This is a reminder I’ve made over the last couple of years around this time.
If you are new to gardening, and have started plants indoors under lights, don’t forget to harden them off before moving them outside or they will probably die!
Hardening off simply means to introduce them slowly to the outdoor weather, usually over the course of about a week. Otherwise the shock of moving from a sheltered room and grow lights to outdoors will just be too much for the plants.
I harden off my plants according to the following schedule of outdoor time:
Day 1: 15 minutes
Day 2: 30 minutes
Day 3: 1 hour
Day 4: 2 hours
Day 5: 4 hours
Day 6: 8 hours
Day 7: Plants are ready to be left outdoors
These times are approximate! Don’t drive yourself crazy over them.
While hardening the plants, you should also introduce them slowly to full sun.
Many people have other ways or systems of hardening plants. For example some people make use of a coldframe or greenhouse and slowly let in more outside air. Other people have different times for different days. Some people make use of plastic milk jugs. As long as it takes at least a week, and you are introducing your plants gradually to the outdoors, it should work fine.
A lot of people ask me questions like what about moving plants from a polytunnel or some other in between situation? I don’t really know. I suggest, if you have a plant you can afford to lose if necessay, set it out for an hour while carefully watching it for signs of stress. Look at the plant again the following day. If there are no signs of stress, than it is probably okay to just set the plants outdoors. To be certain, it’s still better to harden them first.
Hardening off plants is a risky time! Many gardeners lose plants while trying to harden them. Watch your plants closely, and if any start showing signs of stress, move them back inside for a few days and try hardening them again from the beginning.
If you move your plants back indoors after hardening, you will need to reharden them!
