How to prepare plants to move to greenhouse from indoors?

Question

I've been growing some starts in this little hot-house thing I made after seeing something similar at a local gardening store. It seems to work great - with a heating pad under one of the flats it's warm, humid and plants grow like crazy.

Now I'm planning to move them outside into a greenhouse I just built. @Ecnerwal mentioned in a previous post that I need to "transition" the plants, but I'm not sure exactly what that means.

When I look up instructions for hardening off plants, they seem to be preparing plants for being put in the ground. Most instructions talk about going from ~30 min outside in light shade to a full day over the course of 7-14 days (not very specific, really), and to cut back on watering.

I'm hoping to have them in the greenhouse for 3-5 more weeks (depending on the plant) at temperatures between 40°F at night and 80-85 max during the day. I expect to be watering them regularly and hoping for them to get pretty big & stocky.

I'm wondering if someone could suggest (in detail, ideally) a good process for going from indoors to outdoors? Thanks!

Answer 1

Principle is basically the same; gradual acclimation to different conditions. In your case the different conditions are the greenhouse, not "outside" (or at least not yet) but otherwise the process is similar - move the plants into the greenhouse for a short period, possibly with some artificial shade at first, or taking advantage of a time when the greenhouse is in partial shade, if that happens.

If you care to get fussy, say 30 minutes on day 1, 1 hour on day 2, 2 hours on day 3, 4 hours on day 4, 8 hours on day 5, 16 hours on day 6 and leave them there on day 7, as one option for a schedule. For a longer schedule, you could make the increment more like 150% time rather than double-time from day to day [30, 45, 1:08, 1:41, 2:20...) I freely admit to not being so regimented about it, but I start moving my plants out when the conditions outside are favorable, and increase their time outside gradually, without getting overly clock-watchy about it. I do watch the plants fairly closely for any signs of distress.

Since you'll be watering you can keep doing that, but you may want to cut back a bit just because they will use a bit less when they are colder.

If your GH temperature is going to 85F you might want a bit more ventilation - most places run vents full-open when the temperature exceeds 70F.