Best-of-Class Marigolds

May 8, 2003 - 09:27

University of Florida trialing data rates all currently available marigolds.

The University of Florida runs its trials a bit differently
than most universities. Instead of numerous cultivars, it focuses on only one
and its different varieties. Thus last year, marigolds were the university's
trial target.

Evaluation Method. Seed-propagated annual bedding plants are
evaluated by the University of Florida at the Gulf Coast Research and Education
Center in Bradenton, Fla., (AHS Heat Zone 10; USDA Cold Hardiness Zone 9b) in
the spring, fall and winter using a new "best-of-class" format. All
trials are fully replicated, meaning 5-6 plants of each cultivar are planted in
3-4 plots that are randomly placed in the field. We believe multiple plantings
of each cultivar provide a more accurate picture of field performance compared
to single plot plantings. In addition, two fields are planted for each test.
One field is scouted for pests and sprayed when necessary (resembling a
commercial planting), and cultivar performance is then evaluated. The other
field receives no pesticides (reflecting a homeowner's planting), and pest
symptoms are evaluated.

Data collection.
Objective data -- plant height, width and flower size -- and subjective data --
plant, foliage and flower characteristics -- are collected several times during
the season. The data is presented in tables that allow performance evaluation
over the course of the season, or selection of specific data, such as flower
size or plant height. Data from both fields is combined to yield an overall
performance rating, the highest rated plant being selected

The best-of-class system is a method we developed to reduce
repetitive testing of old cultivars. Selecting best-of-class cultivars provides
us with one representative cultivar for each class as a standard for comparison
with the new cultivars released every year. Once a cultivar is evaluated, we do
not trial it again. Instead, we only trial newly released or improved cultivars
to determine if they outperform the best-of-class. If they do, the previous is

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

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 over
the seasons to produce a sturdy, compact plug by limiting available phosphorous
and ammonium. Currently, we use a commercial mix supplied for seed sowing and
plug production that does not contain phosphate (Farfard Custom Professional
Mix 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-soluble
fertilizer solution containing nitrogen at 250 mg·L-1(15-5-15 Ca-Mg
Excel; The Scotts Co., Maryville, Ohio).

Seeds were allowed to germinate between 72-75° F in a
growth room with a photosynthetic photon flux of 30
µmol·m-2·s-1 under cool-white fluorescent lamps from 8-12
hours. Immediately after germination, seedlings were transplanted into a 128-cell
tray and placed into a screen-sided, fiberglass-covered greenhouse. Flats were
treated with a fungicidal drench of Banrot WP the day before planting in the

Plugs were transplanted into raised ground beds with six
plants per plot spaced 12 inches apart in a staggered layout. Beds were 32
inches 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 surface
approximately 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 before
planting with a mixture of 66 percent methyl bromide and 33 percent
chloropicrin at 350 lb. per acre and covered with white-on-black polyethylene
film. Subsurface irrigation water was supplied from lateral ditches spaced 42
feet apart.

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

Best of Class Selections normal'>. While our irrigation/soil-type/fertilization practices may not
represent cultural practices in other landscape situations, our choice of these
growing conditions was to provide uniform and satisfactory nutrients and
moisture to allow for outstanding growth and flowering of marigolds. Soil
amendments and irrigation are typically used in bedding plant trials, and
indeed, most gardeners and landscapers modify their soil and provide
irrigation/fertilizer to maximize growth and flowering. Thus, performance
evaluations for bedding plants are more likely influenced by climatic conditions
than by culture.

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

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

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

About The Author

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

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