Tucson's winter weather extremes, especially hard frosts, can be quite damaging to our plants, trees, flowers and planted gardens. Simple precautions can make a huge difference in their life and reemergence this Spring.
Please take a moment to read this short e-newsletter. You'll be glad you did! If you have any questions, or need for professional assistance, our knowledgeable Sonoran Gardens' team is just a call away at 520-579-9411.
Understanding a Plant's Response to Cold by Charlee Ware, Kingman Area Master Gardener, University of Arizona
Your plants' species, age, water content, general health, and stage of growth determines their reaction to cold temperatures. Young, actively growing, flowering, and/or dehydrated plants tend to be most vulnerable to freezing temperatures. New growth on older plants, which were heavily pruned, and/or fertilized in late summer or fall, is also at risk.
Winter hardy plants need winter acclimation, which begins with the shortening autumn days. Second, plants need the lowering temperatures to result in full hardiness and acclimation. If a hard freeze occurs when there has been no prior cold weather to "harden off" the plant tissue, damage will be more extensive.
The faster the temperature drops, the lower the temperature, and the longer the temperature stays low, the greater the damage to plants. For example, a short 15 minutes at 15-degrees, may cause less plant damage than an hour at 20-degrees.
There are three periods each year when plants are at their biggest risk for heavy frost damage:
- Early fall, before plants acclimatize
- Or, during very cold temperatures after a week or two of warm winter weather. For example: when temperatures have been close to average for weeks, and then suddenly drop 15-20 degrees for several days.
- Plants can also experience heavy frost damage in late spring, after the warming weather causes new growth to begin, and fruit trees to bloom. While the trees are cold hardy, the new growth, blooms and tiny young fruit aren't.
Understanding Methods to Prevent Severe Frost Damage
- Potted plants: The safest option is to move the plant indoors for the winter, either into the house or a greenhouse. A variance of this idea is to give them wheels—moved indoors (usually a garage) at night and outdoors on most days.
- Plants & trees: some simple winter maintenance will help to lessen frost damage:
- During late summer and fall, do not fertilize plants. Newer growth damages easily.
- During winter, continue to deep water your trees and shrubs monthly, and evergreens twice monthly. Hydrated plants survive better.
- Keep the surrounding area free from weeds, lawns, and organic mulches during the winter. They absorb less solar radiation than bare or gravel mulched soil, thus there is less heat to reradiate at night.
- If you purchased bare root roses and have planted them in pots, it is best to move them to a protected area if the weather gets below freezing. All established roses that are in the ground require no winter protection in AZ.
When a heavy freeze is expected, be prepared with a few actions to protect them further:
- Water the plants well the morning before possible frost/freeze.
- Cover frost susceptible plants will old packing blankets or sheets. You may need to sew several together. Do not use plastic or landscape mesh. See sketch below for the correct way to cover. The cover must go to the ground, as you will be trapping the earth's heat under the blanket. Use several bricks or rocks to hold it down. All covers must be removed during the day.
- If you still have your holiday lights up, leave them on and near the bottom portion of plants until late spring, or have available out-door/weather-proof lights and extension cords. These go under the blanket near the ground. You can set on a rock or brick. Use extreme caution the light doesn't touch the cover or plant materials.
- Cardboard boxes work on smaller plants. Again, use a brick or rock to weight them in place.
- Use styrofoam cups on columnar cactus tips.
- Instead of covering, use overhead sprinklers to form ice around buds, which, strange as it sounds, keeps the temperature in the buds around 32-degrees. This is often used on fruit trees when frost threatens during or after flowering.
Understanding what to do if a plant is frost damaged:
- MOST importantly: DO NOT PRUNE! Wait until the plant begins growth in late spring. Branches may appear damaged, yet some will recover come spring. In addition, pruning too early, may stimulate new growth that then becomes susceptible to late frosts. Damaged leaves and branches remaining on the plant also help to trap warm air close to the plant.
- Palm Trees: if a palm tree is damaged, check the bud at the top. If there is any mushy tissue, remove all that you can, and give the growth center a disinfectant wash with a copper-based fungicide spray. Sonoran Gardens can do this for you. Unless mushy, leave all browned fronds on the plant. In any case, don't give up on it too soon. An injured palm may need both spring and summer to begin recovery.
By simply following these easy steps, your flowers, plants and trees will be strong and beautiful! Sonoran Gardens is always here to help and answer your questions. We can even help you get your plants "frost ready" and we can insulate your pipes, too.
Have a great winter!
The Sonoran Gardens Staff