Topic of companion planting controversial

A: This plant can be grown as a shrub or small tree. As a shrub, let it continue to grow as it is except for any weak stems. Any weak, floppy stems should be cut back about one-third to half their length to encourage them to become stronger.

As a tree, it can be grown with a single trunk or multiple trunks. This initial pruning should be done during the winter or early spring to establish its architecture or form. It is not too late now.

If you plan to use this as a small tree, I would select three or five larger-diameter stems (an odd number is more pleasing to the eye) coming from the ground and eliminate all other growth coming from the base. As new growth appears from the base, eliminate it at any time of the year you see it.

Next, stake these stems individually in an arrangement you would like them to grow. Staking young stems for one year will encourage them to continue growing in those directions.

Finally, cut any long, floppy stems back to encourage strength. Make these cuts ¼ inch above a side branch in any direction away from the wall. Remove any strong growth growing toward the wall.

Q: I am looking for a spring companion list for Las Vegas. I have an easy-to-read chart for fall that shows where to put different plants and which ones don’t like to be next to one another. I can’t find the same resource for spring.

A: The topic of companion planting is very large and has a lot of good information. But, unfortunately, it also has a lot of folklore that is either regional or lacks validation.

Companion planting can focus on the interplanting of crops, the use of understory crops, the planting of trap crops, suppression of pests by other plants, planting to increase the levels of predators and more.

For the general public, the term has evolved into the planting of crops for mutual benefit. Without getting into much detail, companion plants are sometimes referred to as “friends” to other plants.

There is good evidence for the planting of trap crops for aphids, whiteflies, nematodes and a few other pests. I have heard anecdotal evidence for the use of plants like garlic for repelling certain types of insects or even rabbits. Some people will swear by it and other people who have tried it may say it doesn’t work.

This opens another set of problems because in some cases it may work and in other cases it may not, which causes further confusion. I have tried to maintain neutrality on these issues and recommend situations where I am comfortable there is solid scientific research to support it or not support it.

I am comfortable recommending companion plants in the areas of trap cropping, intercropping and the planting of understory plants. There is solid evidence that interplanting of crops can provide some big benefits including a reduction of pest problems compared with large-scale monoculture in which only one crop is grown.

Without getting into detail, there are areas I am very uncomfortable making recommendations because there is contradictory information or the research flatly does not support it.

For people like yourself who want to experiment in these areas, I strongly support it and recommend that you test it for yourself. No one can dispute it if it works for you.

Some publications, such as Mother Earth News and the Old Farmer’s Almanac, support this kind of gardening. I have posted some other resources on my blog.

Q: I have a garden train in my yard and have dwarf Yaupon holly trained to look like small trees. Should they be left in the pots they are growing in to keep them small or should they be planted directly in the ground without pots?

A: It sounds as if you want to keep these plants from getting larger. If so, the shortest answer is to keep them in containers or pots.

Restricting root growth (forcing them to become bound up in a container) helps control plant size. Other ways to aid in the manipulation of their size include the careful application of nitrogen fertilizers and water.

If these plants are in containers and planted in the ground, I’d recommend you plant them in double containers or double pots.

Double-potting means that one container is inserted into a second container that is buried into the ground close to its full height. There should be a layer of pea gravel in the bottom of the buried container to prevent the two from lodging.

During the growing season, the second pot should be lifted from the buried pot or twisted a half turn to prevent roots from entering the buried pot and eventually the soil. You would do this monthly. If roots from the second pot enter the soil, the plant will begin to grow as if it were planted in soil.

Once planted in the ground, the size of these plants will be harder to control. This is because their roots will be allowed to grow anywhere they prefer to grow with no boundaries except their genetics.

Many of the same principles used to control plant size in containers can also be used to control their size after planting in soil. But I emphasize that controlling their size will be harder once they are planted in the ground.

Once in the ground, size can be controlled by root pruning, top pruning, directing growth, applying smaller amounts of fertilizer (in particular nitrogen) and managing their water supply closely.

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.