White Clover

White clover is what you plant when you want nitrogen without having to buy it. A well-established stand can fix fifty to a hundred pounds of nitrogen per acre each year — pulled straight out of the air by bacteria living in nodules on the roots — and deposit it into the soil as the roots turn over. It is the living mulch that fruit growers plant in orchard alleys and home gardeners tuck between raised beds, and once it takes hold it can persist for years with nothing more than an occasional mowing.

The trick is getting it established in the first place. White clover seed is small — smaller than a tomato seed — and the seedlings are slow to start. Broadcast into a firm, weed-free seedbed about four weeks before your last frost, rake lightly to barely cover the seed, and press it down with the back of a rake or by walking over it. The seed needs good contact with the soil to germinate, and loose soil means poor germination. Then wait. The seedlings are tiny and unimpressive for the first month, and weeds tend to grow faster. If you sow into a bed that is already full of chickweed or annual grasses, the clover usually loses — shaded out before it can form a canopy. Starting with clean ground is worth the trouble.

Once white clover is up and established, it spreads by stolons — horizontal stems that root at the nodes and form a persistent mat. It tolerates foot traffic better than most cover crops and can handle being mowed repeatedly without dying back. That resilience is useful in pathways and under fruit trees, but it also means you need to stay on top of it if it starts creeping into beds where you don't want it. Mow before the flowers go to seed — usually in late spring and again in midsummer — to prevent it from self-seeding aggressively into vegetable rows.

White clover blooms from late spring into fall, and the flowers are a reliable draw for bees and other pollinators. That is often cited as a benefit, and it is, but it also means that mowing a bed of clover in full bloom will temporarily displace every bee in your garden. Mow in the evening when they've gone home, or wait until the flush of bloom has passed.

In hot, dry summers, white clover tends to go dormant — the foliage yellows and the plants appear to stall. This is not a failure; the plants are waiting for cooler, wetter weather, and they usually green back up in late summer or early fall. If you need consistent ground cover through a dry July, a grass-clover mix may perform better than clover alone.

The main long-term issue is overenthusiasm. White clover is persistent, and if you let it seed freely it will show up in places you did not plant it — between carrots, in the lettuce bed, tangled around the base of tomato cages. Once it roots in a vegetable bed it can be difficult to remove completely without digging. The solution is vigilance: mow before seed set, and pull any volunteer seedlings that show up where they are not wanted.