Pruning oleander will eliminate flowers for a while

Q: My oleanders need trimming. They are still blooming and the weather is hot. Is it safe to trim them now or did I miss my opportunity?

A: You can trim oleander anytime but it makes flowers on its new growth, not older growth from previous years. Trimming or pruning now will eliminate flowers for a while, but more flowers will be produced when it grows back.

Pruning or trimming now will result in a green shrub without any flowers for a while. If you are OK with that, then go ahead and prune. You won’t hurt anything.

The more you remove, the longer it will take before it flowers anew. This advice is for oleanders only. Other plants may react differently and could result in severe damage by pruning in mid-summer. But not oleander.

Q: We have a saguaro about 10 years old. A couple of months ago it started leaning and now is in danger of falling over although it still looks good. We staked it but are not sure what to do. It is about 6½ feet from the pool, but there doesn’t seem to be any water near it.

A: The reason a saguaro is leaning is because the roots cannot support the top weight. If the spread of the roots is large enough, it will not lean. There can be a couple of reasons why this is happening.

If the plants are getting watered too often, then two things might happen. First, watering too often can cause root death and a loss of roots that anchor the plant. The plant can start to lean. If the soil is prepared well before planting, root death from watering too often is difficult.

Watering too often can cause very strong top growth. There is nothing wrong with strong top growth if the roots can spread far enough to support the weight of the top. If the roots are kept small and the top grows a lot, then the plant can lean or even topple over.

Roots can be kept small by watering close to the trunk. If the only water a saguaro can get is close to the trunk, then the roots will grow only there. Drip emitters that apply water only a foot from the trunk cause a very small root system to develop. Applying water frequently next to the trunk with a hose can cause the same problem.

It is best to water no more often than once every three weeks. Distribute the water over a wide area near the trunk. This can be done by growing other plants in the general vicinity so the saguaro can draw upon water from these plants as well. Apply a generous amount if watering only this often; 10 to 20 gallons should be enough.

Q: I would like to start a raised bed garden in my side yard which faces west. Right now there are groundcover rocks. Can I put my raised garden on top of these rocks or do I need to remove the rocks first? In some places, they are almost a foot deep.

A: Having large rocks and putting a raised bed on top of it should pose no real problems, but I do want to express some concerns about how to do it.

There are two ways. Put a weed barrier down first that will let air and water through to the layer below and keep it separate from the rocks; or don’t use one and let the soil from the raised bed begin to settle into the rocks. Either one will work.

Some people are adamant about the weed barrier. I am not. If the rocks are larger than 3/8 inch, the water should drain easily from the raised bed into the rock layer. It’s important that the raised bed drains easily.

Some will argue that having a raised bed over rock actually benefits drainage, similar to putting potting soil in a container with rocks at the bottom. This isn’t true. Placing rock in the bottom of a container to improve drainage is an old wives’ tale.

Soil placed in the raised bed without a weed barrier will sink for the first couple of months so be prepared to “top off” the raised bed later. The raised bed with the weed barrier is less likely to do that.

Soil in all raised beds will settle to some degree, but normal settling is about an inch. The raised bed over rock will probably sink much more than this, but it would be hard to estimate because it varies with the size of the spaces between the rocks.

To grow some decent root crops (I am thinking of some of the longer/larger carrots) you will need a 12-inch depth of soil that is free of large rocks. Raised beds filled with a manufactured soil mix (usually a mixture of compost and sand) will provide a rock-free soil.

Use a soil mix that has a good quality of sand mixed in it. I would rather see gardeners pay more upfront for a better soil mix at the start than buying the cheapest one they can find. Cheap soil mixes will use inferior sand. Soil mixes for raised beds are permanent. Once you commit to a soil mix, you are stuck with it. So get a good one right off the bat.

Q: I have 8-year-old palm trees in my backyard and this year they decided to flower and seed. This is the first year they have done this. Is this normal or is something else going on? They make a mess so is there anything I can do to stop or slow how much they produce? Is it okay to trim these flowering stems out? Can I do it before they flower?

A: Once palm trees reach maturity, they flower, fruit and produce seed. This is normal. They can be a big problem in landscapes because the seed they produce readily germinates in wet areas and produce seedlings. The germination percentage of palm seeds is near 100 percent.

When planted near pools, the seed is a bad litter problem at the bottom of pools for a few weeks during the year. They are small and don’t float so they are difficult to remove.

There is nothing you can do to stop them from flowering. Sprays that prevent flowering and fruiting in ornamental trees are not labeled for palms and probably will not work; palms are in a different plant category than most other ornamentals.

One solution is to prune out flower stems when you see them as you are suggesting. While you are at it, coordinate the pruning of the palm tree with flower removal and do it all at once. Removal of the flower stems makes no difference to the palm tree.

Q: Tons of little black and yellow striped beetles are hanging out on my tomatillo plants. What are they? What is the best way to deal with them?

A: From the photo you sent, it looks like the striped cucumber beetle. It gets its name because it is commonly found on cucumber but can feed on tomatillo as well. However, there are only a few reports of this bug as a problem on tomatillo.

It certainly is a problem on cucumber and others in the same family of vegetables as cucumber including melons and squash.

This may sound laborious but a cordless vacuum cleaner works well when removing these insects from plants without insecticides. Soap and water sprays also work, but they have to be done two or three times a week. Soap and water sprays kill all insects, even good ones, so be careful where soap and water sprays land. Soap and water sprays are insecticides.

The next step up in toxicity would be pyrethrin garden sprays. Pyrethrins should knock them down pretty well. Again, pyrethrin sprays are not selective so they will damage any insect that comes in contact with this insecticide.

After pyrethrins, you have some of the so-called “hard pesticides” such as Sevin, Malathion and other traditional garden insecticides. You can try planting a trap crop, a couple of plants that they like better, such as cucumbers or melons, and see if you can draw them off of your tomatillo using sacrificial cucumber or melon plants.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.