Richard Nunnally’s gardening column

Q:I have about 75 oak trees on my 3 acres of yard. I recently noticed that all the leaves on four trees in the same general area have died. Are the trees dead? What might have caused this? They appeared to be fine this spring.

Answer: Without seeing them, I can only make some guesses as to what may have happened. First, I would want to know the age of your house and whether any construction has been done in the area in the past couple of years. Has anything been done that may have changed the trees' environment or impacted their roots?

Trees store up food in the fall to make their leaves in the spring. Once they make their leaves, they have to rely on their root system to provide moisture and nutrients to sustain those leaves. If the roots have been disturbed or something has happened to prevent movement of water and nutrients up and down the trunk, the leaves and branches will die.

There are also insects called borers that infest trees near the ground. As they feed on the cambium around the circumference of the trunk, they cut off the food supply to the top. Consequently, the leaves die.

As you can see, there are several possibilities, but a site visit -- the sooner the better -- is the only way to determine the cause. My suggestion would be to have a certified arborist examine the trees. Since they looked fine a few months ago, I'm convinced that something has drastically impacted the root system.

However, if you wait a couple more months, it might be too late to make a good diagnosis.

Q:I have fertilized all my evergreen plants -- nandina, boxwood, camellias, etc. Should they be fertilized again in the summer, or should I wait until fall?

Answer: My recommendation is to feed most landscape plants only once a year. My experience has been that most evergreens grow faster than you'd like. Consequently, you find yourself having to prune them to keep them in scale with the landscape.

As for a schedule, nonblooming evergreens, such as boxwood, can be fertilized in early March before they start to produce new growth. Most blooming evergreens should be fertilized immediately after they finish blooming. The exception would be plants that are recently planted or have been through some extreme stress, such as disease, drought or winter injury.

I'm not a big fan of fall fertilization of evergreens, unless it is done after the first killing frost. Early fall fertilization can cause a late flush of growth if we have a mild fall. However, root feeding after the first good frost ensures that the fertilizer will be picked up by the roots of the plant and stored for use the next spring.

Q:Slugs have taken over my flower garden. They are having a feast on my hostas. What can I do?

Answer: Many gardeners use beer to control slugs. Simply sink a couple of empty butter tubs in the ground, like a small pool, with the lip of the tubs even with the ground. Sometime after dinner fill them with beer. Slugs are attracted to the odor and they crawl in and drown.

It usually takes a day or two for the slugs to find the beer, but once they do, you'll find lots of them in each tub in the morning. When your tubs show up empty for a few days, you can stop putting out the beer. As strange as this may sound, it works and it doesn't hurt anything else.

Richard Nunnally is a freelance writer and host of WCVE's monthly gardening show, "Virginia Home Grown." He can be contacted at .