Can You Winter Sow Tomatoes?
Winter sowing works best with herbs, native wildflowers, and cold-loving crops, but you can do it with heat-loving plants like tomatoes! Just because you can doesn’t mean you should; so, is this the best method for sowing tomato seeds? Let’s find out.
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Tomatoes are heat-loving crops that excel in the summer. They appreciate warm, long days with direct sunlight. Their seeds need warm temperatures to germinate, so most gardeners start seeds indoors. Though most people do this, it doesn’t mean it’s what you should do! Experiment with winter sowing to save valuable indoor space.
Winter sowing is a relatively new gardening technique that uses the seasons to your advantage. Instead of sowing seeds indoors in containers, you’ll repurpose old milk jugs into mini-greenhouses. Clear plastic containers and pots with humidity domes also work well instead of milk jugs.
The seedlings sprout outdoors in the containers. They don’t need a hardening-off period, and they’re easy to transplant directly into your garden. Try this method and you’ll grow tough plants for your survivor garden. It’s a cheap, easy way to start seeds, but can you do it with tomatoes?
The Short Answer
Yes, you can winter sow tomato plants! Instead of planting seeds in January or February, you’ll plant them from late March through April. They’ll germinate later than your indoor seedlings, though they’ll quickly supersede them in growth. Their mini-greenhouse coverings protect them from late frosts, hungry critters, and strong winds.
The Long Answer
There are some other things to consider when planting tomato seeds outdoors. Not all seedlings may germinate, harsh frosts may threaten maturing plants, and poor drainage can lead to soggy roots. Set your tomatoes up for success so they thrive with little maintenance during the growing season.
Germination May Be Slow
Gardeners in USDA hardiness zones 1 through 8 often experience late spring frosts that freeze the ground. Frozen soil isn’t conducive to healthy root growth, and it slows seed sprouting. Though milk jugs and other containers offer some frost protection, they won’t protect your plants from harsh frosts.
Most seeds stay dormant until the soil reaches the optimal temperature for germination. When winters are uncharacteristically warm, they sprout early and are at risk of frost damage. That’s why it’s best to sow them later in winter; you’ll avoid early germination.
I sometimes see volunteer tomato seedlings sprout in my raised beds in midsummer. They sprout from last year’s tomatoes that fell to the ground and decomposed. Because of their late germination, they don’t often reach a fruiting size before fall frosts arrive. Winter sowing cheats slow germination by insulating the seeds, promoting sprouting in March, April, and May.
When to Winter Sow Tomatoes
The best time to winter sow tomatoes is from March through early May, depending on your hardiness zone and local climate. You want to time sowing so that it coincides with the last average frost date in your region. If it falls in mid-April, sow seeds in April.
Some gardeners live in frost-free climates, where winter sowing is unnecessary. Others have short but harsh winters where this method proves beneficial. Moderate your planting date to match the month of the last frost and your seedlings will grow well with few issues.
In frost-free climates, sow tomatoes anytime the soil temperature hovers above 60°F (16°C). Plant them in containers with fresh potting soil or directly in the garden.
How to Winter Sow Tomatoes
Though this is a relatively new planting method, many gardeners are using it and experimenting with different techniques. Here’s how to use milk jugs, clear plastic containers, or pots with humidity domes:
Milk Jugs
- Cut jugs in half, leaving the handle side attached.
- Create drainage holes in the bottom. Use a hot glue gun tip to burn holes, or poke them out with a sharp knife.
- Place moist soil inside the jugs, filling them up halfway.
- Plant seeds at the appropriate depth.
- Tape the top half to the bottom half, and remove the cap from the top. This ensures proper airflow and evaporation.
- Place jugs in dappled sunlight or partial shade.
Plastic Containers
- Find clear, plastic containers with lids. Opaque ones won’t work, as seedlings need light to mature.
- Poke holes in the bottom and the lid on top.
- Fill containers halfway with moist soil.
- Plant seeds at their appropriate depth.
- Place the lids back on, and situate the containers under filtered light or partial shade.
Pots and Humidity Domes
- Clean and sterilize last year’s container, and prepare new ones for planting.
- Fill pots with moist soil, then place them in a tray without holes.
- Plant seeds in the pots at the appropriate depth.
- Cover the entire tray with a humidity dome.
- Leave the tray against a wall with indirect light or partial shade.
- Ensure the soil is consistently moist while the seedlings emerge.
Protect Seedlings from Harsh Frosts
Though a late winter planting prevents most damage from spring frosts, it may not work every year! Some years late spring frosts threaten young seedlings with cold temperatures and icy weather. The plants sprout with warmth, then wither as the freezing temperatures penetrate the thin plastic covering.
If your seedlings sprout early while frosts are abundant, you can bring the plants into a protected location for the night and back outside when the sun rises. An unheated garage, enclosed patio, or cool room works well. You want to match ambient outdoor temperatures and avoid excessive heat from indoor heaters.
Tomatoes like light, so place them back outside once the temperature rises again. They’re slightly frost-tolerant in enclosed containers if direct sunlight is abundant during the day.
Best Transplanting Practices
Proper spacing at planting ensures easy transplanting in late spring. Plant three seeds in an individual jug or container, and thin the seedlings so the strongest remains. Tomatoes need two feet of space between each other; most containers are smaller than two feet wide and fit one mature seedling.
Avoid overseeding the containers, as the roots can intertwine and grow between each other. Without thinning, you’ll have to delicately separate the roots during transplanting. Some roots may break off and your plants may suffer! Give them space and they’ll grow well with healthy root systems.
After transplanting, ensure the soil stays consistently moist while the tomatoes mature. They grow best in full sun with six or more hours of direct sunlight. If spring frosts occur after you transplant the seedlings, you’ll want to cover and protect them. Use frost cloth, row cover, or glass jars to cover them during freezing nights.
Key Takeaways
- You can winter sow tomatoes! Give it your best shot, take notes of what went well and what didn’t, and hone in on the process each year.
- Late winter and early spring are the best times to winter sow tomatoes. Avoid doing so in early and midwinter when frost is abundant.
- Optimal varieties for this method are cold-tolerant species from northern regions.
- The main thing to watch for is frost! Protect seeds, seedlings, and plants from freezing temperatures.
