One of my seed catalogues recommends starting onion seedlings 3-5 to a cell, then transplanting each cell unthinned, to grow a clump of plants. Another reference claims that if clumps are spaced about 25% wider than for single plants, bulb sizes won't be much smaller but yield/area (weight) will increase.
Anyone here have relevant experience?
I've usually started my onions in shallow wooden boxes. At transplant time I lift them and soak in a basin if water to disentangle the roots.
Using multi-seed cells and transplanting the groups of seedlings sounds like much less work.