Is the process of hardening off still the same if the plants have sat under grow lights since germination, or can they be put under the sun straight away?
And is there a difference if they have been under heat producing lights?
2 Answers
I grow under lights and with a heat source and I have an approximately one-week hardening off sequence:
- Day 1 - Full Shade on the north side of a building. Out of the wind, if possible.
- Day 2 - Dappled shade
- Day 3 - About an hour of sun
- Day 4 - Morning sun; maybe 3 hours
- Day 5 - Same as Day 4
- Day 6 - Morning sun until roughly noon
- Day 7 - Full sun
Now, if I'm hardening off plants that I'll be putting in full shade, then I'll plant them after Day 2; if they're going into part shade, I'll plant them late in Day 4 or Day 5; and if they're going into full sun, I'll plant them on or after Day 7.
This may seem like an excess of caution, but I've been burnt (pun intended) too many times by planting in full sun too soon. Additionally, some plants are more sensitive to burning, I think, than others - particularly cucurbits, so it's important to take it slowly with them.
If you ask me it depends on how valuable your young plants are. If you have much more seedlings that you need, then you can afford some attrition and the plants that come out of the harsh experience should be hardier than the previous generation and make for a better plant the next year