Radishes are probably the easiest and fastest garden vegetable to grow. The most common variety of radish goes from seed to harvest in only 3 - 4 weeks!
How to grow radishes
Radishes germinate quickly, usually within 3 - 7 days, under ideal conditions. Radishes prefer a soil pH of 6.5 - 7.0 and loose soil. Keeping the soil moist will speed germination and initial growth, but too much water can cause root rot. For smaller taproots, seeds should be planted 1 cm deep, while larger radishes require a planting depth of 4 cm. Plants should be thinned to 4 - 8 inches apart, in rows 8 - 12 inches wide. To maintain a constant supply of radishes, you can plant new seeds every few days. This is called succession planting.
Radishes can be harvested when the taproot has reached a desired size or the plant can be allowed to go to seed for its edible seed pods, called siliquae. In each case, timeliness determines taste and texture. Roots and seed pods that are too old will be tough and bitter. Radishes can also be grown as a cover crop to add nutrients and prevent erosion, or as a forage crop, to feed livestock.
Because radishes grow so quickly, there are very few pests or diseases to worry about. Flea beetles may chew holes in young leaves, the swede midge (Contarinia nasturtii) may damage foliage or growing tips, and the cabbage root fly larvae may infest the taproot. In each case, good sanitation and keeping the plants healthy are the best defense. Radishes and other cole crops should not be planted in the same location more than once every 3 - 4 years to prevent the spread of disease. Regular crop rotation often breaks up the factors that make up what is called the Disease Triangle.
Radishes as companion plants
Radishes are often planted along with corn, squash and cucumber, which provide welcome shade. Radishes are said to repel cucumber beetles, squash bugs and squash vine borers, but I don't know if that is true. If nothing else, planting radishes makes efficient use of the soil around these larger plants. Some sources claim that radishes repel tomato hornworms, ants, and aphids, but I could find no scientific research to verify these claims.
You can grow a surprising amount of food in your own yard. Ask me how!