Growing food from seed is rewarding and less expensive than buying starts. It’s also a way to control the growing medium and ensure healthy plants and use of organic methods. Of course, if you prefer to buy starter vegetables or herbs, the same rules apply: Get your young plants to acclimate to wind, sun and outdoor temperatures before planting them.
These really young seedlings are delicate.
As your plants grow and appear to form solid stems, they are nearly ready to harden off. Hardening off is a way to acclimate the plants. If you go outside on a chilly spring day, you’re cold at first, and then warm up the longer you stay outside. Plants need the same kind of help to ensure they grow strongly and don’t react to abrupt changes in temperature, air movement and sun exposure. Just transplanting to a new location is a shock, so all you can do to strengthen the starts helps.
I realize in some parts of the Southwest, cold is not a problem. Still, your seedlings might have been on heat mats and used to the consistent temperatures in your home, garage or from the mats. Few Southwest gardens have nice, even temperatures from morning through evening or from one day to the next!
Temperature is only part of the acclimation. Wind and sun also affect tender starts. Try to avoid setting new plants outside when winds are high (I know, this can rule out many spring days!). If you can set them out early in the morning, you’ll likely have gentler breezes and less intense sun.
Those of us at high altitude know the sun is more intense in general. It’s also stronger from noon through mid-afternoon. If you can, gradually expose your plants to more intense sun and heat of the day, and cooler evening temperatures. We just place ours in mostly shade the first day, and move them a little each day.
Give Starts a Good Start
Although nursery stock usually is hardier, you can apply some of the same principles to store-bought vegetables and ornamental plants. If they’ve been in conditions similar to your planting location, then go ahead and plant them as soon as you get home. I know you want to. But if a plant has been in a greenhouse and you want to place it in full sun and wind, harden it off a day or two in its new conditions or help it get started with a little shade or wind protection. Then, water, watch them grow and enjoy!
Place your own starts in a box if possible for easier movement and stability. About one to two weeks before planting, start placing them outdoors in a sheltered, shaded area. The first day, leave them out no more than a few hours and check for dryness when you return them to their indoor spot.
Repeat the sheltered exposure each day for several days, gradually extending the time they’re out. After leaving seeds out for most of the day, move them into more sun and wind exposure, starting with a few hours again. Keep alternating sun and shade, gradually increasing sun. Eventually, after a full day outdoors, the starts are ready to spend the night outdoors. They’ll be ready to plant a day or two later.
It’s not always possible to spend this much time moving plants – if you’re at work, for example. Just watch the sun/shade patterns in a protected spot of your yard, deck or patio and place the starts out in the morning. If you’ve estimated correctly, the shade will reach them in a few hours. Gradually place them further out each day to where they will get more sun and less of the shadow. Our problem usually is wind – we have never been able to repeat this process daily.
Don’t feel your crops will fail or you have to start over if you forget to harden off one day or have to skip a day because of weather. Just keep giving them a gradual transition until time to plant. And if worried, add a little extra protection from wind and sun immediately after planting.