'A' as in Aging Gracefully

Q We inherited an apple tree eight years ago that is quite old -- the house dates to the 1960s. The flowering and vigor have diminished with each year. We have pruned it, but it is now very vertical and about 20 feet high. Should we top it? Is there anything else we can do, or should we take it down?

A Apples are some of the longest-lived fruit trees, and can bear good crops for decades if pruned correctly and sprayed for pests and diseases at critical points in the growing year.

Pruning is aimed at producing an architecture that, ideally, consists of a strong central leader and roughly horizontal scaffold branches that bear fruit. For ease of harvest, trees often are allowed to branch close to the ground and their height kept to about 20 feet. You should head the tree back to this level and thin the branch structure to a total of no more than 10 main branches. If key branches are growing upright, you can encourage flower and fruit production by forcing them to grow more horizontally, using spreaders of wood or plastic to force more lateral growth. This is best done, of course, when the tree is young and the branches are supple, but the technique can be effective on older branches. Through the miracle of plant hormones, horizontal branches flower and fruit much more freely than vertical branches.

If you don't care to harvest any fruit but want to keep the trees for their spring flowers alone, you can prune them a bit less, focusing on removing any crossing or wounded branches and any branches that are growing inward toward the center of the tree.

If you want to harvest fruit, you should apply an orchard spray containing a fungicide and an insecticide. Do so at least twice in the spring, once when the flower buds begin to show color and are on the verge of opening, and again when the petals are falling. This should take care of the plum curculio, a ubiquitous pest of fruit trees that will scar and deform your fruit if left unchecked, as well as fungal diseases such as scab.

Follow-up sprays may be of some benefit for some diseases and pests, but the first two are critical to success.

I lost seven of 13 Leyland cypresses planted as a screen because of a heavy snowfall last winter. They were in a somewhat shaded area and were growing to 25 feet. Can you recommend some replacements?

I recommend the arborvitae variety Green Giant. I worry that Green Giant is being over-planted, as the Leyland cypress has been, but it has much more going for it. It has an odd and highly desirable trait of growing quickly but then slowing as it matures. The cypress, by contrast, is a vigorous hybrid that doesn't know when to stop.

The arborvitae should grow quickly to reestablish the screen. Green Giant also fared much better than Leyland cypress in that heavy snowfall because its branches are naturally more horizontal and thus stronger. It grows to about 25 feet high and 10 feet wide, a size that is better suited to screen plantings than the much larger Leyland cypress.

I have a honeylocust tree with a great number of surface roots showing. I don't know whether to lay mulch over them or to add topsoil and plant some form of ground cover. Do you think either approach would harm the tree?

You can still mulch your honeylocust, but there is no need to bury the roots in it. Trees naturally develop surface roots, particularly in heavy soils. The roots are near the surface because that is where the oxygen is. If you bury them in a deep layer of mulch, you may decrease the oxygen available to the roots, and rainfall may even sheet off the mulch if it is laid in a thick layer.

Similarly, adding topsoil will bury the roots, which are now positioned optimally for the soil they are growing in, and I would not recommend taking this approach.

A ground cover should not harm the tree, but there is no obligation to plant it. The base of a tree can look perfectly dressed with a thin layer of mulch in the areas between the exposed roots. Pull any weeds that may appear.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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