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Get Vegetable Starts Ready for the Trip Outdoors


Seed starts sunning indoors before outdoor hardening off.

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. Seed starting takes some work, and is best achieved with grow mats for warmth, grow lights for “sun” and a good seed-starting mix.

This is the best way to pot up seedlings. These are from a community garden, using soil blocks.

Once your seeds sprout, you might have to thin them (using a small pair of scissors to clip the spare plant off just above soil level, not by pulling it up), and might have to pot up the seedling. This involves carefully transplanting the seedling to a bigger container after its first true leaves form. The true leaves form above the first, or seed, leaves and look like mini-versions of a mature plant’s leaf.

Notice the seed leaves (cotyledons) are basic, long and thin compared with the true leaves, with the ridges typical of mature tomato leaves.

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 acclimation 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.

Last year’s seedlings were more than ready for hardening off; the taller plants were starting to hit the grow lights.

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 hardening off seeds 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.

Despite efforts to shelter these tomatoes, the wind tangled the stems a few years ago while hardening off.

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.

Here’s how to harden off your seed starts:

One to two weeks before planting time, place the seedlings in a box if possible for easier movement and stability. Start with the seedlings in a sheltered, shaded area. We often place ours near the house and in the shade of our glass patio table. The first day, leave them out no more than a few hours and check for dryness when you return them to their indoor spot.

Seeds at varying stages, with the ones on the right getting a boost of afternoon sun indoors

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 if possible, bring 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, with several hours in the sun, the starts are ready to spend the night outdoors. They’ll be ready to plant a day or two later.

If you can’t follow a nice, gradual introduction to the outdoors, do your best and boost plant strength with some wind protection, shade or extra warmth at planting time.

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 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.

Planting in containers allows you to continue easing your plants into heat, sun or wind because the containers are easy to move and monitor.

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.

You’ll be rewarded for giving your plants 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!



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