Hardening off young tender plants so they can withstand the heat, wind, rain and cold is the most important thing you can do for your young plants. For me, it is also the most difficult because I grow so many and it is hard to give them the individual attention they would love. If you only have a few plants, the process goes like this:
- depending on the weather, start exposing your seedlings to the outdoors around 3-4 weeks after they have germinated and have at least one set of leaves beyond their seed leaves (seed leaves are those skinny smooth leaves that come up first at germination and generally fall off after the plant has matured a bit);
- on their first day outdoors, go slow and cool. Do NOT put them out in direct sunlight on their first day out and do NOT put them out on a windy day. Direct sun or wind (warm or cold wind) will do them in. Ideally you would have a shady spot with dappled sunlight and you would put them out for a few hours in this spot (morning or afternoon is fine as long as the spot is semi-shady and the weather is still;
- make sure they are watered before you put them out. The weather is harsh on these young seedlings and they need to be babied for a few days;
- it helps if you open a door and let cool air and breeze into the growing room before you take them out (not absolutely necessary, but it helps);
- Bring them back in after a few hours. There is no set time here, as it depends entirely on what the weather is like that day, how far along your seedlings are, and what their inside growing conditions have been. Just check them every hour or so and if they are looking sad or wilted, bring them back in;
- Repeat these steps for a few days, gradually giving them more sun and more time outside;
- It usually takes about 7-10 days to get the tomato and pepper seedlings fully hardened off. If you do it gradually and add more sun to the hardening off area each day, they should be able to take full sun, rain and gentle winds after this. Hail and strong cold winds will probably damage your plants, no matter how careful you have been in hardening them off.
A Few Other Things of Note:
- Plants are often stronger than you think, so don’t completely despair if something goes wrong. I have had my tomato seedlings decimated in hailstorms, put them aside to compost them, and then be amazed to see them come back stronger and greener than before (no guarantees, but don’t be too quick to toss them);
- If your plants are exposed to sun too early or for too long they may get sunburned and look more of a pale yellow rather than a dark lush green. They are OK. Just look at the new growth and if it looks good, your sunburned leaves will not affect your plant or your tomatoes;
- Don’t keep your seedlings on the ground if they are out for any length of time. Rabbits and mice love the tender growth and will be quick to eat them while you’re away.
- If the weather is bad for a good part of the spring and you can’t get your seedlings into the ground, do two things: 1) pot them up into larger pots so the roots will keep growing until the weather clears, and 2) fertilize them with some kind of nitrogen-rich foliar spray (seaweed, fish emulsion or something like that).
That’s all for now. I will try and come back to add more later. Please comment with any questions and I’ll be happy to try and answer. Thanks!