Q: I keep seeing yellow wasps landing on the water in my swimming pool. What are they doing and should I be concerned?
A: The yellow wasps are likely paper wasps (Polistes flavus) and they are getting a drink of water. They are called paper wasps because they construct nests of paper from wood fibers they chew and mold into a nest shape. I would not be concerned. They are not aggressive unless you approach their nest. They are considered beneficial insects because they are predators of caterpillars and other insects.
Q: When and how do I plant garlic?
A: Garlic is best planted in October and early November. Individual cloves can be planted pointy side down in rich, well-drained soil about two inches deep. They need sun and water but not too much water or they will rot. When the tops dry down they are ready for harvest, most likely in May or early June.
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Q: I am wondering about adding some native grasses to our landscape. They are
1) Muhlenbergia dumosa, bamboo muhly;
2) Muhlenbergia rigens, deer grass; and
3) Stipa tenuissima, Mexican thread grass.
I know some grasses are invasive so I am concerned about them. Are there problems with them being invasive in other people’s yards or over populating?
A: Our friends at the Natural Resources Conservation Service are experts in this area and they say the Muhlenbergia species are native to Arizona and are commonly used in landscaping here. Bamboo muhly typically spreads very slowly by rhizomes and doesn’t readily re-seed. Deer grass also doesn’t really “move around” in the landscape. I wouldn’t suggest the use of Mexican feather/thread grass in landscapes as it does have the potential to become invasive.
Q: My pine tree appears to be dying from the top down. Is there anything I can do to help it survive?
A: The answer is maybe. There is a bark beetle that attacks pine trees and if your tree is infested that means trouble. Tell tale signs that you have these beetles include red sawdust at the base of the tree and round exit holes in the bark about the size of a pencil point.
The best defense against these beetles is keeping your tree healthy by giving it enough water to survive. The trees we have in the Tucson area at lower elevations are mostly Aleppo and Eldarica pines and they can get quite large. These trees require significant watering throughout the year, especially in the summer.
We recommend watering every one to two weeks in the summer and every two to three weeks in the winter. The water should be delivered to the absorbing root zone which begins near the edge of the crown of the tree and extends outward. Since the Aleppo pines can get very wide this is not a trivial task. Placing a hose at the trunk of the tree does very little good. The water should reach a depth of two to three feet and this can be measured with a soil probe.
Peter Warren is the urban horticulture agent for the Pima County Cooperative Extension at the University of Arizona. He works with landscape professionals, urban farmers and homeowners to promote integrated pest management and best management practices for desert horticulture in southern Arizona. Send questions to plwarren@cals.arizona.edu