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
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
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.
• 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
• 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
Doña Ana Extension Master Gardener
August 20, 2010