Volume 16, Issue 30 - July 24 - July 30, 2008



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The Bay Gardener by Dr. Frank Gouin


Good Lawns Grow by Science,
not by Guesswork

Start with a soil test so you’ll know what you’re doing

My friend had his soil tested, as I preach in this column. So, based on soil test results, I calculated how much lime he needed to improve his lawn.

We add limestone to the soil to make the soil less acidic by raising the pH — and not just any limestone. Since most of our soils in Maryland are low to deficient in magnesium, choose dolomitic limestone. Dolomitic limestone is the only liming material that contains medium to high levels of magnesium as well as calcium. High-calcium limestone contains little to no magnesium.

Magnesium supports good plant growth by helping in the formation of chlorophyll. Plants growing in soils deficient in magnesium appear yellow-green and do not perform well. Since magnesium is not included in most fertilizers, the only sources for it are dolomitic limestone, Epsom salts and magnesium oxide.

Dolomitic limestone is truly the only dependable, long-lasting source for magnesium. Both Epsom salts and magnesium oxide only provide temporary relief and are used mostly to overcome an immediate deficiency.

I recommended that my friend apply 60 pounds of agricultural-grade dolomitic limestone for each 1,000 square feet.

Agricultural-grade means that calcium and/or magnesium contained in the limes are in about equal amounts of both oxide form and in carbonate form.

High carbonate means that the lime will persist longer in the soil; on the down side, you’ll have to use a greater amount to raise the pH or make the soil less acid.

High oxides mean that the lime will not persist as long in the soil; on the up side, you’ll need less to raise the pH. If you are going to be living on the property for more than one year, choose the highest amount of carbonates available.

There’s another way you can get fooled in buying agricultural grade lime, for it comes in two varieties, high calcium or dolomitic.

Buy dolomitic, I told my friend, because the magnesium level in his soil was low to medium.

He took my recommendation to a local agricultural supply dealer who tried to sell him a high-calcium limestone, telling him that it was the same as dolomitic limestone. After reading the list of ingredients on the bag, he argued that it was not dolomitic limestone, but they assured him it was. Fortunately, he stuck to his guns as they did not know what they were selling.

Have your soil tested by a reputable soil testing laboratory at least every three years. I use A&L Eastern Agrucultural Lab Inc, 7621 Whitepine Rd., Richmond, Virginia, 23237.

Ask Dr. Gouin your questions at frgouin@erols.com. All questions will appear in Bay Weekly. Please include your name and address.

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