Someone else may have better answers than me about your amendments, but some of my things did benefit from a day or two outside the greenhouse in the sun before disturbing by planting. It may depend on the plant. Plants grow so fast in the greenhouse where its really hot, so when you put them in the ground they just seem to stop and it takes a couple of weeks before I notice any new growth at all (especially if they were in a fertile potting soil like Miracle Gro and they went to a less fertile soil). I'd try a little fertilizer to see if it helps with the yellowing. And by shrivel, you mean a crispy shrivel, or a wilting shrivel? Crispy would be too dry, but if they're wilting, maybe they are just taking the move hard and putting a chair or something over them to keep them in the shade for a day or two might help.

hello Ulma:I would go to a garden center and purchase 2 sixpacts of lettuce; try hardening them off-(see:t&m website factsheet on hardening off..As suggested by the poster above...a chair(lawn chair secured with weed fabric(pins,perhaps))might be a useful aid...
If the lettuce responds in the same way,I would deduce that your soil is off...
goodluck

Uma, yes you should harden off plants coming from a greenhouse outside. Light intensity, cooler weather, and wind can all be a bit shocking to plants if not given the chance to get used to it. To harden plants off coming out of a greenhouse I would do pretty much the same thing as plants coming out of a house. Put them in a nice shady place with morning sun and gradually increase light over a few days, protect them at night depending on what the inside of your greenhouse is set at and let them get some natural breezes but protect from strong winds. A week or so of this kind of treatment should help out your plants. I would only suggest using organic fertilizers like compost and fish emulsions during and right after transplanting to avoid burning your seedlings. You can even try using half strength until your plants get established.

I hope this helps and good luck

Since it is an unknown garden, have you had the soil tested?

No I haven't had the soil tested yet although I did my own pH test in one bed and it was 6 to 6.5. Thanks for everyone's input.