Tillage Radish (Daikon Cover Crop)

Walk the bed in early spring and look for plants that came through alive and are sending up a flower stalk. Cut, pull or hoe them off before the pods fill. In a cold winter you will find none and can plant straight into the clean, mellow bed the rotted roots leave behind. Radish is meant to winterkill, and it dies at about 25 F, showing injury once temperatures drop below the mid-20s. Mild winters and warm zones can still let roughly 10 percent of a stand survive, and a survivor bolts, sets seed and reseeds itself into a weed you did not plan on. Do the walk even after a winter you thought was cold enough.

Lift roots about 7 weeks after sowing for a spring crop and about 10 weeks for a fall one, taking them while the shoulders are still smooth. Left as a cover crop, harvest nothing and let the freeze do the work. An overmature daikon turns fibrous and its flavor sharpens until it is unpleasant. Fall roots take longer than spring roots because they are growing into cooling weather.

Count back from your average first frost and sow with at least 6 weeks of growing weather left. Drill seed 1/2 to 1 inch deep, or broadcast and rake it in. For a cover crop stand, drill about 6 to 10 pounds per acre or broadcast 8 to 12 pounds per acre, roughly a quarter pound per 1000 square feet. Mixing with oats or cereal rye protects the soil surface that radish alone leaves loose and bare, and rye has the added benefit of overwintering to catch the nitrogen the rotting radish releases. The whole point of this plant is the taproot, and the root is built in the cool weeks of fall. Sown too late it never bulks up, and sown too early in midsummer heat it bolts and sets seed, which turns next year's cover crop into next year's weed.

Water on a steady 2 to 3 day rhythm rather than letting the bed swing dry and then soaking it. Do not let it flood either. This crop tolerates neither drought nor standing water. A dry spell gives roots a rough texture and off flavor, too much water rots them, and the swings between the two are what bring on radish scab.

Radish and radish mixtures need roughly 40 to 60 pounds of nitrogen per acre, about 1 to 1.5 pounds per 1000 square feet, and that total can be met from fertilizer, manure or legume credits. Following a manured or well fertilized summer crop the credits usually cover it and you add nothing. On thin or long-fallow ground with nothing left to scavenge, supply the shortfall before sowing. This plant's job is to catch the nitrate your summer crop left behind before winter rain leaches it away, then hand it back in spring as the roots rot. A well grown stand takes up more than 100 pounds of nitrogen per acre (eOrganic). Nitrogen you add beyond what the stand needs is simply more nitrogen available to leach.

Growing this as an edible daikon rather than a cover crop means thinning seedlings to 4 to 6 inches apart in rows once they have their first true leaves. A cover crop stand is left thick and unthinned on purpose. A daikon root needs room to size up without a neighbor pinching it. Crowded roots stay thin and forked, which is fine for shattering hardpan but poor eating.

Look over the seedlings for the shot-hole feeding of flea beetles and for wilting that points to cabbage root maggot. Do not sow this where broccoli, cabbage, kale or other cole crops grew, and do not follow it with them either. Radish is a brassica, so it shares clubroot, cabbage root maggot and flea beetles with every cole crop in the garden. Slotting it into a cabbage rotation feeds those problems instead of breaking them.