Still have a problem with radishes…
I live in Manitoba, Canada. The weather here is rather cool in May with threats of frost. Last night was an example. I, and 6-7 of my friends, ALL have the same problem with growing radishes. They all sprout well but then the leaves take over. They are lush and green but the root end does nothing. Almost all varieties do that, though we have had some luck with French Breakfast. Most sites on the internet state that radishes are very easy to grow. Obviously, we are doing something wrong! Words of wisdom?
Temperatures cool with threats of frost are generally too cold for most radish to grow.
The soil must be warm enough for germination and they need bright sun for good bulb formation.
Also if the plants are crowded and not thinned out this will inhibit the bulbs from forming. They should be thinned to about 1 inch apart.
If your growing leaves and no bulbs you may have too much Nitrogen in your soil. You can try rotating your crops to a different garden area.
I sometimes sneak in my radish on the edges of my raised beds.
Also if your spring temps are too cold and then the hot summer starts in, you could try planting some radish toward the end of the season as the temps cool down.
I am gardening in zone 4 and have good luck with French Breakfast and Cherry Belle.