It’s tempting to imagine, when planting a row of spring radishes, that they will be ready in perfect shape at harvest time, free from blemishes, and wholly uniform in size and shape. Typically, though, this is not the case. There are a number of common radish problems that can result from environmental impacts and a handful of garden pests. And there are some practical measures the home gardener can take to minimize them.
A commercial radish grower who contracts with grocery store distribution might opt for one of the hybrid varieties that have been bred for uniform growth. These tend to produce radishes of the same size and shape, and the crop is ready all at once. Open pollinated varieties, just by their nature, may have a greater variability in size, shape, and growth rate. A good example is Easter Egg II, which is actually a single variety with highly variable skin colours.
Radishes are a cool season crop that work best in the spring and fall, before the soil becomes warm. They’re also a very fast-maturing crop, usually taking fewer than 30 days to mature. The exception are the daikon radishes, which are much larger, but still very fast growers. Bolting is the plant’s response to increased soil temperature (or other stresses), that causes it to “run to seed.” This is a very sudden transition from regular growth to flower and seed production. The flower stem can appear in only a couple of days. Once the flowering process begins, the leaves may become hairy and bitter tasting, and whatever root has developed may become woody. The trick is careful timing in the cool season, and regular monitoring of the crop.
Like carrots, radish roots are prone to cracking in situations when the soil moisture is uneven. The root needs to develop at a steady pace. A period of dry soil may cause it to contract slightly. If this is followed by ample moisture, the plant is not able to cope with absorption, and may split as a result. The solution is to keep the radish bed evenly moist with very regular watering. Don’t skip a day or two and then flood the bed. Consistent moisture will minimize splitting.
Multiple tap roots
While this can happen when excess potassium is out of balance in the soil, it’s more likely a response to the plants being crowded and competing for moisture and nutrients. It’s important to thin radishes (and carrots) so each plant has adequate space to develop in the row.
Little chips that appear on the upper side of the above-ground portion of a radish can be caused by a number of animals. Slugs, woodlice, mice, and even birds can cause this sort of damage. If the scars are quite shallow, they are more likely due to the rasping mouthparts of slugs or woodlice. If there are chunks or bites taken, look to larger creatures as the culprit. Row cover and mesh is available that will act as a physical barrier between the pest and the crop, but it needs to be placed more or less at the time of planting. Damage as shown in the photo above is quite cosmetic, and can be peeled away with a paring knife.
Root nibbles and holes
A fairly wide range of soil-dwelling insect larvae can cause damage to the below-ground portion of radishes. The primary villain is the root maggot, the larva of a small fly. To prevent root maggots, use Lightweight Floating Row Cover, to prevent the adult from laying eggs on the newly seeded bed. Apply the fabric at the time of sowing for the best protection, rather than once the seedlings emerge. The adult fly is attracted to the damp soil of the seeded bed.
Numerous small holes that appear to be shot through the leaves of radishes (and other crops) are caused by flea beetles. Use Lightweight Floating Row Cover at the beginning of the season to prevent them.