Radishes are fun to grow. They're easy and provide almost instant gratification. They usually germinate in just a few days and are ready to eat in less than a month.
Radishes are cool-weather crops, best grown in spring and fall. Seeds can be planted four weeks before the last spring frost, and again in late summer or early fall. In the heat of summer, radishes quickly turn bitter and woody.
Standard radishes will mature in three to four weeks. To grow rapidly and achieve a nice shape, they must be thinned so the plants are no more than 2-3" apart. Do not give radishes a lot of fertilizer or your plants will have big tops and very little root.
Radishes come in a surprising variety of shapes and colors: pink, red, purple, violet, green, black and white. All grow fast and need to be harvested before they get too big.
Daikon, a Japanese radish known for its pungency, is bigger and slower-growing than standard radishes. It usually takes 50 to 55 days for them to reach full size. Daikon radishes can be pickled for winter use and are usually grown for a fall harvest.
Flea beetles are most problematic in early spring and they love to chomp on radish leaves. Use garden fabric (row covers) if you have problems with these tiny pests. Row covers will also deter cabbageworm. To help avoid pest problems, don't plant radishes in the same spot every year. Instead, rotate your plantings from one area to another.
Because radishes germinate quickly, some gardeners plant them among other crops, knowing they'll be harvested and eaten before the peppers or parsley needs the space.
Radishes turn bitter when large, so pick the entire crop as soon as it matures. Radishes store well in the refrigerator for a week or even two.