How can potted plants tolerate our extreme temperatures?
The answer: Root systems in pots have a restricted amount of soil. However, that soil retains water, and given ample water on a regular basis, and a large-enough pot, some plants will often be OK.
The key word is “some.” When there is an abundance of surface area on leaves—where moisture is pulled out by the heat—water is depleted at a rate faster than the roots can take up water. In other words: You should not assume that a wilting plant is due to a lack of water. It may be that the plant cannot keep up with the drying rate through the leaves.
Choosing the right plants, larger pots and providing shade will help solve this problem.
A popular plant such as Ipomoea batatas—sweet potato vine (pictured above)—has broad leaves which grow quickly and cover much of the pot and even ground areas, thereby exposing it to fast rates of transpiration. Even if the soil in the pot is moist from a daily watering, there is no way the plant can keep up. Summer plants and flowers with smaller leaf structures will do better in our desert conditions. Salvias, pentas and vincas are three of our most-reliable summer flowers.
The term drought-tolerant is used to describe plants that will grow well with little, if any, supplemental water, like the bougainvillea with vinca, pictured below. Key to that description is that the plant will be drought-tolerant once established.
The first year is critical as the roots develop and become acclimated to the temperatures, soil, water and living environment. The roots cannot be allowed to dry out during this crucial time of growth. When you see new growth in the stems and leaves, you will know that the roots have developed sufficiently to change the frequency of water. As always, be sure to water deeply each time.
Still, I know of no summer flowering annual that can truly be called “drought-tolerant” in the desert. These plants will still need regular watering, which typically translates into daily. In other climates, some flowers might be called “drought-tolerant” or “low water”—but in the desert, don’t believe it!
Marylee is the Desert’s Potted Garden Expert. Email her with comments and questions at firstname.lastname@example.org.