by Lydia Holley November 8, 2021
Have you ever wondered why it is often recommended to plant shrubs and trees in the fall in Texas? Here’s the answer: soil temperature affects root growth.
Ideally, a plant should grow roots that are not only long but also thick, with numerous offshoots. This gives the plant the most root surface in order to take up water and nutrients. If the soil temperature is too high or too low, root growth will suffer, sometimes to the point of causing the plant’s death.
What is the perfect soil temperature? There are numerous species of plants, and they each have certain zones they prefer to grow in, as well as various life spans, such as annuals or perennials. Some warm weather vegetables do not grow well until the soil temperatures reach 70 degrees F, and start to die in soils below 55. That is why these annuals are planted in spring as the soil temperature rises.
For most shrubs and trees, however, soil temperatures from 40 to 65 degrees is best, with around 60 being optimal. In general, our soils seem to hold that range of temperatures in autumn for some time, long enough for shrubs and trees to get some good root growth going before the soil cools too much. Part of the reason root growth does so well in those temperatures is that the temperatures are too low for a lot of shoot growth. Thus, the plant can dedicate all its energy to its roots. But as autumn fades into winter, soil temperatures will eventually get too cold. For most shrubs and trees, root growth slows in soil temperatures below 40. If you plant in autumn, they get optimal root growth now and later on in spring before the temperatures rise too high.
How do you know your soil’s temperature? The only way to tell is to measure it. You can do this with a regular thermometer. Put it in the soil to a depth of at least four inches and let it stay for a minimum of five minutes. You should be able to get a fairly good reading.
So, if you’re wondering whether to plant trees and shrubs now, the answer is yes. And now you know that the reason behind the recommendation to plant shrubs and trees in autumn is because of soil temperatures for optimal root growth.
Henderson County Master Gardener Association provides multiple resources at its website: https://txmg.org/hendersonmg/ or direct questions by calling the county extension office at 903-675-6130.
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