How-To · Sandy Soil · The Southeast

Gardening in Sand

Plants that want the soil you apologize for: how sand behaves, the one planting habit that kills more sandhill natives than drought ever does, and a simple plan for turning the hottest, driest bank on the property into the best-smelling bed you own.

8 min read · By Fiona von Grey · Aiken, South Carolina

IWhat sand is actually doing

We garden on sand in Aiken. Not a sandy loam, not a soil with a bit of grit in it, but the deep, pale, loose stuff of the Carolina sandhills, which runs through your fingers when dry and drains a bucket of water before you have finished pouring. For years the standard garden advice about ground like this has been some version of an apology followed by a truckload of compost. We think that advice gets it backwards for a whole category of plants, and a beautiful one.

Sand is made of large mineral particles with big spaces between them. Water runs straight through those spaces, taking dissolved nutrients along, and air fills in behind. That makes sand dry, lean and very well aerated, and it warms quickly in spring. For a hydrangea, a hosta or a lawn, those are all problems. For a plant that evolved in the longleaf sandhills or on a coastal dune, they are the conditions of home, and the plants have their own answers: deep roots that follow water down, small or needle-like leaves that lose less of it, fine hairs or waxy coats against glare, and aromatic oils that make the foliage unappetizing.

The scrub mints, the calamints, false rosemaries and wild pennyroyal in our field guide, are the clearest example we grow. They do not merely tolerate sand. Put them in rich, moist garden soil and they rot. The trick to growing them is not to fix the ground. The trick is to leave the ground alone.

The trick is not to fix the ground. The trick is to leave the ground alone.

IIThe mistake almost everyone makes

You dig a hole, and because you are a kind person and the plant was not cheap, you fill the bottom and sides with compost or bagged garden soil and set the plant into that. It looks like care. In sand, the effect is to build a small sponge inside a sieve.

Water moves easily through the surrounding sand until it meets the fine, spongy material in the hole, which holds onto it. The roots now sit in the one wet spot in the bed, often for days after every rain, and they sit there through a mild, damp Southern winter when the plant is using very little water at all. The University of Georgia's extension service lists wet soils, overwatering, overfertilizing and poorly draining planting sites as the conditions behind root rots caused by Pythium, Phytophthora and Rhizoctonia. That is the usual end of an overly well-loved sandhill shrub. The plant looks fine all fall, goes a little dull over winter, and does not come back in spring.

Clemson's Home and Garden Information Center, which is not a source prone to shouting, puts the rule in capital letters: do not amend the backfill. The advice holds for most woody plants. For sandhill natives, the advice is the whole game.

IIIPlanting a sandhill shrub, step by step

IVThe first year, and every year after

Water while they settle, then taper

University of Florida extension advice for establishing plants in sandy soil is to water lightly and often at first, until the roots can live on rainfall. In practice: for the first two or three weeks after fall planting, water when the top of the root ball is dry, which in sand may be every two or three days in warm weather. Over the next month or two, stretch the intervals out. By winter, leave the plants to the rain. Through the first summer, give a deep drink in a long dry spell. After that, most years, stop.

Expect a sulky start

Sandhill shrubs put their first effort into roots. The top may barely move for months. That is normal, and it is not a request for fertilizer. A plant pushed into lush growth in the first spring is often a plant lost by the second.

Shear lightly, and at the right time

Most scrub mints stay denser with a light shear after the main flush of flowers, or in late winter before growth begins. Take off a third at most, and do not cut back into bare old wood.

Keep the sun on them

In the wild, fire kept these ridges open. In a garden, trees and neighboring shrubs fill in year by year and a bed in full sun slowly becomes a bed in half shade. Every couple of years, stand where the plants are at midday and look up.

VIf your soil is not sand

Plenty of Southeastern gardeners are on red clay, and clay is the opposite problem: fine particles, little air, water that sits. You can still grow many sandhill natives. What you cannot do is dig a hole in clay, fill that hole with sand, and plant into it; that makes a bathtub, and a bathtub full of sand is still a bathtub.

Build up instead. A raised bed, a broad mound, or a berm of coarse sand mixed with fine gravel, sitting on top of the existing ground and a good foot or more high, gives roots somewhere to live above the wet. A south- or west-facing slope, a bed along a hot driveway, the top of a retaining wall, or a crevice between stones all do the same job. And choose the most forgiving plants first. Georgia savory, Clinopodium georgianum, takes heavier soils than any other plant in the group, and the hybrid 'Desi Arnez' puts up with a wetter winter than most. Leave Cumberland rosemary and gray false rosemary for the sandiest, best-drained spot you have.

VIA plan for the hot bank

Nearly every property has one: a sunny slope, a strip along the drive, a bed at the edge of the street where the hose will not reach. Here is a planting built entirely from plants that want to be there. Quantities are for a strip roughly twelve feet long and five feet deep; scale to suit.

In South Carolina, swap the front edge for Cumberland rosemary, Conradina verticillata, where the bed tumbles over a low wall or the lip of a slope; the plant is sold inside the state only, for reasons we explain in a separate piece. On the coast, gray false rosemary in place of Georgia savory will take the wind once established. For a more Mediterranean note, a culinary rosemary at one end shares every requirement on this list. Plant the whole strip in fall, water through the first weeks, and by the second summer you should not need to think about the bed at all.

VIIQuestions we get asked

Should I add anything at all to sandy soil?

For sandhill natives, no. For vegetables, roses and most conventional garden plants, organic matter worked broadly through a whole bed is a different matter and often helps. The harm comes from amending a single planting hole, and from feeding plants that evolved on lean ground.

What about drip irrigation?

Useful for the first season if you are away a lot, on a separate zone and set to water less often than you think. Turn it off once the plants are established. An automatic system running on a lawn schedule is the most common way we hear of sandhill shrubs being lost.

Is gravel mulch too hot?

Not for these plants. A thin gravel mulch keeps the crown dry, reflects light up into the foliage, and looks right with the fine textures of the sandhill flora. Pine straw is the softer, more traditional choice in the Southeast and also works well.

My plant looks dead after the first winter. Is the plant gone?

Scratch a stem gently with a thumbnail. Green underneath means alive; semi-evergreen species like scarlet calamint thin and drop leaves in a cold winter and leaf out again in spring. Wait until late April before giving up, and resist the urge to water a plant that is only resting.

Further reading on The Node

Every scrub mint we grow is in the field guide to the scrub mints, and the story behind them is in The Rosemary That Isn't. For a wider palette of plants for dry ground, read Gardening for the Dry Years, and for the timing argument, our fall planting guide for the Southeast.