Garden Sage: Some grasses OK for Tucson; drought to stick around

Answer: There are some native grasses that are fine for the desert and our landscapes. Extensive research has been and continues to be done to determine the best plants for our region. We even have a research operation in Tucson. It is called the United States Department of Agriculture Natural Resources Conservation Service Tucson Plant Materials Center.

You can schedule a tour if you are interested to learn more about grasses that are appropriate for our region. Google AZPMC if you want to learn more .

There are, however, other species that are invasive and should not be planted here. In some cases, these problems are self-inflicted because humans failed to see the downside to species that were once thought to be a great solution to erosion or nutrition for livestock . I like to think that nowadays we are much more careful about planting grasses that can reseed and become invasive.

Unfortunately, this only works if we are aware of the potential problems. Some grass species that are marketed as sterile are not 100 percent so and unfortunately they are popular landscape plants. I wouldn’t blame the landscape architects for all these troubles. Many of them are schooled in proper plant selection through their degrees and their experience. Part of the blame can be spread to consumers who buy the plants and nurseries that sell them.

In the end, it is something we all need to educate ourselves about when considering which plants to use no matter where we live.

Question: I just moved to Arizona from Wisconsin. Is there any indication when the drought might end or is this long-term condition due to climate change? And if it doesn’t improve, what will be the impact for places like Tucson?

Answer: The drought we are experiencing has reportedly been going on for more than 20 years with no end in sight. Climate scientists predict it will likely get worse. The big challenge in the Southwest has always been a shortage of water. Even the earliest explorers thought the region was not a great place to build towns and cities, but we humans are sometimes determined to find a way. There are many articles and books on this subject, so there is no shortage of information if you’re interested in learning more.

“Cadillac Desert” by Marc Reisner is one of the classic books on this topic. Something more current would be the CLIMAS website at the University of Arizona, climas.arizona.edu, that assesses climate in the Southwest and includes research findings, blogs, and podcasts on many aspects of climate.

Question: Please tell me when I can transplant two small agaves that I raised from the little ones off a large plant. I was thinking of doing it now that it has cooled off, but I thought it would be better to get your advice.

Answer: Agaves are easily propagated from the offsets, aka pups, or little ones as you called them. Now is a fine time to plant them. If you removed them from the parent plant by cutting the stolons (the underground branches by which they are attached), it’s a good idea to let them dry for a few days to form a callus on the cut end. Agaves do best in well-drained soil such as a mix sold for cacti and succulents. You can simply push them into the soil, although they might get a better start if you put them in a container in a shady area until they establish roots.

The root establishment can take up to four weeks. Once rooted, they will start growing and then you can apply a soluble fertilizer, but only once or twice per year. Watering should be done as often as the container dries out. It’s not great for them to stay wet all the time, so allow the soil to dry between watering. If you eventually transplant them into the ground, watering should be done less frequently. In the summer, water every 10 to 14 days unless there was rain. In the spring and fall, every three to four weeks and none in the winter.

Question: We have several acacia trees that are about 12 years old. Our landscaper had described them as sweetgum acacia, but I am not sure if that is really what we have. They have grown up from an initial height of 5 feet to 15, but they are not looking healthy. Especially over the last five years, the leaves have gotten very sparse and they are often covered with small, white insects. Some of the branches have died and have no leaves at all. Our landscaper has repeatedly sprayed them with pesticide, but the white insects always return. These trees are irrigated with a drip system. Other neighbors all across Oro Valley seem to have the same problem . Also on our property we have other native acacias, which we did not plant and they are doing fine. They have the small orange-yellow colored balls and they have never been sprayed and they are not even irrigated. Should I just give up on these trees and replace them with mesquites, which seem to do fine here, or do you have other solutions for us?

Answer: It would be helpful to see the insects up close to be sure of the problem. Please let me know if you can bring a sample of infested leaves to my office or if I may stop by your trees and see them in person.

One likely possibility is that sweet acacias (Vachellia farnesiana) are occasionally infested with insects called whiteflies. They are very small white insects in their adult form. As immature insects they are wingless, darker in color and suck sap from the leaves, sometimes causing the tree to drop leaves prematurely. Repeated infestations can be hard on the tree, but in many cases the infestation is not severe and natural enemies reduce the population to tolerable levels. In recent years these whiteflies seem to be more common in the Tucson area, probably due to warmer weather.

Whiteflies in general have been a sporadic problem at our elevation, whereas in lower and warmer areas such as Pinal and Maricopa counties, they are a regular occurrence. I would be interested to know which insecticide your landscaper is using. There might be other options for pest management. I wouldn’t recommend giving up on your trees yet.