Radishes (Raphanus sativus) are often at the top of the list of easy-to-grow vegetables, but it took me years to learn how to grow great radishes, which can actually be quite finicky. Small problems can combine to cause radishes to lose interest in plumping up, so attention to detail is needed. It is also important to make use of both radish seasons – spring and fall. Organic gardeners have even more reasons for growing radishes, because this humble vegetable also can be used to manage pests, suppress weeds, or improve the soil.
Spicy Spring Radishes
My biggest beginner’s mistake (which I repeated many times) was to plant my first radishes too early in spring, while the soil was still cold. The seeds would sprout well enough, but interruptions in growth from changeable spring weather took its toll on the crop. I would get some good radishes, but many plants refused to form good roots. I have since learned to be patient and never start planting spring radishes more than a month before my last spring frost date. The best spring radishes grow when the soil is still cool, but days are getting steadily warmer.
Radish seeds are fast, sure germinators, so thinning seedings to at least two fingers apart is a required step. Beyond thinning, spring radishes must be kept constantly moist; a little wet is better than a little dry. In my experience, consistent moisture is the essential key to growing radishes in the spring.
Many gardeners use some of their spring radishes as trap crops for flea beetles, which theoretically draws hungry flea beetles away from arugula, spring cabbage, or other high-value crops. But for this or any other trap crop scheme to work, the problem insects must be trapped or killed rather than being allowed to disperse through the garden. To gather flea beetles from radish foliage, the best tool is a hand-held rechargeable vacuum, such as those used to remove pet hair from furniture.
Radishes are widely hailed as a companion plant to repel cucumber beetles and other squash family pests, but they work best when combined with a second companion plant such as buckwheat. Used together, the radishes repel cucumber beetles while the buckwheat attracts beneficials, which serve as further deterrents.
Mellow Fall Radishes
I grow more radishes in fall than in spring because they are just plain better. Instead of becoming unpalatably hot the longer they stay in the ground, the flavor of fall-grown radishes mellows as soil temperatures drop. Meanwhile, the roots get bigger yet stay wonderfully crisp.
Eating even the best raw radishes gets tiresome quickly, but not so with cooked radishes, which are rather like sweet turnips, only with more color. Autumn radishes do sometimes have cosmetic problems caused by random chewing by weevils and wireworms, but skin imperfections disappear when the radishes are cut up and cooked. At our house, we roast chunks of big fall radishes along with other vegetables, or stir-fry them for Oriental dishes.
The Daikon Dilemma
Oriental daikon radishes (Raphanus sativus var. longipinnatus) are one of my favorite fall crops. In addition to eating the long, lovely roots (cooked, please), daikon radishes produce an abundance of foliage for composting. I make several small planned sowings of daikon radishes, and use them as a fill-in crop when other fall planting plans go asunder. Weeds don’t have a chance once the daikons get going, and I love the way the roots push up out of the ground when they reach perfect condition for harvesting.
Daikon radishes are at peak eating quality when they are less than 12 inches (30 cm) long, but many varieties will continue to grow much larger if allowed to stay in the garden until cold winter weather causes them to die back and start rotting. This is what you want to happen! When you use daikon radishes as a cover crop, the deep, stout roots rot over winter, creating a vein of organic matter that extends beyond your typical cultivation zone. As a "bio-drill" crop to improve soil tilth and health, daikon radishes have it all – they suppress weeds at the surface, penetrate compacted subsoil, and can easily be killed by chopping off their heads in climates mild enough to permit their winter survival.
Which daikons to eat, and which to allot to the soil? The dilemma will never go away, but it is most easily handled by simply growing plenty of daikon radishes every fall.
By Barbara Pleasant