Concur: It is the ground temp that inhibits bulb formation. Sparkler is a beautiful radish, but it is somewhat temperamental.
Radish (Raphanus sativus 'Sparkler White Tip')
Sally: I have not grown that variety, but I do love winter radishes both in salads and cooked dishes. my favorite is the Chinese Red Meat/Watermelon. Mine are baseball size right now.
Radish (Raphanus sativus 'Red Meat') I have also grown the Korean
Daikon Radish (Raphanus sativus 'Tae Baek') and the Japanese. They do best as a fall planting but Watermelon and Minowase will grow in the spring. They have a long DTM ( around two months) are large, but at least in fall plantings have a long harvest window.
Salad radishes are great for salads But they do get pithy fast. When they are ready, they are ready, tomorrow may be too late.
