Radishes

Cruciferae Family
Raohanus satvus – Radishes

Spring radishes, the first crop recommended for most children’s gardens, may be one of the easiest foods to grow, but not easy to grow well. Most varieties germinate quickly and success or failure at harvest time comes within 20 to 40 days later, often as not with disappointing results. Because quickness rather than inherent taste appeal is the primary reason for recommending radishes for all children’s gardens, let’s look at the conditions required to grow the kind you want to eat, or offer to someone else.

Quickness cuts both ways, for and against the gardener. If all conditions are optimum for sprouting, growing, bulbing, and maturing, the rapid growth rate produces a flavorful, edible radish root. If all conditions are not met, the resulting bulb (if there is one) can quickly become far from palatable.

Germination - Seeds will germinate in three-to-ten days with soil temperatures between 45-95°F. For normal sized radishes, plant seeds ½” deep and 1 ½” apart. For larger sized roots, plant seeds 1 ½” deep and 2” apart. If seeds are planted too close together, you will have to thin the young plants to get good root growth.

Growth - Once the seeds have germinated, the temperature range required for quick, edible bulb growth becomes quite narrow. Optimum temperatures for growth are 60-75°F, with some varieties able to tolerate temperatures in the low 80s°F. Colder temperatures (below 55°F) will result in slow growth and produce small, bitter and inedible bulbs. Warm temperatures (above 80°F) accelerate growth, prevent cell tissues from sticking together, and result in pithy, inedible bulbs.

Timing - I have seen radishes planted in starter gardens at all times of year with a large percentage of inedible roots as the result. A look at the temperature charts for southern New Mexico reveals only two short planting windows that are optimum for radishes. If you grow spring radishes at other times of year, your radishes may be less than palatable.

Soils - For good growth, radishes needs soils that is moderately rich in nitrogen, phosphorus and potassium. The potassium level in our local soils is naturally adequate, but adding nitrogen and phosphorous is advisable. For organic growing, a combination of compost, fish emulsion, and bone meal will suffice.

Harvest - Because they are fast growing root crops, radishes do not hold well in the ground. Pay attention to the ‘days to maturity’ as listed on the seed packet and be ready to harvest. A few days too late will reduce flavor and texture. Without their green tops radishes will store longer in the refrigerator than in the ground, so go ahead and harvest on time.

Problems
• Flea beetles will attack the young plants making small holes in the leaves. The solution is to make sure the radishes can out grow the flea beetle feeding.
• Little or no root bulbing can be caused by crowding, too compact a soil (as in heavy clay soils), insufficient phosphorous, or by lack of adequate sunlight. The solution is to start over and correct the problem in the next planting – you cannot rescue spring radishes!
• Bolting – going to flower instead of bulbing is caused by plants being exposed to more than 12 hours of daylight. Stay within the spring and fall planting schedules for best results.

Other Types of Radishes - Not all radishes fall into the spring radish category. Daikon radishes are more heat tolerant than the spring varieties and take 40-70 days to mature. Their flavor is milder than most small radishes and they are commonly used in Asian recipes. The Black Spanish radish is a winter radish that can be planted in late summer and takes about 70 days to mature. It is a ‘storage’ radish, meaning it needs to be stored for a couple of months to become edible. Both daikon and winter radishes are biennials that bloom in their second year of life.

After more than 2,000 years of cultivation, the radish is still top of the list for young gardeners to learn the lessons of sowing and reaping. Now that we are equipped with an understanding of the plant’s requirements for optimum growth, our children’s and our own gardens will more dependably produce tasty radishes for the table.

till next month,
Good Gardening and Good Eating

Darrol Shillingburg
Doña Ana Extension Master Gardener
August 20, 2010