New Guinea Impatiens Landscape Trials, 1994-1995 Summary.
William B. Miller, Russell Smith, Millie Williams, Roger Davis, and Kelly Petoskey Department of Horticulture, Clemson University

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Introduction

In the summers of 1994 and 1995, we conducted landscape evaluations of a large number of New Guinea Impatiens cultivars at the South Carolina Botanical Garden on the Clemson University campus. Our objective was to see if this crop would withstand full sun conditions in the south and whether particular cultivars would excel (survive??!) under these conditions. We found that many cultivars do possess excellent full sun landscape characteristics, and also identified a number of cultivars that exhibited consistently poor performance.

Materials and Methods

Rooted cuttings were received between late February and late-March from commercial suppliers and immediately planted into 4-1/2" pots with Fafard 3B. Plants were irrigated with clear water for the first 2-3 weeks after planting, then fed with 200 ppm N from 20-10-20. In the third week of May, 1994 and 1995, 8 plants of each variety were planted (approximately 18" on center) into beds at the SC Botanical Garden in Clemson SC. All plots were in full sun for the majority of the day, there are no artifical shade applied. Bed preparation included rototilling to 6" deep and incorporating about 2-4 inches of rotted leaves. Beds were irrigated daily with microsprinklers. This is especially critical in the first 2-3 weeks after planting until roots grow into the bed. Beds received a broadcast application of 17-17-17 slow release fertilizer (2# N/1000 sq. ft., early June) and a surflan application for summer preemergent weed control. Roundup was occasionally spot sprayed in the summer.

Evaluations of leaf quality and flower display occurred at approximately weekly intervals throughout the summer and are reported in the main table following. In 1994, ratings were given on a scale of 1 to 5 (5 best), and a rating of -1 given to cultivars not flowering at the time of evaluation. In 1995, ratings were given on a scale of 1 to 5, but the rating of -1 for non-flowering plants was not used, thus in 1995 low end ratings are a little higher than corresponding ratings in 1994. In general, all varieties showed good foliage characteristics early in the season, but transplant shock, early hot weather, and early water stress all took their tolls. All cultivars demonstrated increasingly higher quality foliage by mid-season. By the end of the season, all cultivars consistently ranked above 4.0 in foliar quality, and we have not included detailed ratings on leaf quality because all cultivars were of high quality.

Results and Discussion

Table 1 lists all cultivars, sorted by series, and their raw evaluation data throughout the summer for 1994. Perusal of this table brings out an important aspect of New Guinea Impatiens: that flowering tends to be delayed or inhibited with high night temperatures. There were large differences between cultivars in their heat tolerance and ability or tendency to remain in flower during the summer heat. To bring out cultivar differences, we averaged weekly flower ratings for the hottest months of July and August, and came up with an overall "Summer Flower Rating" that is given for each cultivar and hottest and more stressful months, namely July and August.

In Table 2, the cultivars with the highest Summer Flower Rating (in 1994) are listed along with their corresponding 1995 ratings. Conversely, 1994's poorest performing cultivars, in terms of flower display in July and August, are listed in Table 3 along with their 1995 average. Table 5 lists all cultivars, their flower and leaf colors, 1994 height, and summer flower rating in descending order of Summer Flower Rating for 1994. Tables are arranged on the basis of 1994 data because a greater number of cultivars were available in 1994 than in 1995.

Acknowledgments

We thank Ball Flora Plant, Fischer Geraniums USA, Inc., Mikkelsens, Inc., PanAmerican Seed Co., and Paul Ecke Ranch for donating the plant materials used in these trials: Fafard, Inc. for media donations, and the South Carolina Botanical Garden for landscape bed space.

Last Updated 8/3/98