When to transfer seedlings

Hi!
(NY, Zone 5 or 6 depending who you ask)
I have some echinacea seedlings that I planted in early March ranging from 1-2 inches high with 3 to 4 leaves. I wanted to free up space under my grow lights, and was wondering if I could transplant them outdoors if I covered them at night or if they tolorate light frost. I don't mind keeping them inside for another month or so, but I thought I'd do no harm in asking.

Thanks!

--Audrey

Doug says they should be transplanted into individual pots when they get 4 true leaves (the leaves that come after the two initial leaves) and grown in their own pot. They should then be hardened off (out for longer and longer times during the day) when it's not overly cold and there's no danger of frost. After a week or so of this - they can be left outside.

When you can leave them outside and the roots are coming to the side of the pot - they can be easily transplanted into their garden position.

That's the optimum way to do it.

You can put the seedling tray outdoors during the day - but out of wind etc and harden it off gradually so you don't burn or set back the seedlings. Not optimum but they'll take cold weather after a week or so of hardening off. They may not grow as quickly as their indoor brethren but if properly hardened off - they'll take a goodly amount of cold (not a really hard freeze)

The key is to harden them off properly and slowly. Doing that is the basic "trick" here.