may be published in scientific journals in additionto trade and popular gardening magazines. These trials have also been featuredon NPR radio, Associated Press articles and regional television, as well aslocal newspapers. The GCREC Web site ( providespictures, detailed research reports and many useful links. For thebest-of-class from the 2001 trial of pansies, see the January 2002 issue ofGPN.

Marigold Trials

Materials and methods.Between fall 1999 and spring 2002, 44 cultivars that included African, French,triploid and signet marigolds were evaluated. Cultural methods have evolved overthe seasons to produce a sturdy, compact plug by limiting available phosphorousand ammonium. Currently, we use a commercial mix supplied for seed sowing andplug production that does not contain phosphate (Farfard Custom ProfessionalMix with a pH of 6.0, formula: 60 percent peat, 40 percent vermiculite; 3 lb.dolomite; 1 lb. micro max; 1 lb gypsum), and a 15-4.1-6.5 NPK water-solublefertilizer solution containing nitrogen at 250 mgáL-1(15-5-15 Ca-MgExcel; The Scotts Co., Maryville, Ohio).

Seeds were allowed to germinate between 72-75¡ F in agrowth room with a photosynthetic photon flux of 30µmolám-2ás-1 under cool-white fluorescent lamps from 8-12hours. Immediately after germination, seedlings were transplanted into a 128-celltray and placed into a screen-sided, fiberglass-covered greenhouse. Flats weretreated with a fungicidal drench of Banrot WP the day before planting in thefield.

Plugs were transplanted into raised ground beds with sixplants per plot spaced 12 inches apart in a staggered layout. Beds were 32inches wide x 8 inches high. We applied 15-3.9-10.0 NPK Osmocote Plus (15-9-12,5-6 mo. slow release type) fertilizer by hand to each plant on the soil surfaceapproximately an inch from the plant stem under the plastic mulch at 262 lb.nitrogen per row acre of nitrogen. Beds were fumigated around 14 days beforeplanting with a mixture of 66 percent methyl bromide and 33 percentchloropicrin at 350 lb. per acre and covered with white-on-black polyethylenefilm. Subsurface irrigation water was supplied from lateral ditches spaced 42feet apart.

We used a rating scale ranging from 7 (excellent) to 1(poor), with 7 representing all plants in a plot having full and uniformfoliage/flowers, plants free of pest symptoms and abnormalities or weaknessessuch as lodging; 4 representing average foliage/flower density, minimallodging, and/or some pest damage, but foliage/flowers still acceptable; and 1representing sparse foliage/flowers, stem lodging, and/or unacceptable pestdamage, making plants undesirable. We evaluated plants three times each seasonin order to provide performance information on flowering and vegetativecharacteristics over time.

Best of Class Selections. While our irrigation/soil-type/fertilization practices may notrepresent cultural practices in other landscape situations, our choice of thesegrowing conditions was to provide uniform and satisfactory nutrients andmoisture to allow for outstanding growth and flowering of marigolds. Soilamendments and irrigation are typically used in bedding plant trials, andindeed, most gardeners and landscapers modify their soil and provideirrigation/fertilizer to maximize growth and flowering. Thus, performanceevaluations for bedding plants are more likely influenced by climatic conditionsthan by culture.

The information in this report is a summary of experimentalresults and does not provide recommendations for crop production. Where tradenames are used, no discrimination is intended or endorsement implied.

In general, cultivars with ratings greater than 5 wereconsidered outstanding, 4-4.9 were considered good performers and less than 3.9as fair to poor. The performance of a cultivar in a class may not be acceptableand may still be the best for that class. Most of these cultivars were good tooutstanding performers. Breeding companies will have quite a challenge torelease new cultivars with better performance.

Note: The information in this report is a summary ofexperimental results and does not provide recommendations for crop production.Where trade names are used, no discrimination is intended or endorsementimplied. You can find more about the statewide trials at

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Rick Kelly, Rick Schoellhorn, Zhanao Deng and Brent Harbaugh

Rick Kelly is the variety trials coordinator, Rick Schoellhorn and Zhanao Deng are assistant professors of floriculture and Brent Harbaugh is professor of floriculture at the University of Florida. They can be reached by phone at (941) 751-7636 or E-mail at [email protected]

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