Turn over your garden soil in spring and an earthworm often comes wriggling up on the edge of your spade. The soil around it is unusually dark and crumbly—a sign that worms pass through often. Beds with plenty of earthworms have soft soil that drains well. Lately, researchers in a number of countries have been working hard to find earthworms that hold up against heat and drought. As the weather turns harsher, this small animal that keeps soil healthy only becomes more valuable.
What earthworms do in the soil
Earthworms eat organic matter—fallen leaves, bits of root, kitchen scraps. What they digest and leave behind is called castings. Castings hold several times more nitrogen, phosphorus, and potassium than the surrounding soil, all in forms plants can use right away. They're also far richer in the microbes that keep soil alive.
As earthworms travel through the ground, the tunnels they dig let water and air seep deep down. Rain drains instead of pooling, and even in dry spells some moisture lingers around the roots. Because worms mix organic matter into the soil and carry it downward, nutrients from the topsoil reach the depths where roots can find them. That's why a bed full of earthworms grows well with hardly any extra fertilizer.
Why we need a tougher earthworm
Earthworms struggle when soil dries out or temperatures climb sharply. In a long drought they burrow deep and go dormant, and if it dries further they may not survive. They're sensitive to pesticides and chemical fertilizers too. As summers grow longer and hotter, more and more gardeners are watching the worm populations they worked to build shrink at the height of the season.
So researchers are selecting and raising strains of earthworm that tolerate heat and dryness. The red wiggler, common in food composting, is a leading candidate. It's still too early, though, to point to any one variety as clearly superior. If a reliably hardy earthworm can be developed, it should help hold soil vitality even in beds that see frequent drought.
How to grow more earthworms in your garden
Rather than buying worms and dropping them in, you'll get longer-lasting results by building soil they want to live in and letting them come to you. Try a few of these today.
- Lay organic matter on top of the soil. Fallen leaves, grass, and well-aged food compost all feed earthworms.
- Don't turn the soil often. When their tunnels collapse, worms move elsewhere.
- Keep the soil from drying out completely. A cover of straw or leaves holds moisture in longer.
- Cut back on pesticides and chemical fertilizers. Worms are the first thing to disappear when they're overused.
If you garden on a balcony, set up a small worm compost bin. Add your kitchen scraps and castings will build up; mix that soil into your pots.
Before you leave the garden today, scatter a handful of fallen leaves over the soil. Once the earthworms gather, the soil gets better all on its own.
Sources: soil biology research on soil invertebrates and castings nutrition; Rural Development Administration materials on earthworms and soil improvement.
