Annuals By Rick Schoellhorn

Winter Trials of Vegetative Annuals in Florida

While northern growers begin specialty annual production in spring and continue production through summer, the Deep South industry runs on an almost inverse schedule for these generally cool season crops. Production in Florida begins as temperatures drop in fall and continues through the beginning of the warm nights in early summer. The Mediterranean-type specialty annuals such as Sutera (Bacopa), Brachycome, Osteospermum, Argyranthemum, Nemesia fruticans and Diascia all prefer cool nights and low humidity. Fall through spring in the Deep South provides these conditions, while summer heat and humidity generally signal the end of these plants due to disease pressure and a lack of heat tolerance.

Southern landscapers usually stay away from specialty annuals. Their susceptibility to diseases in the summer and their freeze sensitivity usually limit their use to the short weeks between summer heat and first winter freeze, or the even shorter time between last freeze and the high summer temperatures. Most people, as a result, are limited to using the basics for winter and fall color. Pansies, violas and ornamental kale traditionally provide the backbone of the winter annual industry in the Deep South.

The winter trials I present here were part of an evaluation of specialty annuals to broaden the winter palate of color available to homeowners and landscapers in Florida and other regions of the Deep South. The goal of the trials was not only to find out what does well in southern winters, but also what plants can be established in fall for longer – and more impressive – spring flowering.

There are many trial gardens in the state of Florida; some are private, others are public gardens where the emphasis is on display, while evaluations go on behind the scenes. What is the purpose of these trial gardens? How is their information made available to industry and the consumer? These questions are part of a seminar entitled “Southeastern Trial Gardens” at the Southeast Greenhouse Conference and Tradeshow in Greenville, S.C. in June 2001.

For the University of Florida, there are currently two main gardens: 1) The Milton Gardens, in northwest Florida, for vegetative plug evaluations, and 2) The trial gardens at the Gulf Coast Research Center, Bradenton, Fla., where the statewide seed industry evaluations are held.

Trialing methods

Trials are all in full sun with at least six full hours of sun per day. Plants are spaced on approximately 10-inch centers, slow release fertilizer is incorporated at planting and a 2-inch layer of cedar mulch is placed over the soil surface. Every two years the beds are amended with mushroom compost at a rate of about one cubic yard of compost for every 200 square feet. Plants are evaluated for quality at planting and every four weeks thereafter throughout the season.

Trials and evaluations are done both in plastic beds and landscape plantings. While both methods have some merit, the plastic beds (similar to those used in commercial vegetable row crop production) generate a more positive rating for marginal plants, especially the specialty annuals. Plastic bed trials are actually a bit like container trials in that the amount of splashback from rain, and therefore disease pressure, is reduced. The landscape trials, however, inevitably provide a much more realistic evaluation.

Table 1 displays the rating system used in the Milton Gardens.

Winter trials

In the 2000-2001 winter trials, plants were obtained from EuroAmerican Propagators and represent both the Proven Winners and EuroSelect collections. Results are shown in Table 2.

Field trials. All plants were planted on October 10—15, 2000, and Osmocote 14-14-14 with minors was incorporated at medium label rates. The winter of 2000 has proven so far to be the coldest winter in over six years for this region of the state. Beginning with first frost on November 12 and experiencing over three weeks with night temperatures below 30° F in December, the trials faced a much more demanding test than we expected.

Greenhouse trials. Greenhouse trials were completed in 10-inch hanging baskets, unless otherwise noted, using Fafard #2 mix, constant feed with Peters 15-5-15, natural photoperiod and temperatures of 58° F night and 75° F day. The average light level was 550 µmol·m2·s-1. All ratings were done at 12 weeks from planting, so baskets evaluated were large and past market in terms of shipping. However, performance ratings are averages of the entire production cycle.

General results

In general, the year 2000 proved too much for many of the plants in the trials. Six nights below 20° F and 12 nights below 30° F took a high toll among the trial materials. However, there are two categories (shown in Fig. 1) worthy of further consideration: those plants that came through the winter relatively undamaged by the freezes (winter hardy) and those plants that may not add anything to the landscape, but are alive and well (semi hardy), will be established for extended spring flowering. If the 2000 winter is colder than “normal,” performance on both sets of plants could be expected to improve during milder winters.

While these “hardiness” ratings will be fairly specific for areas along the latitude of northern Florida, they are also true for growers a little farther north in cool greenhouse production or in getting a jump on the spring season.

One thing we can say for harsher winters is that they bring the customers out in spring to replace what was lost over the winter. With last year’s drought, most growers are looking for a strong spring to get things back on track for 2001. These are some crops with excellent potential. Other strong crops for spring, based on previous years of trialing in north Florida’s Milton gardens, appear in Table 3.

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Rick Schoellhorn

Rick Schoellhorn is assistant professor of environmental horticulture at the University of Florida, Milton, Fla.

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