The short answer to growing a radish from a radish is no. The edible part of the plant is a storage organ, a taproot, and planting it alone will not yield a new, harvestable radish. To propagate new radishes, the existing plant must be allowed to complete its full life cycle. This process involves encouraging the plant to produce flowers and, subsequently, viable seeds.
Understanding the Radish Plant Cycle
The common garden radish, Raphanus sativus, is generally cultivated as an annual crop, meaning it completes its life cycle within one growing season. The familiar, colorful radish we eat is a swollen taproot. This root holds energy that will be used later for flowering and reproduction. New radishes are grown exclusively from sexual reproduction, meaning they must start from a seed.
Although often harvested in its first year, the radish is botanically classified as a facultative biennial. This means the plant has the genetic potential to require two full growing seasons to produce seeds. In the first season, it develops the root and foliage; the second season is dedicated to flowering and seed set. Gardeners aiming for seeds must manipulate the plant to simulate the conditions that trigger this reproductive phase.
Unlike plants that reproduce vegetatively, such as potatoes or garlic, the radish root lacks the necessary nodes or buds to sprout a new plant. If a mature root is replanted, it may initially sprout leaves using its stored energy, but it will not develop a new taproot suitable for harvest. The stored energy is instead diverted toward the eventual production of a flower stalk.
Encouraging a Radish to Produce Seeds
To obtain seeds, select mature radish plants to remain in the ground after the main harvest. This process requires allowing the plant to “bolt,” meaning it sends up a tall, rigid flower stalk. Bolting is triggered when the plant senses environmental stress or a change in seasonal light and temperature patterns.
Many radish varieties need a period of cold temperatures, known as vernalization, to initiate flowering. The plant must be exposed to temperatures between 32°F and 50°F (0°C to 10°C) for several weeks after the taproot has matured. Following this cold period, the return to warmer temperatures and longer daylight hours signals the time to allocate energy to reproduction.
Once the plant bolts, it quickly develops small, four-petaled flowers. Successful pollination is required for the plant to begin forming the seed vessels. These vessels are small, green, pea-like pods botanically called siliques.
The siliques swell as the seeds inside mature. It is important to leave the pods on the plant until they are completely dry and brittle, indicating the seeds have reached full maturity and are ready for harvest. Harvesting too early will result in non-viable, immature seeds.
Collecting and Saving Radish Seeds
The time for seed collection is when the siliques have fully dried out and turned a light tan or straw color. The pods must be completely brittle and rattle when shaken, which usually occurs late in the season, often several weeks after the flowers have faded. At this stage, the entire flower stalk can be carefully cut from the plant base and moved to a dry, protected area for processing.
The process of extracting the seeds from the dried pods is called threshing. This can be accomplished by gently crushing the brittle pods by hand or by placing them in a bag and lightly rolling over them to break them open. After threshing, the seeds must be separated from the chaff, which are the remaining pod fragments. This separation is often done by winnowing, using a gentle breeze or fan to blow away the lighter debris.
Before long-term storage, the radish seeds must be entirely dry to prevent mold and maintain their viability. Once dried, they should be stored in an airtight container, such as a glass jar or a sealed paper envelope, labeled with the variety and the year of harvest. Stored in a cool, dark, and consistently dry location, radish seeds can remain viable for planting for up to five years.