Radish Seeds - Daikon, Japanese Minowase

How to Plant Daikon Radish Seeds

Daikon radish seeds should be planted in an area with full sun or partial shade with loose, well-draining soil. In preparation for planting, remove any rocks from the soil to ensure strong and even root development and add organic matter such as compost or leaf mulch. 

We typically recommend direct seeding your radishes in the garden. Most root crops, radishes included, do not do well being transplanted. And because they are so quick to mature - starting them inside is unnecessary. Plant your daikon radish seeds directly in the garden about ¼ inch deep and one inch apart. As they germinate, and they typically germinate fairly quickly, thin the seedlings until they are four to six inches apart. 

Like most seeds, daikon radishes need consistent and regular watering in order to germinate effectively. We recommend watering everyday until germination. After germination, daikon radishes will benefit from at least an inch of water per week. 

When to Plant Daikon Radish Seeds

Daikon radishes are a cool weather crop and do best when planted for a spring or fall harvest. In the spring, radish seeds can be planted as soon as the soil is workable - typically four to six weeks before the last frost. In the fall, they can be sown four to six weeks before the first frost. Warmer weather causes radishes to bolt and the roots to become woody and inedible. 

Radishes are extremely frost tolerant and will germinate in temperatures as low as 40 degrees Fahrenheit, this makes them an excellent first crop for the garden. To seed them even earlier, utilize cold frames or row cover to protect tender seedlings from frosts. During this time, and throughout the fall, continuously sow radishes every ten days or so to extend and maximize your harvest. 

Where to Plant Daikon Radish Seeds 

Daikon radish seeds can be planted in a spot with full sun to partial shade. If there is too much shade, your crops may put more work into producing foliage than large, impressive roots. While most radishes can be hidden and snaked in between other crops due to their small size and maturity speed, keep in mind that daikons are quite large - so they may need more space or can be tucked in between crops with more space between them. They will love rich, well-draining soil. Before planting, soil can be amended with plenty of compost and organic matter, especially if you deal with clay soils like we do here in zone seven. We recommend rotating all of your crops. Try to select a location that hasn’t had other radishes in it in the last two to three years. 

How Often to Water Daikon Radish Seeds

As always, it is really important to water regularly and maintain soil dampness from the time you plant a seed until it is a more established plant at which point it is better equipped to handle environmental stress. Not watering enough is the number one reason people struggle with germination and survival of seedlings! 

How to Harvest Daikon Radish Seeds

Harvesting daikon radishes is not complicated but there are some things to keep in mind when pulling up these massive roots. They can be harvested for eating at any stage. The larger they are, the deeper they are, and the more difficult it can be to pull them from the ground - depending on how compacted your soil is. 

These radishes produce hefty foliage so you can typically pull them from the ground with your hand around the crown of the plant. For larger, more mature plants, consider using a digging fork inserted in the soil at least eight inches away from the plant. Lift the soil around the plant, which will loosen the soil and make it easier to pull the radish from the ground. Be sure to harvest all of your radishes before it gets too hot in the spring (when they will bolt) or too cold in the fall (not too many 20 degree nights in a row.)

The species Raphanus sativus is either an annual or biennial depending on the variety. Daikon radishes are biennial, but can be forced to bolt in the first year if the weather gets hot enough, however any seed produced may not be as viable or genetically stable as seed produced in the second year. Radishes are insect pollinated and can easily cross with each other. To grow daikon radishes for seed, we’d recommend having a population size of at least five plants (though between 20 and 80 is typically recommended for large scale genetic preservation). You should note that when growing daikon radishes for seed, the mature spacing distance increases to 12 to 18 inches and staking your plants is recommended as the racemes can reach or exceed four feet in height. This will allow for ample room and airflow around the plants, ensuring healthy seed production. When growing multiple types of Raphanus sativus, it’s recommended to isolate the types by 800 feet to ½ mile. Managing this kind of distance may be difficult but this is mainly important if multiple varieties of Raphanus sativus will be flowering at the same time. 

How to Harvest Daikon Radish Seeds

Harvesting daikon radish seeds, a biennial crop, is done in the second year after the radish has overwintered. Unlike other Brassica crops, though related, radish seed pods do not shatter so they can be left to dry in the field. The pods should be harvested when they turn brown and become brittle. In most growing areas, this will happen in summer. The stalks can be cut down when mature (at least two thirds of the pods are dried). If left for too long in the field, viability can decrease. Once harvested, and depending on maturity, the stalks should be dried for one to five days (until pods are completely dry), either in the sun if the weather allows, or in a protected area. 

Radish seeds do not shatter, so the seeds must be extracted more forcefully than other crops that produce seed similarly. The pods can be placed in a bucket or on a tarp and walked on to crush the fruits, which will separate the seeds from the pods. After this, seeds can be winnowed. Raphanus sativus seeds can be expected to hold their viability for six years if stored under cool, dry conditions in an airtight container.