Radish

History

Radish is a root crop and member of the Brassicaceae family, also known as the cabbage family, which includes other cool season crops like cabbage, kale, collards, broccoli, and cauliflower (Figure 1).

The name radish comes from both the Latin word for “root” and a Greek expression that translates to “easily reared.” Western Asia (likely China) is considered the country of origin for the wild form, and it was first recorded around 2000 B.C. in Egypt. Radish was especially popular with the Greeks and very highly regarded. The original radish was probably larger and slow-growing, similar to Daikon radish.

By the 16^th century the smaller, faster-growing radish was recorded in Europe, likely introduced by the Romans. Radish was the first crop introduced by Christopher Columbus to the Americas but was already being produced in Mexico and Haiti. Radishes were also grown by early English colonists in Massachusetts by 1629, and have remained popular in the U.S. See Figure 2.

The large daikon radish is most popular pickled in Japan and China (and a major part of these countries’ diets), while salad radish is more popular in Europe and the U.S.

Varieties

Radishes are annuals or biennials and grouped into two main categories: (1) daikon and (2) salad. Daikon radishes include larger, Asian varieties with long, white cylindrical roots that are great winter storage crops. Salad, or spring, radishes include varieties that are faster-growing with small, round roots and are traditionally red-skinned with white flesh (although available in a variety of colors). Icicle radish is a longer variety of salad radish. French Breakfast and White Icicle radishes are great varieties for warmer climates like Louisiana as they are slow to bolt. Radish is primarily grown for its round or cylindrical roots; the green tops are also edible but best cooked rather than consumed raw (due to their coarse texture).

Radishes have either open-pollinated (including heirloom) or hybrid varieties. Some radishes are heirloom varieties, such as Black Spanish and French Breakfast, meaning the seeds have been saved for at least 50 years, can be saved each season and replanted, and are open-pollinated. Radish flowers are perfect (having both male and female parts) and are usually open-pollinated. If saving seed, different varieties should be separated by a distance of 300 feet-1/2 mile to avoid cross-pollination. Generally, it is not recommended to save seed for future planting with hybrid varieties as they are usually not expressed properly in the next generation.

See the recommended radish varieties for Louisiana in Table 1.

Table 1. Recommended Radish Varieties for Louisiana

When and How to Plant

While radish varieties do vary in taste and texture, it is a misperception that all radish varieties are hot/spicy. Since this is a cool season crop, this often unpleasant taste occurs when a radish has inadequate moisture, experiences warm temperatures that cause bolting, or is overmatured. To prevent a hot/spicy radish, plant this crop during the recommended planting dates of the cool season and select shorter harvest varieties when planting a spring crop. Generally, it is best to avoid planting daikon radish during spring planting dates since the longer harvest time may result in bolting as the warm season approaches. Daikon radishes, along with some slower-growing salad radish varieties, are best planted during fall planting dates and are great winter storage crops.

Radish should be direct seeded outside during the recommended planting dates (refer to the Radish Planting Guide, Table 2). Radish seeds will germinate in soil temperatures of 45-90 degrees F, but as a cool season crop, the optimum growing temperature for best-quality crops is 50-65 degrees F. The use of a soil temperature map can help guide planting decisions.

Sow salad radish at a shallow 1/8-inch depth. Scatter seeds in a furrow down the row, lightly cover with soil, and water in. Seeds should emerge in 4-6 days and seedlings should be thinned early to allow 1-inch spacing between plants. For Black Spanish, Watermelon, and White Icicle radishes, thin to allow 2-4-inch spacing between plants since these are larger varieties. See the Radish Planting Guide below.

Sow daikon radish at a similar shallow depth (1/4 inch) but scatter seeds farther apart in a furrow down the row, since they will need to be thinned to 6 inches between seedlings (see Radish Planting Guide below). Cover lightly with soil and water in; seedlings should emerge in 4-11 days.

For a continuous supply of radishes, direct seed outside every 10-14 days. Radish is moderately frost tolerant but will bolt during warm temperatures and longer days. Varieties such as Watermelon and Black Spanish, along with daikon radish, are best grown as a fall crop.

Table 2. RADISH PLANTING GUIDE

Where to Plant

Plant radishes in loose, well-drained soil in full sun (6 hours/day), although they may tolerate partial shade. A soil pH below 6.5 puts radishes at a higher risk for clubroot disease. It is recommended to plant radishes in box beds or in traditional raised garden rows that are about 4-6 inches tall to ensure good drainage and allow for root formation. In all types of gardens, it is recommended to add a layer of compost, peat moss, rotted hay, or other organic matter and mix into the soil to optimize plant health.

Salad radish needs very little space and matures quickly, so consider intercropping (or interplanting) with slow-growing crops like onions, cucumbers, tomatoes, peppers, and squash. Avoid intercropping with other Brassicas as they may attract flea beetle pests.

Each season, rotate plant families — avoid planting crops from the same plant family in the same area of the garden — to reduce disease and pests. For radishes, the recommendation is every 2-3 years to reduce risk of clubroot.

Plant Care

Watering

Radishes require adequate moisture, or they may become hot/spicy, woody, or pithy. Generally, they require relatively low irrigation aside from germination and rapid growth stages. Water thoroughly weekly if it doesn’t rain, aiming for 1 inch per week.

Fertilization

As in many cool season root crops, insufficient boron may cause distorted growth, internal browning, and scabby growths on the surface of radishes. Conduct a soil test for micronutrients if these problems occur, and discuss the results with a local county extension agent. If unsure about the nutrient status of your soil, repeat soil testing every 3 years.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Alternatively, a synthetic fertilizer may be used at a rate of about 1.5 lbs (3 cups) of 13-13-13 for every 25 feet of row or 75 square feet. Broadcast, or sprinkle evenly, over the soil and then mix in about 3-6 inches deep using a rake. For long-growing daikon radishes, supplemental sidedressing, or reapplication of synthetic fertilizer, is recommended 3-4 weeks after planting. Sidedressing is the addition of fertilizer to the soil around already established plants when the plant begins to fruit or vine, primarily to provide nitrogen. When using synthetic fertilizer, sprinkle lightly around each plant, keeping it a few inches away from the plant stem; water into the soil. Additional sidedressing may be applied every 3-4 weeks. Fish emulsion is a good, quick-release source of nitrogen for sidedressing if using organic fertilizers.

Mulching

Mulch (plastic or organic) is recommended to aid in moisture retention and to control weeds for daikon radish since this type is slower to mature. Plastic mulch is not recommended with radishes as this crop is very closely spaced.

Weeds: Remove weeds carefully by hand or using hand tools to promote plant health, especially for daikon radish since this type is slower to mature. Weed pressure may be lowered with crop rotation.

Insect Pests and Diseases

Since most radishes are very quick to mature, insect pests and diseases pose less of a problem than for other crops. Daikon radish is more susceptible to insect pests and diseases due to a longer growing time. Refer to Table 3 to aid in diagnosis and management of common radish insect pests and diseases.

Table 3. Organic and Natural Management for Common Radish Insect Pests and Diseases

Harvest and Storage

It is best to harvest radishes when they are young, rather than overmatured, since they will become hot/spicy, pithy, and woody. The root top should be visible above the soil. Daikon varieties will take longer to mature and fall crops should be harvested before the ground freezes.

Harvest radishes by hand, pulling up on the green tops at their base near the root top. Leave the green tops on (just removing the dead or yellowed leaves) if bunching or consuming within a few days. Remove the green tops for longer storage.

Wash radishes and place in plastic bags for storage. Ideal storage temperature of 32 degrees F and high humidity (95-100%) will keep salad radishes for 3-4 weeks and daikon radishes for 2-4 months.

Radishes may be preserved by pickling or fermenting into products like kimchee.

Radish is Nutritious and Good for You

Rich in Vitamin C

Important for bones, skin, blood vessels

High in Potassium

Essential for body function, especially the heart, kidney, nerves, bones, and muscles

Good source of dietary fiber

Important for bowel health, lowering cholesterol, controlling blood sugar, and maintaining a healthy weight

Recipes

Common methods of preparing and cooking radish

Video showing how to cut radish

Taste testing ideas: shaved radishes dipped in hummus, coleslaw with radishes, roasted radishes, pickled Daikon radish

Other websites with many radish recipes:

USDA MyPlate Kitchen

SNAP-Ed San Francisco

Tufts Sustainable Farming Project

Sources

• Southeastern Vegetable Extension Workers, 2020 Southeastern U.S. Vegetable Crop Handbook
• LSU AgCenter, Louisiana Vegetable Planting Guide
• UF Extension, Planting Guide
• UF Extension, Vegetable Production Handbook of Florida
• Texas A&M AgriLife Extension, Vegetable Varieties for Central Texas
• Texas A&M AgriLife Extension, Easy Gardening: Radishes
• Texas A&M AgriLife Extension, Commercial Crop Guides: Radishes
• University of Illinois Extension, Watch Your Garden Grow: Radishes
• Alabama A&M & Auburn Universities Extension, Crop Production
• UMass Extension Vegetable Program, Fact Sheets: Radish
• Texas A&M AgriLife Extension, Aggie Horticulture: Asians Eat Giant Radishes
• USDA SNAP-Ed Connection: Radish
• Purdue Extension FoodLink: Radish
• Maynard, Donald N & Hochmuth, George J (2007). Knott’s Handbook for Vegetable Growers (5th edition). John Wiley & Sons, Inc.
• Decoteau, Dennis R (2000). Vegetable Crops. Prentice-Hall, Inc.
• Swiader, John M & Ware, George W (2002). Producing Vegetable Crops (5th edition). Interstate Publishers, Inc.
• Sukprakarn, S, Juntakool, S, Huang, R, and Kalb, T (2005). Saving your own vegetable seeds—a guide for farmers. AVRDC publication number 05-647. AVRDC—The World Vegetable Center, Shanhua, Taiwan. 25 pp.
• Seed Savers Exchange, Seed Saving: A Guide to Isolation Distances
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853