Cool temperatures will damage oleanders

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For more information and directions, call the master gardener help line at 257-5555.

Q: I have several dwarf oleanders where the leaves have turned hard and brittle after this winter. I think this is the result of the hard freeze around New Year’s. The branches are still flexible and seem to be OK. Will the leaves fall off and be replaced? Is there anything I should do to keep them healthy?

A: Dwarf oleanders are more tender than the standard oleander and can be hurt at around 26 F; if it gets much lower than this, you might lose the entire plant. At least this is my experience with the dwarf type that has salmon-colored flowers. There is a fairly wide variation in cold tolerance even among the standard oleanders.

There’s not much you can do. Leaves are the first thing to get damaged. As temperatures drop more or for longer periods of time, then we see branch dieback.

Wait and see how they recover. Prune after you see where new growth comes from.

Q: We have some cherry laurel trees that are about 8 years old. The last couple of years we have had a struggle trying to keep them alive or even looking good. Can you give us some advise on what to do?

A: This is not a terribly good plant for this climate. Usually around year five after planting they start to decline, especially if they are planted in the wrong location or rock mulch is used around the base of them. These are not desert-adapted trees and they do not like soils coming from arid or desert parts of the world.

First of all, they need to be in the right location. They will do poorly if they receive late afternoon sun during the hot times of the year. They do not like to be planted close to walls that face west or south. They should be located, if planted at all, on the east or north sides of buildings where they can be shaded in the afternoons.

They will frequently do OK if they are planted with lots of organic matter in the planting hole. They should be heavily mulched as well.

The soils around them need to be modified with compost or decaying organic material to keep them happy. Rock mulches allow organic material in the soil to slowly disappear in about three to five years leaving the soil void of the types of things they prefer. As they approach the three-to-five-year mark, their canopies begin to thin, leaves began to drop, and existing leaves burn around the edges or scorch.

These are sure signs they are not planted in the right spot and are not given the right amendments . If it is planted in the wrong microclimate of the yard, there’s not anything you can do but remove it since relocating it will be nearly impossible or impractical. If it is in a good spot in the yard, you might try adding compost around the base of the tree and organic wood mulch so it will begin to decompose back into the soil.

Remember to water the plant deeply and not let the soil go dry between irrigations. On the other hand, if you keep it constantly wet or too wet, you’ll probably kill it due to root rots.

Q: Last year you gave me the name of a chemical spray that I could use on a nectarine tree that had thrips’ damage to the fruit. I cannot remember the name of the spray and would like you to send me this information, also when to apply it. Can this spray be purchased at any nursery? In saying the above. I did bring the fruit to you and this was the diagnosis.

A: The spray is spinosad. It may not be the trade name but will be in the ingredients. Make sure the spray is for fruit trees. Spray about every seven days.

I like to rotate it with soap-and-water sprays so that one week I use spinosad and the next I use soap and water. Cover the fruit thoroughly and start immediately after the petals fall from the flowers and fruit is forming.

Q: Can I use dried pine needles as mulch for my trees and plants? I have several fruit and nut trees as well as oak, Australian bottle, magnolia, grapes and several others. If it is good mulch, what types of trees should I avoid using the mulch on?

A: It is always best to have a variety of green waste as mulch rather than focus on one type, but there is nothing wrong with pine needles as mulch. There was a rather prestigious golf course in town that spent a considerable amount of money hauling in pine needles from North Carolina for mulch.

I would not be afraid to use it . Most plants will benefit from organic mulches. It is just that some plants, such as desert trees and shrubs, can handle growing in soils with very low organic matter better than nondesert types. It does not mean that they can’t grow in a better soil, it is just that they are better at tolerating poorer types of soils.

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 morrisr@unce.unr.edu.