After several years of warm winters, it appears that we are in for a cold winter. The benefit of the cooler period is that it will allow plants time to hibernate, result in greater vigor in the following spring as well as reducing the pest population.
The downside is that the cold weather requires winterization of our yards and protection of tender plants, particularly the tropicals that are such a key component in many of our Houston landscapes. The following is a refresher on how to prepare your garden for a freeze and which plants need special attention.
Types of Cold and Plant Hardiness
As we enter the winter months, keeping an eye on projected temperatures is important. The cooling temperatures we have experienced over the past month is actually beneficial for the plants as it has allowed them time to adjust and harden against the cold weather. Cold snaps that come suddenly are more harmful as the plants have not had this hardening off period and cause more shock and damage to plants, especially those that are tender. (( Dan Gill. Cold Protection in the Louisiana Landscape: Ornamentals and Vegetables. LSU Ag Center. 23-1-2014. Accessed 18-11-2014. ))
Freezes that come through an overall lowering of temperatures (radiational freezes) are less harmful to plants than cold fronts (advective freezes) that move in with strong winds and cause a sharp drop in temperatures. The Houston area does not often bear the brunt of these cold fronts as other areas of Texas do. However, watching weather projections is always a good idea. In one unexpected freeze last winter, we lost a number of our plants at the Garden Center as we didn’t have time to prepare.
Note: While wind chill plays a role in our own comfort and ability to stand the cold, a plant’s cold hardiness is determined by the actual temperature without the wind chill factored in. (( Faith Brown. How to Protect Plants from Frost. Marin Master Gardeners. University of California. Accessed 18-11-2014 http://ucanr.edu/sites/MarinMG/Marin_Master_Gardener_Help_Desk/Leaflet/How_to_protect_plants_from_frost/ ))
The other important factor to be aware of is the level of hardiness of the plants in your landscape. Preparing for a freeze is much easier when plant hardiness is taken into consideration during landscape planning. Tender plants have a better chance of surviving the cold when they are planted in areas blocked from the North wind and in sheltered areas.
Tender plants are those that will not survive temperatures below 32 degrees. Hardy plants will survive temperatures below freezing; however, there are degrees of hardiness. For example, among citrus trees, Satsuma orange trees are hardier surviving to 20 degrees while lemon, lime, and orange trees are only hardy to 26 degrees. Most trees, shrubs, and ground covers will survive to 10 to 15 degrees. (( Seasonal Advice / Monthly Checklists: Nov-Dec. Collin County Master Gardeners. Texas A&M AgriLife Extension Service, Collin County. Accesed 18-11-2014. http://www.ccmgatx.org/gardening-resources/monthly-garden-checklists.aspx ))
Helpful Tip: Keep track of the cold hardiness, blooming periods and sun requirements of the plants in your landscape. After purchasing a new plant, staple the plant information tag to an 8 ½ x 11 sheet of paper and make a note of the date and place purchased. Put the sheets in a 3 ring binder and make notes on plant performance, treatment, and care.
For specific information on plant hardiness, visit the LSU Ag Center for a listing of plants commonly used in Gulf area gardens and their cold hardiness.
Frost Protection Starts in Preparation
One of the key defenses in protecting your plants from freeze damage is good plant health. Prepare your plants to weather the cold by providing proper nutrition through the summer months and keeping the plants and soil free of insects and disease.
Hardy trees and shrubs should not be pruned or fertilized after September. Both encourage new growth, which will make the plant more susceptible to frost damage. Oil sprays, such as those used on citrus trees, should not be used after August 15th.
Preparing Plants for a Freeze
Water: Water the ground to prevent the ground from drying out. A plant with proper moisture will withstand freeze damage better than one without.
Container Plants: Move small container plants and hanging baskets indoors to protect from cold. Group any container plants left outdoor together and cover with a frost blanket.
Mulch: Mulch around the base of trees and shrubs with pine straw or leaves. Also cover nonblooming tubers, bulbs, and rhizomes to prevent from freezing.
Cover: Cover plants.
Trees: Wrap the trunks of tender trees. Prevent against foliage damage by stringing trees with Christmas lights.
Fruits & Vegetables: Harvest any mature fruits and vegetables.
After the Freeze
- Remove plant covers. If covered with plastic, it can stay in place if vented so plants can breathe. Fabric covers can remain in place for several days, but then will need to be removed so the plants can get light.
- Do not prune or remove any frost damage for a week after the freeze. Some frost damage does not appear immediately.
Tropicals: As a tender plant, tropicals are especially susceptible to frost damage. Mulch well and cover the plant prior to the freeze. If the cold is going to be severe, surround the tropicals with support, string Christmas lights on the supports and cover. If the tropicals do get damaged by frost, most of the time they will grow back from the root as long as the ground itself did not freeze.
Banana Trees: Mulch around the base of the tree. Wrap up the trunk of the tree to where the leaves start. Cover if possible. After frost, remove any damaged leaves. If the tree had fruit the previous season, trim all the way to the ground..
Citrus Trees: Harvest all ripe fruit prior to the freeze. The fruit will freeze before the tree does. Mulch around the base of the tree, wrap the trunk of the tree coating first with copper fungicide. String trees with Christmas lights and cover if possible. The older the citrus tree, the hardier it will become to cold damage. Keep the soil moist to provide a barrier against cold.
Types of Cold Protection
Covers: Plants can be covered by a variety of materials. Plastic and fabric, such as old sheets, are frequently used. We carry frost blankets at the Garden Center. If covering with plastic, the plastic will need to be draped on supports rather than the plants themselves. Any foliage touching the plastic itself will freeze. Also, the plastic will need to be either removed or vented during the day to allow plants to breathe. Small plants and shrubs can be covered with Styrofoam or cardboard boxes.
Wraps: The trunks of tender trees can be wrapped with bubble wrap, foam rubber, or blankets.