RedJim, once pulled, mild radishes will stay that way unless you wet the slices and dust them, mix with “wasabi” powder (horseradish)!
Radishes fall into two categories: spring and winter. Now is the time to plant fall radishes, because if you plant those in the spring, they’ll flower and not make a big root. Chinese radishes start out very spicy and get milder in storage. These include Beauty Heart (watermelon), Green Luobo, China Rose and others.
If you want a radish with a kick, that’s planted summer-fall, it’s hard to find one more zippy than Black Spanish. Plant to harvest about frost time. There are long and round types; the round varieties store better. Most winter radishes keep in the fridge until about May! They also tend to be much larger than spring radishes. Here’s Chinese Green Luobo I grew a few years back, followed by Beauty Heart.
Most winter radishes are ready about two months after planting and will take mild frost. Harvest as the tops die down and the roots get large, 2 1/2-4 inches across.