The Challenge of Sandy Soil

by Dotti Hydue

Gardeners know how important good soil is for healthy, productive plants. The ideal soil is loam, a mixture of sand, silt, clay and organic matter. But loam is hard to come by in Florida.

From the Keys to the Panhandle, from the Atlantic coast to the Gulf of Mexico, Florida is awash in sand: mucky sand, coarse sand, sugar sand — you get the idea. In fact, our official state soil is a type of sand unique to Florida called Myakka, a fine, light gray sand that covers more than 1.5 million acres of the state. Formed in sandy marine deposits, Myakka soils are the most prevalent soil types in the state — if you can call them “soil.”

One benefit to gardening in sand is the ease with which it can be worked. Root vegetables and cash crops of peanuts, cucumbers and watermelons thrive in loose, sandy ground. And the irregularly-shaped sand particles allow for easier air circulation and fast drainage, so there is less chance of losing plants to root rot due to heavy, soggy soil.

But these qualities are also drawbacks. The surface of dry sand tends to repel water. Repeated soakings will
eventually penetrate that barrier and allow water to flow deeper into the ground. And flow it does. With no organic matter to hold the water, it quickly flushes through the sand, taking with it any soluble nutrients that might be present. Beneficial fungi and bacteria that break down organic matter and inhibit harmful organisms, such as plant-parasitic nematodes, don’t work as effectively in sand.

What can we do? Amend, amend, amend. We need to add something to our sandbox that will hold both water and nutrients and create a suitable environment for beneficial soil organisms. That “something” is organic matter. Because amending garden soil is an ongoing process, amendments should be reasonably priced and easy to obtain and incorporate. Some of the more-readily available forms of organic matter are peat moss, compost, animal manures, green manures and leaves.

Brown-colored peat moss consists of compacted deposits of partially decomposed organic
debris created under relatively airless conditions. It takes hundreds of years to form. Peat moss binds loose soils, holds large amounts of water, increases aeration and slows the leaching of nutrients. It helps acidify alkaline soils for plants that prefer a lower pH. But this clean, odorless amendment is a nonrenewable resource, and centuries-old bogs are quickly becoming depleted. Besides that, dry peat moss is hydrophobic, causing any dry soil it is mixed with to be even more difficult to saturate.

An alternative to peat moss is coir, the dried fiber of coconut husks. A by-product of the coconut industry, compressed bricks or bales of coir can be found at well-stocked plant nurseries and online. Coir has all the positive soil-building characteristics of peat moss, but, unlike peat moss, coir can rehydrate easily and repeatedly. Coir is neutral to slightly acidic, naturally weed free, and helps retain and release water and nutrients over an extended period of time. When purchasing coir, look for “growing medium” not “mulch.” Coir mulch is also available, but it is too coarse to be of use as a soil amendment.

Generous applications of homemade or purchased compost increase sand’s organic matter and introduce populations of beneficial bacteria and fungi. The particle structure of compost helps bind sand particles together, making moisture and nutrients more available to plant roots by slowing the leaching process. Homemade compost makes use of materials usually discarded, such as grass clippings, leaves, kitchen waste, animal bedding and manures. It takes a bit of work to keep a healthy composting system going, and unless you have a small garden, it would be difficult to supply enough compost year after year for all your gardening needs. But a little is better than none. I make enough compost each year for one of my garden beds without too much effort.

Most animal manures add some nutrients to garden soil and help increase its organic matter. Fresh manures can burn the roots of young, tender plants, so it is best to compost them either by themselves or in a mixed compost pile. Fallen leaves are useful in the garden, but require nitrogen to break down their high-carbon composition. They will compete with your plants for any available nitrogen. So they, too, should be composted before being worked into your garden or flowerbeds.

Green manures are specific plants grown for the purpose of being turned into the soil while still green. The Chinese practiced this proven method for improving poor soil as far back as the fifth century B.C. Green manures prevent erosion, suppress weeds, conserve or add nutrients and supply organic matter. Increased levels of organic matter are associated with an increase in soil microbes (fungi and bacteria), some of which are natural enemies of plant nematodes. Because our sandy soils are usually home to several varieties of plant-parasitic nematodes, be sure that the green manure crops you grow do not foster their populations. Your County Extension can identify the types of nematodes in your soil and the green manures best suited for your area.

Sandy soils also benefit from organic mulches. They
conserve moisture, which slows the leaching of nutri-
ents. Mulches also add organic matter to the soil as they slowly decompose. But this decomposition can further deplete the naturally low nitrogen content of sandy ground. To counter this problem, apply a little cotton-seed meal, blood meal, fish emulsion or a thin layer of fresh grass clippings before you spread mulch. Depending on what plants you are mulching, bark and chipped wood, peanut hulls, pine needles, cottonseed hulls, grass clippings, hay or straw and leaves all make good mulches when properly applied.

Plants grown in sandy soil need to be watered more often, which leads to the leaching of plant nutrients that, in turn, leads to more frequent applications of fertilizers. Runoff and pollution from the overuse of fertilizers is a serious issue for Florida’s shallow aquifers. For this reason, it is important to improve the soil your plants are grown in. Organic fertilizers, those derived from natural materials, relinquish their nutrients more slowly than chemical fertilizers, and you can also purchase time-release fertilizers. Whatever type of fertilizer you use, your plants are better served by dividing the recommended dose into thirds or quarters and applying them over the growing season, instead of all at one time. Have your soil tested on a regular basis so you know its pH and nutrient levels to avoid excessive applications of fertilizers.

There are many ways to improve the structure and water-holding capacity of sandy soil that will lead to healthier plants. Because soil is a living entity, improving it is an ongoing process. Unless you build raised beds and fill them with expensive rich loam, or grow your plants in containers, there is no shortcut to improving sandy soil.

Dotti Hydue lives and gardens in rural Levy County.