This came up in another
thread but I thought it deserved one of its own.
It's a pretty simple idea and I've seen it work really well for transplanting potted plants into the ground, and works especially well when moving plants from one part of a garden to another (eg. thinning plants growing too close in rows). I've seen some pretty good transplant rates from thinnings of squash, kohlrabi, strawberries and cucumbers.
Basically all you do is cover the transplant for a few days (usually 2-3) and then remove it. It may require more time in warmer climates than mine. Once you see the plant either start to lean to one side, produce new growth, or turn yellow, its time to take the cover off. Its probably best to do so in the early morning, late evening, or during a cloudy/rainy day.
Make sure to use a light coloured cover. Something that will reflect sun rather than absorb it. Black and dark green, even light green coloured pots either fried my plants, or at least did much more poorly than buckets and plant pots white or beige. I've tried using clear pop bottles but that just fried my transplants.
I've also found it best to use something that is big
enough so that plant leaves aren't touching the cover. In my
experience, the ones that are touching there covers don't do as well.
It may be beneficial to 'ween' them off the pot so-to-speak, so that instead of removing it for good, you take it off for only a few hours one day, and increase a few hours every day until you've reached a full sun cycle. I'm too lazy/busy to be that technical about it but I do monitor my transplants for a few days after I remove its cover if the weather is warm and sunny, as it can make them wilt severely, and sometimes die. In these cases I put the cover on during the peak sunny times in the middle of the day and take it off in the early evening.