In my experience, onion seedlings don't start bulking up until they start spending some time outside in the sun. I rig up a vented plastic-covered cold frame on the deck and start moving the seedlings out on sunny days as early as possible, but always bring them in at night to avoid chilling. It's pretty dramatic when they change from seedlings to onion-ettes a week or two before transplanting. Your seedlings look good.

Thanks planatus for taking the time to chime in! We've been having some record breaking temps here in NE Kansas recently, so I'll take your advice to heart! I'll need to devise some sort of vented plastic cover for my 6' racks, but I'm sure I can come up with something......

digdirt (Dave) has served as my mentor for seed starting & inspired me to build this elaborate propagation chamber..... LOL Some members said even Red Green would be envious! I'll add you to my short list of mentors!

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I have one of those $60 metal racks from the cathedral of home improvement out on the deck. It has 4 shelves, two of which are adjustable. Using my sewing machine, I've made two covers for it, one from sheet plastic and one from a sheer fabric. When covered with plastic, the shelf becomes a "grow house" for onions and other cool-season plants in early spring. Once those things are in the garden, I change to the fabric cover, which filters wind and sun to the benefit of tomato and pepper seedlings.

In summer, the shelf makes a great curing rack for onions and garlic.

Here's what I'm trying for the clear effect...

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Used two clear shower curtain liners from Wally World. $7.00

I like your idea of having a second cover as well as using the rack for drying. My creative DW is sewing a second cover from Agribon 19 (from my low tunnels).

I envy your wheels! Late in spring, I often have to drop the second to bottom shelf because the tomato seedlings get so big. Also, I live in a windy location, and often tie diagonal lash lines over the front of the plastic cover to keep it secure.

When I initially started propagating, I used several tables to harden off my transplants & would have to carry all those tables in & out of the shop. It's sooo much easier using these racks!

Wind here, is a big problem for my low tunnels as well as my transplants in racks. I've wanted to get my onions back outside, but we're having wind gusts 45-50 mph!