Cool Season Color

May 3, 2007 - 10:28

Winter in Florida? Most people consider this a contradiction as Florida residents do not experience snow and ice like the rest of the country, but Florida does have its distinct growing seasons. We have the ability to garden 365 days of the year, but plants still must be matched to seasonal conditions.

The winter garden at the University of Florida was established with the purpose of evaluating cultivars for three main objectives: winter flowering, cold tolerance and ability to be used as a season extender. This year, cultivars were planted in the garden mid-November and evaluated every two weeks. The plant material will remain in-ground through the end of May so plants with season-extending performance can be viewed during the university’s annual Floriculture Field Days.

The main winter season in Gainesville, Fla., is from mid-November until the end of February. Average weather conditions are 65-70° F days and 45° F nights, with an average of 5-10 nights of frost and freezing temperatures. Plants used as season-extenders must be able to withstand wide temperature swings while still providing color in the landscape. Although Florida’s winter is much warmer than the rest of the country, it is typical of late spring conditions in the northern states. Plants that can survive mid 80s one day and freezing temperatures the next have the ability to be planted close to the frost-free date without concern for their survival should a late cold front push through.

Plants typically selected for winter performance include pansies, violas and snapdragons, but these crops are often overused in the landscape. Gardeners and landscapers are always looking for new and exciting cultivars that can be used in place of the old stand-bys or as companion plants. The crops highlighted in this article have been trialed in recent years by the University of Florida and are being recognized for their excellent winter performance (for a list of the 2007 Winter Trial winners, see sidebar, page 32).

 

Argyranthemum

Much breeding has been done on argyran- themum in recent years, and this crop is proving to be an important winter and spring performer. Typical cultivars available had yellow or white daisy flowers. Recent introductions have increased the color range to include all shades of yellow, pink, rose and red, and flower forms now include single daisy flowers and double pom-pom flowers.

Argyranthemum ‘Butterfly’ from Proven Winners has been trialed the past two years, and these plants can tolerate a light frost and temperatures in the high 20s with little leaf burn, but they start to show shoot burn and dieback when temperatures dip into the mid 20s with a heavy frost.

This plant can be used as a spring and summer plant for most areas of the country. However, in Florida, plants start to decline by early summer due to humidity and high disease pressure. Argyranthemum is an excellent landscape plant as well as a centerpiece for large mixed planters.

 

Chrysocephalum

A new chrysocephalum was introduced to the market last year by Proven Winners and has proven to be an exceptional landscape plant. We have grown this cultivar during both winter and summer trials, and it has been one of the best performing plants. This plant is capable of surviving the heat and humidity of Florida summers when temperatures regularly are in the 90s and the winter frosts and freezes when temperatures dip into the mid 20s with little to no tip burn.

The Flambe series contains two colors but the cultivars differ in plant habit and appearance. ‘Flambe Yellow’ is slightly more vigorous and has a better branching structure than ‘Flambe Orange’. It also has larger leaves and the foliage has better silver coloration. Both cultivars have indeterminate inflorescences that continue to flower during the entire season and require no deadheading. Plants grow 12-18 Á inches tall and provide excellent coloration in the landscape and work as accent plants in mixed baskets and containers.

 

Dianthus

Dianthus has been a favorite plant of gardeners for many years, and cultivars available on the market today provide a wide range of flower color, flower form and plant habit. This versatile plant can withstand the cooler winter temperatures as well as the heat of the summer, and many gardeners in the South have been able to keep this plant alive for multiple growing seasons.

Plants range from 12 to 30 inches tall depending on cultivar, and common colors include reds, whites, pinks, salmons, purples and bi-colors. Shorter cultivars are typically used for borders or mass plantings, while taller cultivars are used as garden accent plants or in mixed containers. The plants are generally self-cleaning because new flushes of growth and flowers cover the older inflorescences. In our 2007 winter trial, dianthus ‘Sweet Mix’ from PanAmerican Seed was recognized as one of the top performers.

 

Diascia

Diascia is a great addition to any landscape during cooler temperatures. Breeding in recent years has greatly improved the growth habit and increased the color range. Most plants have a semi-compact, mounding growth habit that works well in the landscape as well as mixed baskets and planters. The color range complements the rich colors of fall and the bright colors of spring and now includes white and shades of pink, lavender, salmon, orange and red.

Diascia ‘Wink Garnet’ from Ball FloraPlant, one of our top performers, survived temperatures down to the mid 20s in the trial garden; however, some of the flower buds froze back and the plants went colorless for two weeks until the next flush of flowers emerged.

 

Erysimum

Erysimum is a great alternative to snapdragons in a landscape. The most common colors are cream, yellow and orange. This plant is a great complement to pansies in the fall due to the bright and vibrant colors, continuous flowering and medium height in the landscape.

In our trials, plants flowered continuously during the entire growing season. While erysimum does not have a lot of heat tolerance, it can hold up through the transition period from winter to summer. This year, ‘Citrona Yellow’ from PanAmerican Seed was recognized as one of the top performers.

 

Nemesia

Nemesia makes a wonderful addition to any landscape because of its color and fragrance. The first nemesia on the market were small flowered and available in white, pink and blue. Breeding has increased both flower size and color range, such as yellows, oranges, reds and roses.

Most nemesia have an upright, mounding habit with good lateral branching. They have similar cold tolerance to diascia and can tolerate mid 20s with no plant damage, but flowers and buds are subject to damage, giving the appearance of cycling color. Nemesia are more sensitive to disease than other crops. They should not be grown wet and are best used in small plantings or containers.

 

Phlox

Phlox is an excellent performer during both the winter and summer seasons, even in the Deep South. Many phlox series have been introduced in recent years and include a wide range of colors and plant habits. The most vigorous series is Intensia from Proven Winners and the most compact series is PowerPhlox from Westhoff.

Blooms are available in white, pink, purple, red and star patterns. Breeding improvements have produced plants with a mounding habit and flowering over the entire plant. These plants have been trialed in both the winter and summer trials and have bloomed continuously during the entire season. Phlox can be grown as a groundcover in the landscape or as a component plant of mixed containers. The only caution is that phlox are sensitive to root diseases and should not be grown wet.

 

Snapdragon

Snapdragons have been around forever and are a common winter annual, but improvements have increased the use and popularity of this crop. Snapdragons are available in many plant heights, from tall garden cultivars reaching 36 inches in height, to medium landscape cultivars reaching 18-24 inches tall, to mounding and trailing cultivars reaching 8-12 inches tall. Many of the shorter cultivars do not require deadheading for repeat blooming, and the newer trailing cultivars are popular as component plants in winter mixed containers. Flowers are available in a wide range of colors to match the holidays in the fall, winter and spring seasons. One of the most eye-catching cultivars in the trials this season was snapdragon ‘Luminaire Harvest Red’ from Ball FloraPlant.

 

About The Author

Jessica Boldt is a graduate research assistant Jennifer Boldt is trial coordinator and Jim Barrett is professor of floriculture at the University of Florida, Gainesville, Fla. Jessica can be reached at jlboldt@ufl.edu.

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