A few solutions to seasonal growing pains

July 15, 2011

Many of you have encountered problems during this year’s growing season. Here are some of the issues you’ve struggled with and my advice on how to deal with them:

I have two young (about 10 years old) kwanzan cherry trees, both of which have large gaps in their bark. Do you know what these gaps are? Can they kill the trees? Can I do anything to stop them?

Your trees could be suffering from a bacterial/fungal infection or their bark may have sustained damage. The bark of a young kwanzan cherry tree is thin, which makes it vulnerable to scrapes, especially when the tree is transported or planted. Lawn mowers and string trimmers also can injure the bark. The injury can develop into scars or gaps like the ones you describe, exposing the inside of the tree (or heartwood) to insect damage and rot.

The only thing you can do is protect the damaged area. If the exposed heartwood develops a soft, pithy feel, you should scrape it back to solid wood with a pruning knife. Continue to monitor. As long as the foliage is full and appears healthy, your trees might live to flower for many years.

The character that the wood develops as it ages is the beauty of these trees. Their thick stems, clubby appearance and pompom double-pink flowers make them easy to recognize among the flowering cherries that grow in the Washington region.

Wild strawberries are gradually taking over my lawn. I can’t find anything that will kill them without also killing the grass. So I’m reduced to using Roundup and then reseeding the dead area. Is there a better answer?

Unfortunately, there is no selective weed control in this case. You’ll have to stick with the Roundup or use white vinegar right off the grocery store shelf — an alternative approved by the Environmental Protection Agency. You should use a plastic sprayer with either one since both herbicides corrode metal.

If you get tired of battling the weeds, you could simply embrace them and nurture a strawberry patch. But beware, there are two lawn weeds that look like wild strawberries, but only one of them truly is. Fragaria virginiana is the real thing. It has white flowers and a compound leaf with three leaflets. Its fruits are as good as the cultivated varieties.

By contrast, cinquefoil (Potentilla norvegica) has yellow flowers and a compound leaf with five leaflets. The red fruits of cinquefoil can be eaten, but have little to no flavor.

For the second year in a row, my potted basil plants reached about 2 feet in height then turned mottled yellow, wilted and died. This has never happened before. Same pots, same potting soil. I have a new starter plant, but wanted your comments before transplanting it.

Your basil is most likely infected with a fungus (Fusarium oxysporum.) This is one of the most frequent diseases that basil contracts, but the symptoms only present themselves in common or sweet basil (Ocimum basilicum.)

There is no way of destroying the fungus once it has been introduced into the container or the soil in which the basil is planted. The fungus will persist at least four to eight years, so you should not plant your new starts in the same soil or containers used to grow the infected basil.

If you’re planting the starts in a garden, keep them far from the infected site. The fungus spreads by splashing from rain and over-watering. Also, keep the starts away from other plants in the mint family, which can carry the fungus but are not affected by the wilt.

There are sweet basil hybrids that are resistant to fusarium wilt. Look for them at your garden center or seed catalogues.

In a previous column, you advised against cutting back azaleas in May. If cutting back is necessary, what is the best time of year to do this? I like to let my azaleas grow naturally, but have to keep them in check so they don’t block the windows.

Azaleas should be pruned just as their flowers fade. The exact timing depends on what kind of azalea you have. But whenever you prune, you should do it selectively and shape the azaleas lightly to yield a shrub with a maximum number of spring flowers .

May is when azaleas generally start to form the flower buds that will open next spring. If you prune in May and destroy the buds, the shrub will be flowerless the following season, which is why I recommend against doing that. Prune just after they flower.

If your azalea shrub grows out of control, you can try “renewal pruning.” This method requires that you whack the shrub in half or to the ground — preferably in late February or early March, before growth begins. In this situation, you will sacrifice one year of flowers but the newly leafed plant will be low-growing, fuller and flower dependably in subsequent years. Renewal pruning is only done every five to 10 years or more depending on growing conditions.

Fertilize in March or April.

Joel M. Lerner is president of Environmental Design in Capitol View Park.

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