It is hard to tell you exactly how to care for your plants in a newspaper column because there is more plant diversity here than a tropical rain forest.
Arizona is almost as diverse as a rain forest, but then add all the exotic plants that people and nurseries have introduced to the area, plants found growing in landscapes and yards, in pots on patios … the sheer number of species is incredible. Luckily, there are some general principles of plant care that can be applied.
No matter where your plants are from, the first line of protection from cold is also the first line of protection from heat — mulch with organic material. Plants in containers and plants in the ground can benefit from a nice thick layer of mulch. Mulching plants helps keep the soil warmer when temperatures drop by providing a cushioning layer of trapped air. Mulch also makes it easier for soil to retain moisture. Moist soil retains winter warmth better than dry soil.
There are a vast variety of mulches available. Visit your local nursery or garden center for bark mulch from hardwood or cedar bark. Composted mulch is a soil additive, not for top dressing. You can also make your own mulch.
The best mulch of all is the natural mulch Mother Nature provides. Fallen leaves and needles make lovely mulch. My two favorites are pine needles and Mexican palo verde needles. There are many older pines in our neighborhood, and people with gravel lawns that don’t like “mess.” They rake the needles into piles and I haul them off to help my plants.
Leaves from deciduous trees work well as mulch also. Rake them to where you want them, then sprinkle a fine layer of soil on top to help hold them down. Water them too, so they start to decompose and pretty much stay in place. Our mulberry and olive leaves make excellent mulch for my tropical loquat tree. Oleander leaves are toxic and should only be used to mulch oleanders.
The second line of frost defense is water. It sounds contradictory, but it’s not. Moist soil retains warmth better than dry soil (see above). By watering the soil all the way around plants that might freeze, you help raise the temperature in their frost tender area by a few degrees. This is usually enough. Do not apply water from overhead, you don’t want it on the leaves.
Due to planting in microclimates and extensive mulching, I rarely have to resort to the third line of defense, blankets. Old blankets, sheets, burlap or towels, can help keep plants warm. Mostly you are trapping in soil warmth and slowing its loss into the air. Blankets are especially needed on windy nights. Branch tips may be lost to frost, but the central portion of the plant generally remains alive.
This brings us to the last point, care of frost-damaged plants. As hard as it sounds, wait until after last frost to prune off damaged wood. Last frost is officially April 1, but it varies. Generally March 15 is fine. The worst frost damage is generally seen on bougainvillea, lantana and hibiscus. If you prune too soon, a cold spell even in the 40s can damage your plants. Leave the dead wood on the plants until spring to help hold in warmer air and protect what is left of your plants.
Give your vegetation the added boost it needs to make it through the winter season, and enjoy the cool air without worrying about the health of your plants.
Dr. Soule is currently working on a book on the herbs of Father Kino and how to grow them today. The book is scheduled to be released as part of the commemorative events surrounding the 300-year anniversary of Padre Kino’s passing. For information on the book or on classes I offer in the Tucson area, give me a call at 292-0504. Please leave a voice message.