Field Guide · Earth + Water
Cover crops, hardpan, and organic matter on sandy ground — straight answers.
Straight answers about building soil on sandy, nutrient-poor ground — the cover crops, the timing, and what the spade test actually tells you.
Sunn hemp (Crotalaria juncea). Its thick taproot and fast summer growth punch through compacted layers, and the roots rotting in place open the structure from below. Sow after the soil warms (May–June in central Florida) and cut 60–90 days later, before it flowers.
A summer crop like Sunn hemp fixes nitrogen as it grows and releases most of it as the residue breaks down. Figure two to three weeks after cutting before the bed is ready to plant.
No. Cut or crimp at flowering and leave the residue on top as mulch; the roots rot below and open the structure. Tilling undoes much of the work.
Do the spade test: dig a clean spadeful and look. A hard, plate-like layer under the topsoil, or water that sits instead of draining, means the bed is compacted below.
Grow it. Cover crops — Sunn hemp in summer, crimson clover or vetch in fall and winter — with the residue left in place. The fertility is grown in place: no bag, no truck.
Two to three weeks after cutting, then plant straight in. The residue feeds the top while the roots below keep opening the structure.
Deeper method: read the cover crops guide, or take the build sheet with you — Biological Soil Building PDF ($7).