How to Grow Radishes in the USA

Quick Facts

Factor	Value
Soil pH	6 - 7
Sunlight	6-10 hours direct sun
Germination temp	45°F (7°C)
Optimal growing temp	54-79°F (12-26°C)
Minimum survivable temp	50°F (10°C)
Time to harvest	25-56 days
Drainage	RHS: "Choose an open, sunny site, although light shade is acceptable for salad radishes in midsummer"; prepare soil to a fine texture and remove stones.
Lifecycle	hardy annual; withstands heavy frosts in spring and autumn
Edible parts	roots, leaves (winter and oriental types), seed pods (edible-podded types)
Documented problems	1 disease, 6 pests

At a Glance

Salad Radish or Winter Radish: Which Should You Sow?

"Radish" covers two genuinely different crops. Salad (summer) radish is sown shallow -- about 1cm deep, 2.5-5cm apart -- germinates in 7-10 days, and can be ready to pull in as little as four weeks. Winter and oriental types (daikon, mooli and similar) are sown deeper, at 2cm, spaced much further apart at 15-20cm, and take at least eight weeks to build a far larger root over a longer season (RHS).

Both share the same broad sowing window, so the choice is about what you want: quick, continuous salad pickings, or a bigger root that stores. Because salad radish matures so fast, sow small batches every few weeks rather than one large sowing -- that keeps a continuous harvest coming instead of one glut followed by a gap.

Soil & Growing Conditions

Water: RHS: "Keep the soil consistently moist" and water "during any dry spells". Univ. of Maryland: "keep evenly moist but not wet".

Growth Stages

Harvest & Storage

When to pick: RHS: salad radishes are ready at "about 2.5cm (1in) in diameter". Univ. of Maryland: "Harvest spring radishes when they are about one inch in diameter, depending on the cultivar, and before they crack, become pithy, or too hot".

How Do You Know When to Pull a Radish?

Watch the shoulder, not the calendar. RHS gives salad radish as ready at about 2.5cm (1in) in diameter; University of Maryland Extension independently gives the same figure -- "about one inch in diameter, depending on the cultivar" -- and adds the real warning: pull before roots crack, turn pithy, or get too hot to enjoy. A root grown too slowly, or left too long, goes from crisp to woody and unpleasantly sharp.

In practice that means checking the shoulder -- the top of the root, visible where it swells at the soil surface -- rather than waiting for a fixed number of weeks. Once it reaches roughly golf-ball width for a salad type, it is ready to pull.

Diseases

Pests

Companion Planting

Sources

1. Clemson Cooperative Extension - Cabbage, Broccoli & Other Cole Crop Insect Pests

   Diamondback moth is "the most serious insect pest of brassica crops in South Carolina", leaving a window-pane appearance where the upper leaf surface stays intact. Damage is quantified relative to each other: one cabbage looper does roughly the damage of 5 diamondback moth larvae, and imported cabbageworm about two-thirds of a looper. Cross-striped cabbageworm hatches in masses and can rapidly skeletonise a plant, dropping to pupate just under the soil surface. Cabbage webworm damages buds and growing points, causing lateral budding. Cabbage aphids are commoner in cool autumn weather. Flea beetles are most problematic on mustard and turnips, which lack the protective waxy coating.

2. Clemson Cooperative Extension - Carrot, Beet, Radish & Parsnip
3. NC State Extension Gardener Plant Toolbox - Raphanus sativus (Daikon, Forage Radish, Mooli, Radish, Rat's Tail, Tillage Radish)
4. University of Maryland Extension - Growing Radishes in a Home Garden

These 4 sources are specific to this region. The full list of 9 sources behind this guide (Clemson Cooperative Extension, FAO EcoCrop, NC State Extension Gardener Plant Toolbox and others) is in the references of our UK guide to radishes; they describe the plant itself, which is the same wherever it grows.

Can You Regrow a Radish From Its Top?

You can regrow the leaves, not the root. Cut the leafy top off a radish with an inch or so of the root still attached, stand it in a shallow dish of water, and it will sprout fresh green growth within days — useful for salad leaves, but it will not swell into a new radish.

The reason is the same one Oregon State University Extension gives for carrots, a close relative of the same swollen-taproot design: "Once the taproot is removed it cannot grow another," because cutting off the root removes its one growing point, while the growing tip that produces leaves stays behind on the top and can only make more leaves and thin fibrous roots. OSU's answer addresses carrots specifically, not radish by name, but the same root anatomy applies — and no radish-specific institutional source was found to confirm or contradict it directly.