When and How to Plant Out Your Winter-Sown Seedlings: 7 Pro Tips
Winter sowing is all the rage, and for good reason! It’s an easy, efficient way to start seeds without grow lights or heat mats. But what do you do when the seedlings mature? Seasoned grower Jerad Bryant shares seven pro tips for planting them out in the garden.
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Winter sowing involves placing seeds in insulated containers, like milk jugs, outdoors. The seeds germinate at the optimal time when the seasons shift from winter to spring. As outdoor temperatures rise and the days lengthen, the sprouts readily mature into seedlings ready for transplanting.
As your seedlings mature, you’ll wonder how and when best to plant them out into the garden. They may have intertwining roots that tangle up in the soil. You’ll take them out, separate them, and prepare them for their new homes. This process is relatively straightforward—if you’ve never winter-sown seeds, I recommend trying it with a flat of veggies or herbs this year!
Your winter-sown crops will mature quickly, providing you with prolific harvests sooner than indoor-started transplants would. Without further ado, here are seven expert tips for when to plant out seedlings.
Let the Seedlings Mature
Young plants don’t transplant well—their small roots and stems are subject to breakage, pests, and diseases. You may waste time moving them early, only to find they’ve withered or broken a few days after transplanting.
The first step is waiting for the plants to fully mature. You’ll see the tiny plants mature into young specimens with robust leaves and stems. A good rule of thumb is to wait until they have three or four true leaves above their seed leaves, or cotyledons. The cotyledons look different than the true leaves; they’re the first to appear, and they’re smaller than the others.
Cold-loving crops and wildflowers mature in late winter, while other heat-loving species may take longer to reach a good size. Practice patience during this time; a good way to wait is to plant more seeds, as you can never have too many!
Open the Containers
As the plants mature, they’ll reach the tops of their containers. You may see leaves or stems pressing against the lids. This is a sign that it’s time to remove the lids and let the plants bask in the outdoor weather. This process acts as a hardening-off period, where the seedlings grow used to the outdoor conditions.
Though you’ll remove the lids and let the plants harden off, you’ll want to keep the lids nearby. Late spring frosts may still occur, and they’ll threaten your growing crops. Place the lids back on the containers on nights you expect harsh frosts or strong winds.
Another key consideration is strong sunlight. In early spring, you may receive unexpected sunshine and warmth for a few days before cold weather returns. Ensure the plants have dappled sunlight on extremely hot winter or spring days to avoid sunburn and scald marks.
Wait for the Last Average Frost Date
Your region’s last average frost date is the best indicator of when to plant out your seedlings, whether vegetables, wildflowers, or herbs. Some plants like growing after the date, while others prefer maturing before the date. Move them at the right time so they excel with little care or maintenance.
Cole crops like broccoli, cabbage, and cauliflower are frost and cold-tolerant. You may transplant mature seedlings two to four weeks before your last frost date. They’ll grow well under cool, moist spring conditions.
Other species like tomatoes, eggplants, and peppers are frost-tender; their growth will stagnate under cool weather. Keep them warm and protected in their containers until a week or two after your final frost date.
Most herbs, veggies, and wildflowers transplant best in the weeks after your final frost. The lengthening days, rising temperatures, and ample sunshine create the perfect conditions for rapid spring growth.
Slide Plants Out
Now comes the fun part! It’s time to remove the growing seedlings from their containers for planting out into the garden. The easiest way is to press from the bottom drainage hole or wiggle the edges. You can also cut off one side of the container and slide the seedlings out. Their tangled root mass should pop out easily.
Some growers may want to save their containers for next year; in that case, don’t cut the side panels. Leave them whole, and gently tip the vessels on their sides. With light tapping and easing, you should be able to lift the soil up and out.
Avoid picking them out by their leaf tips, as this can lead to the stems snapping off the roots. Grasp the seedlings by their lower stem portions and slowly ease them out of their containers. Now that the plants are out of their old homes, you can easily inspect their roots and separate them further.
Separate the Seedlings
How to separate the seedlings depends on how they grow. Native plants often grow in clumps where many seeds fell to the ground in the last year. The strongest specimens survive and thrive, while the weakest succumb to natural pressures. Separate native species into clumps, then transfer the clumps to the garden.
Veggies, herbs, and woody perennials grow better with ample space from other specimens. You’ll want to gently tease them apart, ensuring each plant has a well-developed root system. Though care is key to not breaking the roots, a little roughness is okay. Winter-sown crops are hardy and resilient; they’ll rebound in no time!
While separating the specimens, consistent moisture is key. You don’t want those tender root fragments drying before you can plant the crops in the ground. Keep them in the shade, and moisten their root zone with misters to maintain sufficient moisture levels.
Prepare the Site
Proper preparation helps your crops take off once they establish themselves in your garden. You want the site to have rich, fertile, and well-drained soil. Avoid transplanting into soggy or excessively sandy sites with low moisture content.
Prepare the site by digging holes for each of the transplants. You want the holes to be as deep and twice as wide as the plants’ root balls. Avoid amending the holes with any products, as that can lead to bound roots rather than healthy ones.
When you amend a hole with compost or potting soil, it creates a cushy home for the roots. They’ll stay within the amended portion and struggle to extend into your garden’s native soil. The best time to amend is ahead of planting; add compost or a similar mulch a few months before transplanting and rake it in. Don’t worry if you forget, as you can amend the area after planting.
Transplant Seedlings
Place the seedlings in their holes, cover the roots with soil, and water the site well. They may sit still for a few days while they adapt, and you’ll see new growth shortly after they establish themselves. They need plenty of sun, consistent moisture, and regular airflow to thrive.
After planting out your seedlings, careful monitoring ensures your crops perform their best during the growing season. Watch for late frosts that can harm your tender specimens, and cover them on cold nights. Row cover, frost cloth, or greenhouse plastic work well as temporary insulators.
The other consideration is the soil! Soil health is where plant health starts; healthy soil grows healthy plants. After planting, amend the site with a two to three-inch thick layer of compost, leaf mold, or a similar organic mulch. It’ll decay and feed the ground with nutrients while it insulates and covers the roots, trapping moisture where they need it most.
And that’s all there is to it! With care, tenderness, and attention to detail, you can safely move your growing species from their tiny containers to your garden beds, containers, or borders.
