Radishes belong to the Brassica family and are one of the most common garden vegetables, widely cultivated throughout the world.
They vary in colour and shape from red, white, purple or black and can be round or long and cylindrical.
Like other members of the Brassica family they contain sulforaphane and indole-3 which are thought to be protective against cancer when eaten raw. They are also contain a significant amount of vitamin C, and are a good source of folate, fiber, riboflavin, and potassium, as well as good amounts of copper, vitamin B6, magnesium, manganese, and calcium.
This humble vegetable has many health benefits and being so easy to grow, makes it a good vegetable to include in your garden patch.
Growth habits and planting needs
Although radishes will grow in all types of soil they prefer a friable soil that is light and fertile. The root system of the mature plant extend most thickly down 15 to 20 cm from the surface and so it is important that the soil be well dug to this depth and enriched with well rotted compost and be free from stones. The tap root grows beyond this but moisture is needed at this shallower depth where the majority of the root system lies. The site should be sunny to encourage the growth of the tubers.
This diagram from Root Development of Vegetable Crops by John E. Weaver and William E. Bruner shows the root development (grid in ft) under optimal conditions. It also shows the importance of keeping weeds away to prevent competition with surface roots.
Even though radishes can be cultivated closely, being well spaced allows the root system to develop properly and for the radish tubers to grow well and give good yields.
Radishes prefer a soil within the range of pH 5.8 to 6.8. It is most important that the soil is friable.
Radishes need potassium but not so much nitrogen so as a crop they should follow fruit in the crop rotation system . Fruit crops deplete nitrogen left from earlier crop rotations. Too much nitrogen leads to leaf growth with smaller tubers.
Sow seeds 1 cm deep, thinning to 5 cm apart (15 cm for larger varieties) in a sunny location in well prepared soil. Use the thinned leaves in salads. If plants are shaded by other plants, leaves will grow bigger at the expense of the tubers. Mature plants will grow to have a spread of 15 -22 cm and a height of 15 to 45 cm.
Seedlings will emerge in about 4- 5 days from sowing. Keep sowing more 8 to 10 days later to ensure continuous cropping over the growing season.
It is important to keep the plants well mulched and weed free so that the shallow root system will not be disturbed by cultivating. To develop good sized radishes moisture should be plentiful and consistent.
The radishes should be ready to harvest in 5-7 weeks. Carefully easy the radishes from the ground and cut the leaves leaving a couple of cm of the stems.
Wash the radishes well, removing the roots and slice them into your salads.