Growing Summer Radishes

Most radishes aren’t known to thrive in summer conditions, but careful selection and growing practices can produce good results.
By: Nan Chase

Botanical Name: Raphanus sativus

Since most maturing radishes typically don’t give good results in hot summer weather, gardeners should be careful to select the right varieties of radish to plant for summer harvest. Growing summer radishes is not for the faint of heart, but can be rewarding with a little extra attention.

Summer radish cultivation begins in spring. Most varieties of table radishes – those familiar dark-pink globes packed with tangy flavor – are planted in early spring or late summer, when the soil is cool. They germinate within a week, and produce mature edible roots in three to fourweeks. That fast!

You will know those so-called spring radishes if they are described as reaching full size in 18-30 days. Plant seed in early spring, harvest before summer begins. Or, plant in late summer and harvest in autumn.

There is also a category of radishes that are planted in mid-summer, as seed, and then grown for two to four months for a late fall or early winter harvest. They are often called winter radishes.

Trying to grow radishes for summer harvest – summer radishes -- means finding the radishes that can stretch the typical short spring season, namely, radish varieties described as reaching full size in approximately 30-45 days. You will plant those seeds along with the earlier maturing varieties, but harvest the roots a bit later.

Seed catalogs and seed packets will mention several key phrases that indicate a possible summer harvest, including “slow to bolt,” “resists woodiness,” and “resists pithiness.”

That’s because a downfall of radishes growing in too-hot soil is a tendency for the roots to get tough or to bolt to seed prematurely.

Try some of these summer-friendly radishes:

  • Rover Hybrid, 21 day maturity but specially bred to resist summer heat
  • Crimson Giant, 30 day maturity but doesn’t get pithy ever
  • Dragon Hybrid, 40-45 day maturity and grows to four or five inches long
  • Black Spanish Round, 55 day maturity, with deeply colored skin and delicious white flesh
  • Giant of Sicily, an Italian native that grows up to two inches across but stays tender
  • Rat-tailed radish, 50 day maturity, grown for the tangy seed pods rather than the root, this unusual radish takes center stage at the height of summer

In addition, there are two radishes that may do fairly well in summer if pampered, although mainly they are known as winter radishes:

  • Daikon Minowase, 60 day maturity, for possible planting in late spring rather than summer
  • Watermelon, 60 day maturity, a radish with pink flesh and the same planting strategy

All radishes need well-worked, fertile soil, and even moisture, but the summer radish needs a bit more care: very light weeding, so that delicate roots aren’t destroyed, and a layer of straw mulch to keep the soil as cool as possible. And give them a little extra water if rain is scant.

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