It will definitely be a challenge, even more so if the current roots are extensive and/or well developed.

The problem has 2 parts:
1. The plants need to grow roots adapted to solid media.
2. In the meantime, the current water-adapted roots will die.

Jean, thanks. So far they're doing fine. Keeping the fingers crossed!

I haven't tried kale because I directly sow it.

A lot of things Hydroponically Grown, like most herbs and tomatoes transplant to potting soil very well.

I have never tried going directly in to garden soil. Potting soil is loose and the roots can adjust, maybe?

Maybe potting them first, for a few days would work? Just a guess!

The plants are being sold in produce department for eating. As "baby kale" I suppose. The leave are about 3-4" long and 2 - 21/2" wide. The same seller usually has several types of herbs and garlic that are hydroponically grown in a greenhouse.

So far they seem to be doing just fine, and that surprises me. I've kept them watered and have put superthrive or fish emulsion in the water a couple of times. They'll stay in the pots until I know they have new roots, then will go into the garden, and they'll have to survive a hot, steamy summer. I've never seen this variety of kale before and don't know how large it will get.