Image: Kateryna_MA/Shutterstock.comOriginating in China thousands of years ago, radishes spread west via Egypt during the time of the pharaohs, then to Greece, Rome, and other European countries. They found their way to North America in the late 1500s. Radishes are quick-growing and generally require 4 to 10 weeks from seeding to harvest, depending on type. They are most often eaten raw in salads, but are also stir-fried, pickled, or used in soups. Most of the flavor is in the skin and diminishes after peeling.
Types & Varieties Multiple types of radishes exist, with some of the more popular being red or red and white. Varieties include Cherry Belle, Early Scarlet Globe, Red Globe, Champion, Red Prince, Sparkler, Daikon, Black, White Icicle, and California Mammoth White. Daikon radishes, also known as Asian or white radishes, are identified by their slender shape and coloring. They come in a range of colors from white, red, or purple to light green and tend to be larger and milder than other radishes. Within the daikon type are several varieties including Tama Hybrid, Mino Spring Cross, Summer Cross No. 3, Chinese White, Chinese Rose, Celestial, and Tokinashi. Additional cultivars include Icicle Short Top, Alpine, Miyashige, April Cross, and Minowase Summer Cross. A daikon heirloom, watermelon radishes (also known as Chinese radishes) have a white, round, edible root. As its name implies, it resembles a watermelon with reddish-pink flesh encircled by a white rim. Varieties include Red Meat, Shinrimei, Roseheart, and Beauty Heart. Black radishes have a black or dark brown skin with white flesh when peeled. Varieties of black radishes, also known as Spanish black or Erfurter radishes include Long Black Spanish, Round Black Spanish, and Nero Tondo. CULTIVATION Radishes germinate at soil temperatures between 65 and 85°F with good moisture, though new cultivars tolerate hot, longer days. Color will deteriorate when grown on the same land for many years; regular crop rotation can also help avoid soilborne pests and diseases. Rapid growth ensures a mild flavor and crisp texture while slow growth may result in a woody texture and high pungency. Daikon radishes can be planted in the fall; cold weather allows the root to enlarge and enhances taste. Ideally, daikons should be planted in soil with temperatures between 50 to 65°F, but plants can tolerant temperatures as low as 25°F. Upon maturity, daikon radishes will measure up to 18 inches in length, approximately 10 weeks after planting. Watermelon radishes and black radishes also grow best in cooler weather and should be planted in late summer or early fall. Weeds are more problematic for these varieties than daikon radishes and should be removed; watermelon radishes generally reach maturity within 8 weeks and can be harvested as they begin to bulge from the soil. Pests & Diseases Cabbage maggots can be a serious threat, as they burrow into plant roots. Flea beetles chew small holes in leaves, often rendering them unsaleable. Sawflies feed on leaves and shoots but can be tempered by an application of bitter melon. Whiteflies range in color despite their name and harm radishes by feeding on plants and spreading disease. Fungus gnats can help reduce fly populations, as well as sticky traps. Bacterial black spot will develop in storage at warmer temperatures, while black root or black root rot causes misshapen and blackened roots due to bacteria in the soil, and is a serious threat. Root scurf/wire stem occurs when seedlings are attacked by fungus but survive. If the fungus attacks mature radishes, it is called scurf; symptoms are similar to black root. Root rot causes wilting and tissue deterioration, ensuring irrigation water is clean reduces incidence. Radish scab, identified by circular lesions on tissue and roots, renders plants unsaleable. Downy mildew occurs at cool, damp weather, causing yellow spots on leaves and a white cottony growth. Mosaic virus causes mottling and stunts growth but can be counteracted if caught early. Infected plants should be removed.
Storage & Packaging
Optimum storage temperature is 32°F and rapid cooling is essential to shelf life. Radishes are often top-iced with 95 to 100% relative humidity.
Common radishes maintain quality for 7 to 14 days with tops, and 21 to 28 days without.
Daikon and watermelon radishes can be stored under the same conditions; daikons will last several weeks and black radishes can be refrigerated for months in perforated bags.
References: Cornell University, Michigan State University Extension, Ohio State University, Oregon State University, University of California Agriculture & Natural Resources, University of Florida/IFAS Extension, University of Illinois Extension.
GRADES & GOOD ARRIVAL
Grade standards include U.S. No. 1 and Commercial, providing for two styles of radishes, topped and bunched. Topped means radish tops are clipped back to not more than 0.375 inches in length. “Bunched radishes” have full-length tops, tied in bunches.
Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the USDA or CFIA inspection was timely; and (3) the entire lot was inspected.
|U.S. Grade Standards||Days Since Shipment||% of Defects Allowed||Optimum Transit Temp. (°F)|
|10-1||5 4 3 2 1||15-3 14-3 13-2 11-1 10-1||32°|
Radish Retail Pricing: Conventional & Organic