Magical flower show nothing to keep mum about

Recently someone asked me if we still had mulch available at the Orchard in North Las Vegas. The answer is yes. The mulch is no longer outside the fence because of people dumping trash — even a sofa — at the mulch pile. So, we had to move it inside the fenced area. Mulch is available Tuesday and Saturday mornings from about 9 to 11. We can even help you load it. For directions to the Orchard, call our Master Gardener help line at 257-5555.

Q: I have an African sumac that is losing its leaves at an alarming rate. It’s about 4 years old and is around 15 feet tall. It has been healthy up until now, but I can see right through it and recently it looks sick. I have been hand-watering it along with the usual drip it’s been getting through these years. It is in full sun but has been thriving in that spot. There are no roots above ground. Do you have any ideas about how to save it?

A: Actually yours is about the fourth question about a sumac losing its leaves that I have had in the past month. With each one, I have to go back to the usual reasons for leaf drop since I really don’t have much more to go on.

Let me list the reasons for leaf drop without saying which is most likely. These are watering too frequently and applying too much water; watering too frequently but not applying enough water; applying enough water but not often enough; poor drainage and roots rotting; insects such as scale on limbs; diseases in limbs or trunk that plug the transport of water to the leaves; and drift of weed killers from your yard or a neighbor’s.

If the leaf drop is not sudden and massive, then we can usually rule out poor drainage, diseases of the limbs or trunk, and drift of weed killers. If the leaf drop is slow and progressive, then it is usually stress related from heat and water or natural leaf drop.

If the leaf drop is older leaves while the newer leaves do not drop, then it could be natural. Evergreens, like African sumac, have natural leaf drop around this time of year; so if it is not excessive, it is possible it could be natural.

If it is natural, then these will be the older leaves toward the inside of the tree. If it is not natural, then it is usually tied to watering and the heat. If it is watering, then you will have to find a happy balance between enough water and not enough.

Watering should be deep and not daily unless you have very, very sandy or gravelly soil and the soil can’t hold much water. You would know this because of the other plants in the landscape: They would need frequent watering as well.

When watering, you will need to put down a lot of water, probably somewhere around 30 to 40 gallons every time you water. In most cases it probably does not need water applied more than twice a week at this time of year. After watering this amount of water, it is important to give the soil a chance to drain around deep-rooted plants like trees and shrubs.

If this tree is on drip irrigation, then you would need several drip emitters, probably at least eight distributed under the canopy. These could also be watering other plants under the tree but you will need to increase the irrigation amount if there are other plants there.

If there are other plants beneath the tree, hopefully they are deep rooted as well. It would not be wise to have plants under the tree that require daily or twice-a-day waterings.

Q: Recently, because of some suggestions, I had the acidity in the soil adjusted and trees sprayed for borers to salvage my dying cypress trees. I was told it will take six months for the trees to recover and if not, I should respray them. Do you have any recommendations for me regarding my dying plants because I am running out remedies?

A: The soil acidity adjustment is not needed. Italian and Arizona cypress can handle high pH soils fine. I have never seen borers in Italian cypress, but Arizona cypresses do get borers frequently and it is a big problem.

If they are Italian cypress trees, the usual reason for problems is too frequent applications of water and mites, which can cause a dull, dusty look on the foliage, needle drop and browning. If there are borers in the Italian cypress, all you can do is what you are doing and have a professional apply the appropriate chemicals to try to get the problem under control.

If these are Arizona cypress trees and you see dieback in them, the damage has been done. Unfortunately, these trees are prone to severe borer attacks and I would not recommend planting them. The same is true for Hollywood twisted junipers.

Q: I would appreciate any tips to grow hibiscus plants. I bought two 5-gallon plants, a White Wings and a Lipstick. I have them where they get morning sun and afternoon shade. I would like to know how much to water and what to feed, and when.

A: Although they are two very different types of hibiscus, both are considered tropical so they run a good chance of freezing to the ground this winter. On nights when freezing temperatures approach, you will need to try to protect them. You will need to provide a protected area in the landscape, not just an eastern exposure.

Ideally, this would be on the east-facing side of the home with plenty of filtered light so they will continue to bloom, as well as get some protection from winds. They will need lots of morning sun or they will not continue to bloom. They need lots of compost when planting and will not do very well in a rock landscape, if that’s where they are, over time.

When young, I would give them about 5 gallons of water each time I watered. As they get older, you will need to increase the amount of water but keep the frequency the same once you find the right one. When getting it established, a hibiscus needs daily watering. Make sure the soil drains easily.

When blooming, fertilize them lightly once a month. Apply iron and a complete fertilizer high in phosphorus to the soil some time in February. Compost or any organic source of nutrients will really help this plant.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at extremehort@aol.com.