Volume 13, Issue 17 ~ April 27 - May 4, 2005
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Dr. Gouin's Bay Gardener

Lush Lawns Love Limestone

Bay soil is better suited for growing cranberries and blueberries than for grass

If you want a lush weed-free lawn next year, now is the time to take action. If you haven’t had your soil tested in the past five years, it is likely that you will have to lime your soil. Soil in the Bay area tends to be very acidic. When you apply lawn fertilizers on acid soils, the chances are great that much of the nutrients from the fertilizers will either be washed into the Bay or into the groundwater.

If you want your lawn to be dark green and dense, this is the time to apply limestone — not fertilizer.

Lawn grasses grow best on soils that are only moderately acid. It is not uncommon to find soils in the Bay area having a pH of 4.2 to 4.5. Since a pH of 7 is neutral, this means that such soils are very acid and would be ideal for growing cranberries and blueberries — if we had the proper climatic conditions.

By applying limestone now, you’ll neutralize your soil, bringing it closer to the ideal soil pH for growing lawns, between 6.0 and 6.5. At these pH’s, all of the nutrients essential for good plant growth are available to the roots of the grasses. In turn, fertilizers you may apply in fall — which is the best time to fertilize bluegrass and fescue lawns — will be effectively utilized by the lawn grasses.

Soil testing is the only sure way of determining the amount and kind of limestone to apply. If you don’t want to take the time to have your soil tested, then apply between 50 and 80 pounds of dolomitic limestone per 1,000 square feet. Do not use hydrated or high calcium limestone, since most of our soils are deficient in magnesium, and dolomitic limestone contains magnesium.

Now that you have limed your lawn, the next thing you will want to do is set your lawn mower as high as possible so as to cut the grass tall and let it fall, about which you’ll read more next week.

Q I’m told that azaleas need acidic soil. What can I use besides Miracid? I’d like an organic substitute. And is it true that nearby concrete isn’t good for azaleas?

—Marnie Morris, Rose Haven

A How do you know that your soil is not already acid? I have seen some soils that were so acid that the plants died. Often I recommend that azaleas be limed because the soils are too acidic. The ideal pH for azaleas and rhododendrons is 5.0. Many of the soils around the Bay are 4.2 to 4.5. Test your soil; then you can take the appropriate action.

Professor Emeritus Francis Gouin retired from the University of Maryland, where he was the state’s extension specialist in ornamental horticulture. Follow his column of practical gardening and plant advice every week, only in Bay Weekly. Ask Dr. Gouin your questions at [email protected].

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