University of Florida Field Trials By Rick Schoellhorn

Let’s face it, climates are different in Florida, Michiganand Colorado, which can generate some very different results from trialgardens. What succeeds in high heat and humidity may not succeed under coolnights with low relative humidity, and vice versa. So patronize your localtrials gardens and make a point of learning their results; it’s the best anygrower can do if they are concerned about local performance.

Compiled ratings from trial gardens around the United Statescan, however, be a great “Big Picture” source. But remember that anorthern garden’s recommendations may only be good for spring or even winterperformance in the South. On the other hand, a summer rating in Florida willindicate to northern growers that a plant has an extended season where summersare hot.

The spring field trials at the University of Florida thisyear contained 180 cultivars of vegetative annuals, both those more common tosouthern production and also several focus areas. Focus crops for these trialswere: seed-produced spreading petunias, vinca major (periwinkle),”perennial” verbena, vegetative torenia, helichrysum, cuphea species,porter weed, calibrachoa, plectranthus, vegetative catharanthus (vinca) andvegetative coleus. (Information about helichrysum and vinca major can be foundin the August issue of GPN.) The trials extended from April 15 when plantingsbegan to August 7 when crops that were past landscape value were removed. Westill have about 70 cultivars in the gardens as of September 10 that are goingstrong, but more about that later.

The goal of these trials is to promote plants that aretolerant of extreme high heat and humidity, conditions common across thesoutheast sunbelt from Florida to West Texas. Obviously, the season here beginsvery early in the year and, for some plants, ends a lot earlier as well. Theresults of these trials can be used to help growers refine their late-seasonselections where heat and humidity have the biggest impact on crop quality.

Trial Essentials

How we set up our trials. Three 120- x 8-foot trial beds were installed in a full sun andturfgrass area with established bermuda and bahia grass. The area had not beenworked previously and was amended with mushroom compost at 1 yd3/100 ft2. SoilpH ranged from 5.2-6.6. Amending the soil brought the pH up to 6.0-6.8.

Twelve plants of each cultivar were grown from liner to4-inch pot in our greenhouses. These plants were planted on 1-foot spacings,and received nine grams of Osmocote slow-release 18-6-12 fertilizer (3-monthformulation) incorporated into each planting hole. Beds were mulched betweenplants with Cypress mulch at an average depth of 4 1/2 inches. Beds wereirrigated using commercial drip tape and watered twice each week. Throughoutthe season, no other fertilizer, fungicide or pesticide was applied.

What we measure. Wekeep track of first flower date, peak flower date, the time it takes to form acanopy over the test plot, vigor and visual quality (0 = dead, 1 = poor, 2 =fair, 3 = OK, 4 = good color and display, 5 = excellent, of superior quality).It can be roughly stated that any plant with a 2 or lower rating is notconsidered worth the effort needed to plant it. But remember, these are fieldtrials, not greenhouse or container trials; performance under the two can bevery different. The biggest factor affecting outdoor performance in Florida israin. Our rains are usually in the afternoon and completely wet the foliage asthe sun is setting, a recipe for disease.

How we report our findings. Our trials are online at www.hort.ifas.ufl.edu; just click on the”new” button and select spring trials. The focus crops are allphotographed every other week, allowing you to virtually watch the plants growthroughout the trial.

Trial summary. Thiswas a dry spring and early summer in Gainesville, which really extended theseason for a lot of the cool, dry preference crops. When our rains began inJune, the differences became very obvious in terms of what can take heat andhumidity and what can’t. Even so, there were a lot of surprises with crops thatheld on and looked good long past the onset of rainy weather. Even now, almosta month after the trials are completed, Helichrysum petiolare still lookspretty good, which no one expected.

Seed-produced trailing petunias

This type of petunia grows more popular each year, and everyone of the trialed cultivars had a period of weeks where it rated a perfect 5.So there were no losers in the group. All began to deteriorate around week 26when the rains kicked in.

Wave Purple (PanAmerican Seed) received the highest average rating for the season (trial endedweek 26). The Wave series is definitely the most heat-tolerant andlong-flowering. Good colors and a low spreading habit. All cultivars clungtightly to the ground and persisted longest into the heat.

Ramblin’ Lilac Glow(Goldsmith Seed) was the earliest-flowering in the landscape. This variety hada more mounding habit, with good-sized flowers and a quick growth to cover thetrial plot. This growth habit caused it some problems later in the season withlodging, but all in all it was a good early-season performer.

Plectranthus

Yeah, yeah I know I talk too much about these plants, but wehad 22 releases in the trial this year, and there were some interestingresults. Really; there were.

Plectranthus madagascariensis, also called P. coleoides ‘variegatus’ and P. iboza ‘coleoides’),whatever; they are all the same plant (EuroAmerican, HMA and my mother’sgarden) and all were basically the same in their performance, which was solidwith great uniformity and foliage color through the season. These plants arestill holding strong.

Plectranthus ‘Nicoletta’ (Ball FloraPlant) has silvery foliage similar to P. argentatus but amuch better growth habit, disease-free foliage and a lot of vigor. We reallynever saw much flowering on this species, but it has been a greathumidity-tolerant, gray foliage accent and is still growing strong.

Plectranthus ecklonii(San Felasco Nursery, Silverhill Seed) are really beginning to bloom as we moveinto September. Plants are from 3-4 feet tall and masses of lavender and pinkflowers add another foot to plant height. A Silverwood Seed selection fromSouth Africa, ‘Medleywood’ is only budding up now but should be blooming inanother week.

In general, the species we grew from South Africa have notbeen commercially acceptable for foliage or flowering, but there is some nicematerial there.

Novelty crops

Novelty crops, specialty annuals, component plants, callthem what you will, but this is some of the most interesting plant materialaround. It is important to keep track of the commodity crops, but for growersand retailers, this is the material to fill in profit gaps, personalize yourproduct mix and create a strong niche. The plants in this category offer a lotof variety, as well as heat and drought tolerance.

Allamanda schottii — Dwarf Allamanda (Hatchett Creek Farms). Allamanda is known in theSouth for its drought tolerance and non-stop summer flowering, but most formsare gangly and semi-vining. Still blooming in September, these plants havenever gotten more than three feet tall and are covered with bright yellow4-inch flowers. Great form, but slow starting when conditions are cool.

Bulbine caulescens — Yellow Bulbine (Yucca Do Nursery). A little-known relative ofaloe, this was a really strong performer, with flowers from planting datethrough; well; it was still going in September. Needs a hot, sunny, drylocation. This one is larger than the orange, which is also hard to find but verymuch worth the effort.

Cleome species — Linda Armstrong (EuroAmerican Propagators). Fantastic color. Thisplant was in bloom from liner through late July with pale ç lilac-pinkflowers atop purpleish foliage. Much smaller in stature than seed-producedcleome.

Hemigraphis coloratus (Boynton Botanicals). A relative ofthe old houseplant called “Waffle Plant,” this species is a foliagecolor form with purple, burgundy foliage, frosted with silver. It has held upand grown well in full afternoon sun for the entire season. Much the sameeffect and color range as ajuga foliage, but much better in the heat and sun.

Nolana species — Blue Eyes (Bodger Botanicals). Not a particularly easy plant to make look good ina container, but in the field this was a beautiful, petunia-like flower withstriking blue blooms and a very vigorous growth habit. Lasted as well or betterthan petunias (finished in week 26), and offered something different in flowercolor and foliage texture. Very strong.

Otacanthus caerulus — Brazilian Snapdragon (Bodger Botanicals). Killer, intense sky blueflowers on an irregularly shaped plant, this was strong and colorful in theearly season; it shuts down in the heat of the Southern summer, but is alreadypicking up again for a fall flush. Tender perennial in the South, with goodperformance. Hey, Jim Barrett likes this plant, and he thinks all componentplants are weeds!

Salvia leucantha ‘Santa Barbara’ (EuroAmerican Propagators). This one received arelatively low rating but is an excellent plant. The problem is that in Florida”perennial” salvias flower early and then rest until fall bringscooler nights. So as I write this, this salvia is in full bloom with lavendermasses of flowers covering a 4 1/2-foot mass of gray foliage. As with all theperennial salvias, the secret in the South is knowing when their season is soyou can produce them on schedule.

Stemodia tomentosa(RobRick Nursery). Stemodia is a little-known crop with a lot of potential forthe landscape. Similar to ‘Blue Daze’ in its gray foliage, this non-flowering(OK, it does flower, but they are so small and pale, the effect isnon-flowering) accent plant is heat- and drought-tolerant, spreading and prettymuch trouble-free. Also makes a good component plant in mixed containers. Consistenthigh evaluations for foliage quality and impact.

Tecoma stans(RobRick Nursery). Also sold as esperanza or Texas star, this relative of capehoneysuckle has been in bloom since May, is free-branching, has large clustersof 3-inch tubular yellow flowers and shows no insect or disease problems. Verystrong, drought-tolerant and easy for growers and landscapers.

Calibrachoa

This group is still growing, and we will be doing an evenlarger production trial in spring 2003. Since calibrachoas have a lot of newgenetics, there is a lot of variability in the group. We ended this trial onweek 30 when it became obvious the plants were not going to re-bloom. Everyentry in the trial had at least two good weeks of high ratings, but only earlyin the season.

Million Bells Cherry Pink (EuroAmerican Propagators) was the top performer this year. Thiscultivar just kept blooming longer, repeated stronger and had more color impactthan the rest of the trialed cultivars.

Spring Fling Yellow(HMA) and Million Bells Terra Cotta(EuroAmerican Propagators) were earliest to flower in the field. Peak floweringwas less easily determined, as varieties flushed, then re-bloomed at a laterdate. This is part of the reason the Million Bells Cherry Pink stood out soclearly.

Milky Blue Calibrachoa(Twyford Laboratories) is an entirely different form of calibrachoa, withextremely small leaves and flowers about three-fouths of an inch in diameter.While this plant was very vigorous, it did not have the color impact of some ofthe larger-flowered forms. Still, put on a good display.

Cuphea

We trialed a selection of vegetative-type and seed-produced(USDA Iowa) varieties and really enjoyed watching this diverse group of plantsperform over the season. Seed types in general had too few flowers forcommercial purposes, but there were some strong plants nonetheless. Thevegetative types clearly outperformed on a season-long basis.

Cuphea ignea(Hatchett Creek Farms). This form of Cuphea ignea was in bloom at planting andis still stopping visitors to the gardens. One-inch orange blooms on a 4- to5-foot plant. Uniform, continuous flowering, very nice.

Some of the more interesting species trialed from USDA thatdid well and are in some cases coming back strong in fall include : C. glutinosa,C. procumbens, C. racemosa, C. schumanii and C. varia.

Vegetative Torenia

I don’t think anyone is surprised at the success of thiscrop. It is continually in flower, makes a great basket, and even a novicegrower can enjoy success with it. What surprised me was the fact that they alsodo extremely well in full sun in the landscape, but they are notdrought-tolerant so keep the water coming for best growth. Every torenia entryon our gardens has held a perfect 5 rating for most of the season, and they arestill doing great. The blue forms are all excellent, but there was littlecommercial difference between them.

Amethyst Wave(EuroAmerican Propagators, Suntory/Jackson & Perkins). Definitely the mostvigorous of the colors available — strong, consistent, continuous flowering.Received the highest ratings of the group. Good size blooms and good foliagecolor.

Pink Moon (HMA).I’ve been hoping this color would get out and Pink Moon is a good variety.Extremely large flowers, moderately vigorous. We have a sport of Summer WaveBlue that we call ‘Milton Mauve’ that is also in the gardens, but the flowersare smaller and the growth more vigorous. Hopefully we’ll be able to get bothtraits into the pink color in the future. A great addition to the crop.

Verbena

All entries had 2-3 weeks of strong ratings, but theirseason of flower is really January or February this far south, so a lot of theearliest varieties were at peak flower when planted. There is a lot ofvariability, but four varieties were still surviving and blooming in thegardens here in September; they aren’t pretty, but they are surviving. Thetrial ended on week 26 for most cultivars.

Rainbow Carpet Rose(Bodger Botanicals). This variety has been in bloom all summer and is still inbloom. A good semi-upright habit, a strong color that doesn’t fade in the heatand the ability to have powdery mildew but continue flowering. Very strong.

Aztec Pink Magic(Ball FloraPlant). Another fantastic performer for the early season, this washands down the most vigorous verbena in the trial, and peak flowering was asolid mass of pale pink flowers. Medium-textured foliage, good diseaseresistance. This was a very good cultivar.

Tapiens Blue Violet(EuroAmerican). Also good, long-flowering, but foliage tended to yellow a bitand flowers faded in the heat. Still, it put on a long and attractive show.

Escapade Red(Goldsmith Plants). This variety was still flowering heavily in September. Thefoliage looked horrible, but the vigor was certainly there.

Napoleon & Sparkler series (Bodger Botanicals). These honorable mention verbena were so earlythat they were past peak flowering by the time we got them into the ground, sotheir ratings are very low. They are also unlikely to repeat bloom with anyvigor. So here are some to keep very cool and start very early, not good in aSouthern spring production scenario.

Rick Schoellhorn

Rick Schoellhorn is assistant professor of floriculture at the University of Florida, Gainesville, Fla. He can be reached by phone at (352) 392-1831 or E-mail at rksch@ifas.ufl.edu.



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