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THE PROS AND CONS OF VARIOUS ORGANIC MULCHES

Gardeners who are into organic mulches should get hold of the July/August issue of Organic Gardening magazine. It explores the many types of mulches, from bark and wood chips to grass clippings to pine needles. Most of the information is based on research on the good and bad characteristics of each kind.

This column will explore some of the highlights.

On the whole, it appears that grass clippings outperformed most other choices, at least in the vegetable garden. This gardener is not sure that they fit the bill in ornamental beds of flowers or shrubs, simply because they don't have the looks of a good bark mulch.

Perhaps the greatest attribute of grass clippings is that as they break down, they provide some nutrients to the soil, namely nitrogen. At the end of the season, any remaining mulch can be turned into the soil.

Grass clippings should be dried before being used in the garden and piled three to four inches thick to last most of the season. Be sure the lawn has not been treated with herbicides in the past three mowings, and avoid any clippings that may contain weed and grass seeds or seed heads.

One other negative on grass clippings is that they do not last long and may need replenishing during the growing season.

Newspaper of two or more sheets or shredded also rated high in the ability to control weeds. Shredded papers should be piled high, up to six inches.

This one probably should be limited to the vegetable garden based on looks alone. I don't think I'd like to be reading snippets of the paper while looking over my perennials. Newspapers also breaks down rather quickly.

What the article did report, based on research based from the U.S. Department of Agriculture lab in Beltsville, Md., is that "there is nothing in black-and-white or color newsprint that will damage your plants or harm the soil." There is still a caution on the use of slick paper, but even the colored newsprint is apparently now OK.

The article also took a look at pine needles as mulch. This product is used much more down South than it is in Western New York. Yet it is an excellent mulch. I have gathered it myself from the forest floor of "piney woods" and found it to work very well.

Among the beliefs shattered is the notion that the needles will acidify the soil to a point where the plants won't perform. Studies have shown that after two years of mulching, the pH of the soil below varied little if any.

The challenge with pine needles in our area is finding them.

Straw is an old-time favorite. In addition to the other good things straw does (controls weeds and holds in moisture), it also helped with disease and insect control. Studies showed significantly less leaf diseases on tomatoes and fewer Colorado potato beetles on potatoes in plots mulched with straw.

Once again, straw is probably limited to vegetables because of its looks.

Last but certainly not least are the bark and wood chips that are very commonly sold in Western New York. Both ranked well in durability, though wood chips tend to break down faster.

Do not worry about starving soils of nitrogen with these mulches as long as they are left on top. Gardeners should always avoid mixing these materials, especially wood chips, into soils, as plants will not grow well in "woody" soils deprived of nitrogen.

Piled on at a thickness of 2 to 3 inches, they will hold significant amounts of moisture in the soil and control weeds adequately. They are best used in ornamental beds rather than vegetable gardens.

Organic mulches are not without their drawbacks -- they can create a home for mice and slugs. But in most cases, the benefits outweigh the liabilities.

What's the best mulch? I have always maintained, and still do, that the best mulch is what the individual gardener likes the looks of best. Availability and cost should play a role in the selection, but use mulches and your plants will love you for it.

Q -- The lower leaves on my foxglove have all dried up, and even the flowers are turning brown. I can't believe that it's been too dry. Any thoughts?

-- R.G., Tonawanda
A -- There are probably two possibilities. One is thrips, the other spider mites. I have seen a sample of a severe thrips infestation on foxglove this season, so my guess is that they are the culprits. You may want to take a sample to Cornell Cooperative Extension or a garden center for identification.

Cornell recommends malathion or diazinon for thrips control on onions, so I would explore using either of them first. Malathion is often recommended for spider mites as well. Check the product to be sure it is labeled for perennial flowers and that there are no precautions about spraying on foxglove.

All sprays should be applied to hit the bottom of the leaves and the flower stem. Flowers can be injured by pesticide sprays; expect some additional browning. When the plants appear to be lost, pull and or cut them to remove as much debris and insects from the garden as possible. Next year start sprays as soon as the damage first begins to appear.

Q -- I have a several varieties of hop plants. They are trained to crawl up a string trellis that I built. This year, however, they have turned brown starting at the bottom. There are skinny, chartreuse-colored insects about a quarter-inch long on the bottom of the leaves. The bugs move very quickly. Are they hurting my plants?

-- T.W., Tonawanda
A -- The insects sound like leafhoppers. They are common on a number of plants and trees. Usually they are not very damaging, but when present in high numbers on plants like potato, they can be troublesome.

The problem in this case is that hops are such an obscure plant that you will never find an insecticide labeled for application to them. Sevin is recommended for leafhoppers on potato. Check the label at a local garden center to see if one might have hops on it. Good luck with the brew.

For answers to your gardening questions, send a self-addressed, stamped envelope to Ken Brown, in care of the Features Department, Buffalo News, P.O. Box 100, Buffalo, N.Y. 14240. Brown is a horticultural consultant specializing in integrated pest management.

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