Technical Information Bulletin

SUBJECT: Unique Characteristics of Dark Leaf Poinsettia Cultivars

The poinsettia has been the focus of years of research by various universities and growers. The information accumulated from these efforts has helped our industry understand the needs of our crop at each stage of production. Technology and information continue to evolve, challenging growers to keep up with the pace of change.

As new cultivars are introduced, it is important to adapt and change cultural practices accordingly. One of the more dramatic transitions in production has occurred during the past 5 years as growers have moved to cultivars with characteristic dark, green leaves. Dark leaf cultivars react differently to conventional production practices and exhibit some unique growth responses. In order to be successful, growers should recognize the need to institute changes in cultural regimes. Some of the responses outlined here are generalizations and may not apply to all of the cultivars in this group.

Branching: Lack of consistent branching was common with the first dark leaf cultivars, however this is not as significant with more recent introductions. When stock plants for cuttings of Eckespoint^® Lilo, Lemon Drop, or Red Sails are exposed to continuous daytime temperatures greater than 85°F/29°C, auxiliary shoots abort or fail to develop after pinching. Care must be given to maintain cooler, darker growing conditions for stock to preserve branching potential of resulting plants. Growers have also found that young rooted cuttings develop more uniform branching when soft pinch and leaf removal technique is used to initiate branching. All poinsettia cultivars react favorably to this cultural procedure.

Fertilization: An appealing characteristic of dark leaf poinsettias is the appearance of healthy looking foliage, even when grown with low fertility regimes. Research conducted during recent years substantiates this observation. At Pennsylvania State University, Mary Ann Rose studied nitrogen use, recovery and growth analysis of the poinsettia. Her work documented differences in plant growth efficiency of Lilo and Eckespoint^® Celebrate 2. Lilo produced higher quality plants than Celebrate 2 when grown at CLF levels of 100 ppm or less due to its rate of nitrogen (N) uptake. These plants also showed higher nitrogen recovery efficiency from the plant structures. When comparing the cultivars Lilo and Annette Hegg^TM Dark Red, Erling Strømme of the Agricultural University of Norway documented differences in absorption of elements, such as phosphorus (P). Researchers studying bract necrosis, now referred to as bract edge burn, identified more active uptake of potassium (K) by cultivars such as Lilo, and recommend a reduction of this fertilizer during bract development to minimize induced calcium deficiencies leading to bract edge burn. Although additional research is needed to include a wider selection of poinsettia cultivars, the dark leaf cultivars as a group have proven to use nutrients more efficiently. It is believed that this group requires about 20% less total feed than the other, medium green leaf cultivars.

Foliage Abnormalities: Leaf deformity is likely to occur on dark leaf cultivars grown under higher light intensities, temperatures or other stress inducing conditions. The dark leaf pigmentation of these cultivars collects and traps more light and heat energy resulting in changes in leaf temperature and tissue growth. The cultivars Lilo, Lemon Drop, and Red Sails develop a blistered leaf surface and chlorosis (both marginal and interveinal) when exposed to high light (5000+ foot-candles/52,300+ lux) and air temperatures above 85°F/29°C. Eckespoint^® Freedom^TM exhibits a unique leaf curl and dehydration when exposed to rapid changes in the environmental conditions. This reaction is most likely to occur under sudden fluctuations of temperature or light intensities and when the growing medium is allowed to dry. Damage is usually limited to only a few leaves, but symptoms occur rapidly without warning. This abnormality does not result in a significant loss of value for the finished product, as it does not continue to progress onto other leaves of the affected plant.

Internode Stretch: Dark leaf cultivars have a tendency to stretch during the finishing stages of bract expansion. This increase of internode length between transitional bracts and the primary bracts has occurred in response to warm finishing temperatures and as fertilizer levels are lowered during November. With the reduction of fertilizer applications, the soluble salt (EC) concentration in the medium will begin to drop and allow for an increase in water uptake. Reports of late internode stretch have been fewer from growers using lower total fertilization program throughout the crop (150 to 200 ppm N only) than from growers with higher feed levels (250+ ppm N). Regular clear water applications can help to minimize the potential late stretch and can even be used to encourage growth earlier in the production cycle. Growers should anticipate potential late stretch of these plants when fertilizer programs are adjusted for finishing and when the fall growing conditions are warmer than normal for the area. Given the wide consumer and grower demand for the dark leaf poinsettia cultivars, breeders continue to focus their efforts in this direction. Currently, dark leaf poinsettias are available commercially in a range of red, white, pink, and novelty colors.

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