As I am writing this column I glanced at my weather app on my phone and it has no rain chances for at least the next 10 days. It’s important for trees, shrubs, turf and perennials to go through fall and into winter with a moist soil. Since we’ve had an extremely dry period, it is a good idea to thoroughly water young trees, shrubs, and evergreens before the soil freezes. It won’t hurt to water your large established trees too.
Roots do not go dormant as quickly as the above growth. While the tops of plants go dormant or stop growing as it cools down, roots continue to grow throughout the fall and even into December if the soil temperatures are warm enough.
To encourage fall root growth, provide adequate moisture until the soil freezes. Check the soil around your trees. If the top few inches are dry, moisture is needed. For trees and shrubs, moisten the soil to a depth of eight to 12 inches or more while taking care not to overwater. Lawn grass only requires about six to eight inches of moist soil going into the winter.
A long screwdriver is an excellent tool to measure soil moisture. If you can push the screwdriver into the soil easily, this indicates the soil is moist. However, if you can still push the screwdriver in but meet resistance, this indicates the soil is dry. After a rain, it may be easy to push a screwdriver in the soil a few inches, then becomes more difficult. This indicates how far the rain infiltrated into the soil.
Keep in mind roots are less cold hardy than stems. Roots surrounded by moist soil are less likely to suffer cold temperature injury because moist soil holds more heat than dry soil. Frost penetration is deeper and soil temperatures are colder in sandy or dry soils.
When twigs and stems die in a tree or shrub, we are aware it’s happening. When roots die, we cannot see the dead roots and are not aware roots are dying. This could be one explanation why one tree establishes quickly while another is slow to establish or dies.
Plants going into winter with adequate fall moisture are also less likely to suffer damage from winter drying. Plant tissue, particularly the green needles of evergreens, can lose moisture during winter. Most moisture is lost on warm, sunny, windy winter days.
Moisture lost from plants during winter cannot be replaced by the roots, either because the soil is frozen or because roots do not function at soil temperatures below 40 degrees F. This is why fall moisture, either from rain or irrigation, is important.
When woody plants go into winter water stressed, their tissue can be killed by winter drying. This is easy to see on evergreens when needle tips, or entire branches turn brown in late spring. Some evergreens survive and new growth covers up the damaged growth. Other evergreens are killed by winter desiccation.
The leaf and flower buds on deciduous plants, those that drop their leaves, as well as small twigs on woody ornamentals may be killed by winter desiccation. This can result in sparse flowering or leafing. Plants may be forced to produce secondary buds which uses stored food within the plant and may lead to stress.
So, keep the soil around trees, shrubs, turf and perennials moist up until the soil freezes and water if necessary. A good way to water trees and shrubs is to take a soaker hose and lay it upside down around the dripline or tips of where the branches extend because this is where most of the roots that take up water are located. Building a water-holding dike several feet away from the trunk does little to meet that tree’s soil moisture needs. The large roots near the trunk provide stability, but take up very little water or nutrients.
If dry conditions continue into late fall, irrigation can continue monthly from October through December or until the ground freezes.
Mulch trees and shrubs with a two to four inch layer of wood chip mulch to help conserve soil moisture. Keep the mulch a foot away from the trunk to avoid voles making a home in the mulch and gnawing on the trunk. It’s also important mulch layers are not too deep. Roots that grow into the mulch will be killed by cold winter temperatures, further stressing a tree.
