Juliarugula way way way lower on tuber production than plants started in ground.   Like, several have had no salvageable tubers other than the mother.
I had this exact experience last year; finding only mother tubers plus a mess of long plump roots, or nothing mother even - just root balls. The only difference was that I didn’t start a single tuber early in pots. I grew almost exclusively in grow bags last season and summed it up to nutrition, and some late planting.
I was really frustrated so I’m glad you started this thread. I’m curious! I planted in-ground this year, and on-time, and am anxious to see what my tuber production looks like. For my most coveted varieties this year, I cut the plants back aggressively, early, hoping to encourage tuber development?
I’ll get a soil test next year and have been considering applying potash in August, if we’re low enough in potassium that it makes sense. Hoping for more ideas from others here to prevent this in the future. It’s such a let down at dig time, so I’m glad to hear you haven’t gotten to any favorites yet!