Green Thumb – Flowers of the Frost

Posted: September 18, 2019

Fall is often the forgotten gardening season. However, fall is one of the most beautiful of the seasons in nature and can be equally amazing in our home gardens. There exists a good selection of plants that do well in the fall and right up to the time when frost begins to appear.

An understanding of frost in northern Illinois will help us with our garden planning. In a typical year, frost arrival dates can be anywhere between Oct. 5 to Oct.15.

There are two types of frost events. Early season frosts are usually radiation frosts. Cool air from Canada accompanied by light winds and clear skies will cause this type of frost to form. Advection frosts, occurring later in the season, are the result of deep, cold air masses arriving from Canada and quickly plunging temperatures into the 20’s. This second category of frosts will kill most non-hardy vegetation.

As gardeners, we know that as frost season sets in, we will lose a large majority of our plants. However. we can now get creative with those hardy plants that will be able to tolerate early frosts. We will turn to anemones, asters, mums and sedums to spice up our fall gardens.

Fall anemones are large, attractive plants. Japanese anemone is a beautiful plant that grows from a cluster of maple-shaped leaves near the ground. The anemone then sends up a series of long, wiry stems topped with delicate, cup-shaped flowers. Profusely blooming from late July into October, anemones occur in attractive colors or white, pink, rose or lilac.

Asters come alive during the fall months. They will produce the most successful fall bloom period if they have been pinched back a couple of times during the growing season. Pinching back creates a much fuller plant which then blooms in the fall when other plants have stopped growing. The aster plants can grow from 2 to 6 feet depending on the variety. Color options include white, blue, lavender, pink and rose.

Chrysanthemums are perhaps the most famous of the hardy fall plants that tolerate cold temperatures and frosts. Mums should be planted in the spring to allow for good root development. Pinching back for mums should be completed by July 15. Two tips for successfully wintering them over include leaving the dead stems in place and mounding up dirt at the base of the plant. My mums always succumbed to winter kill until I tried the above tips. They have now been growing and thriving for the last three years. These tips really work.

The last of the recommended perennial plants for cold toughness is the sedum family. ‘Autumn Joy’ sedum holds the record for the most frequently used of the fall sedums. Its large, versatile blooms transform from lime green, to pink to dark rose as temperatures cool. This is certainly a plant that is major “bang for your buck.” There are, however, many other attractive sedums that also tolerate the cold well. ‘Matrona’ is a newer more medium sized sedum. In contrast to its beautiful pink blossoms, the stems are a striking, dark burgundy.

Not to be out done by the perennials, the annuals would like to offer a couple of fun plants with very good cold tolerance. Pansies and violas would like to put in a bid for attention. New varieties of these old time favorites have been hybridized to withstand extreme cold temperatures. More colors and varieties are being introduced every year and can be found at the nurseries often with ‘Polar’ of ‘Icicle’ as part of their name. These  plants for fall gardens usually appear at garden centers in late August or early September.  Little pansies and violas look great in planters or containers.

The threat of cold weather does not have to signal the end of the garden season. With the use of cold tolerant plants, we can put on a vibrant autumn display and extend the pleasure of time working in our gardens.

Barb Lindholm – University of Illinois Extension, DeKalb County Master Gardener

 

GOT A GARDENING QUESTION?

Submit your questions to connections@dekalbfarmbureau.org. or call the University of Illinois Extension Horticulture Help Desk at 815-758-8194.


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