That should be fine as long as you keep them well watered. usually, after planting my onion plants in spring I shove all the excess (probably 50-60 at least) into a 5 inch deep, 32 inch long planter on approx. 1 inch centers and let them go. Then I just harvest every other one during the growing season and i end up with a bunch of 1 inch pearl onions that work great for pickling.

Thanks Makalu! I'll give it a try then.