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Nematodes are manageable, but never go away


Q. Are these nematodes on my tomato roots in the picture I sent to you?

A. Yes, you have them. Once you have nematodes they are a permanent pest in your vegetable garden. Your future with them is in managing their new home but you will never be rid of them.

In the past, soil fumigants were available that would dramatically reduce their numbers and easily make them manageable. These soil fumigants are no longer available to homeowners and highly restricted even for commercial applicators because of their potential to harm the environment.

There are multiple approaches in managing nematodes. One way is to exclude them. You can do this by growing vegetables that are highly susceptible in pots or containers. If the pots or containers are in direct contact with the soil containing nematodes, the nematodes will move into the container eventually.

You can impede this by putting a layer of coarse gravel on top of the soil and putting the containers on top of the gravel.

If you want to grow in the ground with nematodes, then heavily enriching the soil with organic material such as high-quality compost will help deter them. Keeping the soil as healthy as possible is a great deterrent. Nematodes do not seem to like heavily enriched soils.

Another deterrent is to select plants that nematodes don’t seem to like very much. There are some vegetables somewhat resistant to nematodes but it is quite lengthy. I will post this list on my blog but a few of them include broccoli, cauliflower, chives and many mustards.

There are other plants that nematodes really like a lot but plant breeding has produced some varieties that are resistant to nematodes and a few plant diseases. These varieties have capital letters such as V, F, T, N after their names that designate their resistance. The capital N in this case designates nematodes.

Another method is growing marigolds in the vegetable plot. The most effective way is to grow a solid stand of marigolds for at least two to three months in the planting bed. Turn these marigolds under the soil so that they decompose. Then plant your vegetables.

Some people grow them on the borders of the vegetable plot but it is not as effective as growing a solid stand and turning them under.

There are some products available, such as Clandosan, which give some benefit and could also be incorporated into the soil.

Q. We winter in Boulder City in a condo RV park. Three years ago we planted a rose bush that did wonderfully well until it died over the summer. The pot gets plenty of water from a drip hose. We’d like to put something in the pot more capable of surviving the extremes of the high desert. I would be happy with anything that will flower or fruit when we are here in the winter and is OK with being abandoned for six months.

A. It will be very difficult to grow much of anything in a pot if it is not attended to. You might be better off putting something there that will not die and while you are here growing something that you can dispose of when you leave, such as an annual.

The other possibility is to have someone care for your plants while you are gone. The summers here are brutal on plants as you know. We get fluctuations in our weather that are very unpredictable.

If you insist on growing something in a container, then double pot your container so that the container you are growing in is surrounded by another container or object that shades the outside of the inner container.

Surface temperatures of containers that receive direct sunlight in late spring and summer will produce temperatures inside the container that will kill plant roots. Double potting a container with a larger container with gravel in the bottom and just air space on the sides will help insulate the soil inside the container.

Surface temperatures of a container will easily rise above 165 degrees Fahrenheit in direct sunlight. This heat transfers to the soil and cooks the roots on the side exposed.

Another possibility will be to grow cactuses in containers and watering it no more than about once every two weeks. Once a week, if the container is small. Make sure the soil for the cactus drains readily. The container should still be double potted.

Q. Should a newly planted 36-inch boxed purple robe tree have its nursery stake removed? I sent you a picture of it.

A. Larger trees need their roots stabilized for one to two growing seasons and then the stakes removed. In your case, the tree has poor trunk strength since the trunk has no taper to it and the trunk will snap in high winds.

Immobilize the roots by restaking the tree. Let side branches develop along the trunk to improve trunk taper and strengthen it. Normally, a tree with good trunk taper can have its stakes removed after one to two growing seasons. A tree with poor trunk taper will require a longer staking time to strengthen the trunk and give it solid rooting into the surrounding soil.

Allowing side branches to grow along the trunk helps promote tapering in the trunk reducing its need for staking after one season.

Ideally, the tree should have small stems growing from the trunk covered in leaves, removing them only when they reach about pencil diameter. This increases stem taper, reduces the possibility of shear or snapping in high winds.

Trees also need to “sway” in the wind. This swaying or movement of the trunk from side to side also helps to develop taper in the trunk. But the roots of the tree need to hold the trunk in place at the bottom.

This tree will need to be staked for a while to keep the trunk from snapping. Probably at least one season. I would probably restake the tree with either two or three stakes to support the trunk and keep it from bending to the point where it could snap and immobilize the roots.

Two methods used for restaking include a two- to three-stake method with the stakes driven into the solid soil beneath the root ball. The other way is to use guy wires to stabilize the tree. I supplied pictures that I will also post on my blog.

This next year let small branches grow from the trunk if they develop. These will increase the strength of the trunk and help reduce sun damage to it as well.

Remove older branches from the trunk when they get larger than a pencil in diameter. Cut them off flush with the trunk. Do not use pruning paint.

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.