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Dolomite, the wonder drug for Florida gardens

Published Apr. 8, 2000|Updated Sep. 27, 2005

Have you ever dashed to your favorite nursery, consumed by spring fever, plunked down some serious, hard-earned cash and returned home with armloads of flowering perennials or roses or flats of colorful annuals? Did you harbor optimistic visions of your landscape soon made lush and cheery and fragrant, the envy of the neighbors?

I'm willing to bet you lovingly planted them in holes improved with compost or peat, then faithfully fed them with miraculous soluble blue fertilizer. When they started to look sickly, rather than use pesticides, you may have tried the almost edible sounding elixirs of that perky guy on PBS and ended up with half the contents of your fridge and cupboards sprayed on the garden. Did you then resort to toxic pesticides? Did you in desperation give your plant pals pep talks, having heard they like being spoken to? Despite all this, did you end up once again with pathetic brown sticks in a garden as cheery as the Serbian countryside in February?

You are not alone. Many gardeners in Central Florida have concluded either that they have brown thumbs or that gardening here is impossible _ too many bugs and fungi. Now you know why so many yards here are brimming with plastic flowers!

What gives?

Your success is determined by what you give your sand. (Northern folks have soil.) Let's face it: We try to grow things in sand that is devoid of nutrients and organic matter and is highly acidic. Only coastal folks who notice abundant bits of seashells in their sand are spared this chronic problem that most of us face but don't know about.

Seashells are made of the same calcium carbonate in Tums antacids. An old Florida gardener's trick is to bury several handfuls of broken seashells or even broken chunks of cinder block (concrete also is calcium carbonate) beneath roses and hibiscus so that their roots will find some calcium slowly leaching out. You can fertilize and spray all you want, but if you don't annually "sweeten" your soil by neutralizing that acid with some form of calcium you will continue to feel like the Saddam Hussein of gardening. Why?

Excessively acid soil lacks the calcium that plants need as much as we do. It chemically "locks up" nutrients so the roots can't absorb them, and it fosters the growth of acid-loving weeds and harmful fungi and bacteria.

St. Augustine and Bermuda lawns are not only stunted by acid soil, they are constantly invaded by Florida's native acid-loving weeds, such as dollar weed and oxalis. Most fertilizers contain little or no calcium, and weed killers and fungal sprays suppress only symptoms. But you can cure the problem inexpensively and safely.

Take the money you were grudgingly paying a mediocre chemical lawn service and go to a garden center and buy a few hundred (yes, hundred) pounds of all-natural dolomitic limestone, also called dolomite. Just $3.50 for a 50-pound bag buys you the secret to the healthiest lawns and veggies and roses and citrus and perennials.

I literally cannot garden well in the Tampa Bay area without it and have depended on it since 1976 in my own gardens and those of my clients. Dolomite is a non-burning source of that all-important calcium that neutralizes acid, plus the essential mineral magnesium that our sand lacks. Plants use magnesium with iron to make their green chlorophyll. You may hear your lawn and gardens sigh with relief as you spread the dolomite all over by hand or with a spreader, about as heavily as a generous serving of Parmesan cheese on spaghetti. (Go heavy; it can't burn plants or lawns).

Dolomite also helps the summer rains leach toxic chemicals out of your soil. Sprinkle some in your containerized plants, too; most potting soil has very little calcium in it.

As your waterings and the rains and the earthworms slowly work this powdered rock mined in Crystal River into your soil, you will see the dramatic improvement in the color and growth you've always dreamed of.

How much to buy? A 50- by 50-foot lawn that has never been "sweetened" would readily gobble up four or five 50-pound bags. One hundred pounds yearly will keep the soil sweet and supplied with calcium and magnesium.

Dolomite once was hard to find, but it is showing up in most of the large garden centers as word of mouth spreads the good news of its effectiveness as an organic soil healer. While it helps you get good results with chemical fertilizers that provide the other main nutrients, it works even better with the cheaper organics you can buy at feed stores that I'll cover in future articles.

A few plants don't like anything more than a very light dusting of dolomite, as they want somewhat acid soil and yet need some calcium. The common ones we grow are ixora, azaleas, gardenias, potatoes and Bahia lawns, which tend to be weedy because that grass and the weeds both crave acid soil.

Feel better now? Let go of your gardener's guilt, and go tell your plants one last thing: "I am bringing home for you a bunch of dolomite!"

John Starnes is an avid gardener and landscape designer who studies, collects, cultivates and hybridizes roses for the diverse regions of Florida and Colorado. E-mail him at


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