Here is a topic I want to revisit, since some good information has come to my attention: What is a good choice for an evergreen screen in the Napa area?

I’ve written about the Leyland cypress problem before. That tree has the shape, color and size, but it just doesn’t last in the Napa area because it is terribly susceptible to cypress canker, a fungal disease. Ample irrigation might help, but it doesn’t solve the problem.

I recently found out about a good potential  alternative: Thuja ‘Green Giant.’ It is a hybrid of western red cedar (Thuja plicata) and T. standishii, (Japanes arborvitae). Someone I know planted a row of them here in the Napa area in the last year, and it got my attention. Not having seen it before, I checked around online and found some encouraging information.

Then, coincidentally, on a recent trip to Bartlett Tree Experts Tree Research Laboratories and Arboretum in Charlotte, N.C., I saw a beautiful row of ‘Green Giants’ in the Arboretum. They are tall, rich, green, slender pyramids, very similar to Leyland cypress in color, texture and structure. These specimens are about          25 feet tall and may eventually grow to about 60 feet, unless they are pruned on a regular basis to keep them smaller. That size, shape and color category is difficult to fill in our region. 

The arboretum also had some Leyland cypresses, which looked healthy, too. However, the tree researcher leading our tour took time to discuss the cypress canker problem. Even with the North Carolina humidity and summer rainfall, cypress canker is a problem there too, albeit not as severe.

‘Green Giant’ will need long-term irrigation in the landscape, but it appears to be a very promising tree for the Napa region, without the cypress canker problem.

An online search turned up a growers own glowing review. I’m skeptical of product reviews written by the producer, so I dug a little and found one by the U.S. National Arboretum (USDA Research Service). It says the tree is “adaptable … tolerates a wide range of soil and hardiness zones and is not troubled by significant pest or disease problems” and calls it a “suitable alternative to Leyland cypress.”

So, with respect to my recent columns on the subject of tree selection and giving trees the space they need, for heaven’s sake, do not plant Leyland cypress around here, and think twice before planting coast redwoods where space is limited.

Consider Thuja ‘Green Giant’ for a cool green screen.

Here’s a good question that came up recently:

“My crape myrtle tree was planted two years ago and bloomed the first year. It is approximately   8 feet tall. It did not bloom last year or this year. The leaves are bronze-edged. The tree gets good sun and water. We have the usual clay soil. Do I need to fertilize or do something else to make it bloom? I noticed the crape myrtle street trees in my neighborhood, which are older, have started blooming.” - LM

Dear LM: I have seen this happen. As a matter of fact, it is happening with my own crape myrtle in my back yard, growing in compacted soil.

Crape myrtles bloom on new shoots that emerge each year. This year’s new growth produces flowers at the tips. If the tree does not grow vigorously, it might not bloom. That appears to be the case with my own tree.

The bronzy color of the leaves is indicative of stress and mineral deficiencies, which may result from the irrigation not actually penetrating the root zone. Combined with tight clay soil this inhibits growth.

I gave my crape myrtle a couple of drenches with liquid fertilizer this summer. The foliar color improved from bronze to bronzy green, but the tree did not bloom. I didn’t really expect it to respond dramatically to a couple shots of fertilizer. 

A better approach would be to loosen the soil in the tree root zone to allow for improved root growth. And that’s what I’m going to do this winter.

Again, coincidentally, this  was demonstrated at the Bartlett Arboretum, for a crape myrtle showing unsatisfactory growth. They showed how compacted soil can be cultivated and amended using an Air Spade — a high-pressure pneumatic tool — that can dig trenches and loosen soil without damaging pipes, wires or roots.

As they demonstrated, the root zone is thoroughly moistened and dressed with compost and any particular minerals supplements that lab analysis finds to be lacking. Then, the Air Spade is used to loosen the soil and incorporate the compost to a depth of about 6 inches. 

Do-it-yourself gardeners could accomplish similar results using a spading fork, with less expense, harder labor, and greater potential for damaging the roots in the process.

There are other possible reasons why a crape myrtle might fail to thrive, but a good place to start working on is soil texture, structure, fertility and moisture content.

Bill Pramuk is a registered consulting arborist. Visit his Web site, www.billpramuk.com, e-mail questions to info@billpramuk.com, or call him at 226-2884.