A Plant’s Perspective on This Winter
Kyle Daniel, Nursery & Landscape Outreach Specialist, Department of Horticulture & Landscape Architecture, Purdue University
This winter has held a long, cold grip on the Midwest and eastern part of the country so far this year. Even southern states down to southeastern Texas, Louisiana, and others haven’t been spared from the record cold temperatures. In January, the temperatures were -10’s, with wind chill values were recorded at -53 F in Lafayette, IN. With all of these freezing temperatures, many people are concerned with the negative effect on plants. For the most part, there shouldn’t be much damage to plant materials. Plants that are marginally cold hardy to your specific location could incur some damage, including dieback to the ground, such as crape myrtle. In recent years, these marginal plants survived the winter due to mild winters, but expect possible damage this spring. Also, plants that have been stressed due to abiotic (non-living) or biotic (living) factors could exhibit some damage due to the abnormally cold temperatures this year.
The cold weather could indirectly cause notable damage due to the copious amounts of salt and other chemical treatments applied to roadways, sidewalks, and parking lots. Since the temperatures have stayed cold enough for several snowfall events to pile on these areas, road chemicals are thus being piled into landscapes and parking islands (Fig. 1). Plants that are sensitive to salt, for example Taxus spp., will most likely sustain some amount of damage in 2014. Salt damage resembles drought symptoms or root damage. To mitigate this, rainfall or irrigation has been shown to be able to leach some of these products to minimize their effects on plants.
Plants that have evolved in temperate zone climates, such as the Midwest, use various methods to overcome freezing temperatures. The primary strategy utilized for deciduous plants is the process of dormancy. When dormancy begins in the late summer and into the fall, the plant is preparing for cold temperatures. This is accomplished via short days and cool temperatures. After the plant becomes dormant, a specific number of chilling hours must occur before the plant will begin growth in the spring. It is during this endo-dormancy period that a plant is the most cold hardy of the season (Fig. 2). The cold temperatures that the Midwest experienced have been during this period of maximum cold hardiness, so little damage is to be expected to normally ‘healthy’ plants.
Plants have processes that to contribute to cold tolerance. Included in these processes are mechanical and chemical in nature. Mechanical processes, such as evacuating water from intracellular to intercellular (inside to outside) the cell to prevent ice formation that damages the cell, are a part of what is regarded as super-cooling. This process, in turn, will increase the amount of solutes, including salts, within the cell. This decreases the freezing point within the cell, thus limiting the amount of intracellular freezing and the amount of damage to the plant as a whole. Plants produce chemicals, such as phenolic compounds, which contribute to cold hardiness via the production of suberin, tannins, and other products. Also, some hormones help regulate both mechanical and chemical changes in the plant that contribute to protection.
Most plants are most cold hardy in the buds, which is where the actively dividing cells will begin to grow in the spring (Fig. 3). In cold hardy plants, the buds can survive through extremely low temperatures. Due to the plants being at maximum cold hardiness, this cold weather streak we have experienced should not cause adverse effects on plants. Expect normal bud break this spring with few issues.
Kyle Daniel is the Nursery and Landscape Outreach Specialist in the Department of Horticulture and Landscape Architecture at Purdue University. He can be reached at firstname.lastname@example.org. Check for updates to our website for the Nursery and Landscape Industry and the Purdue Nursery and Landscape Extension on Facebook.
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Figure 1: Snow piling up in landscapes and parking lot islands most likely contain salt or other ice melting chemicals. This could affect plants in 2014.
Figure 2: The cold hardiness of temperate deciduous plants at the beginning of dormancy, during dormancy, and at bud break. The plant is most cold hardy during the winter.
Figure 3: Two buds from Gingko biloba taken in late January 2014. Notice the green tissue of the vertically dissected sample in the apical end of the buds, which illustrates the lack of cold injury.