Knowledgebase
When to plant out tomato seedlings #897925
Asked April 20, 2025, 6:55 AM EDT
District of Columbia County District of Columbia
Expert Response
Thanks for reaching out with your question. There are a few things to consider when planting out your tomato seedlings. One of the main considerations is whether you started your seedlings outdoors or indoors.
If you started your seedlings outdoors (like in a greenhouse), they’re likely already acclimated to sun, temperature changes, and maybe even some amount of wind, so it’s safe to plant them out now. Zone 7’s last frost date has passed, and the 10-day forecast looks ideal. Just make sure the plants have strong roots and keep an eye out for unexpected cold or extreme weather. Planting on an overcast day and watering well after transplanting can help reduce stress.
If you started your seedlings indoors, they need to be gradually acclimated to outdoor conditions—a process called hardening off—to prevent sunburn and shock. Start now by placing them outside for an hour in a shady, sheltered spot. Each day, increase their outdoor time by about an hour, slowly introducing more sun and wind over two weeks. This helps them build the strength they need to thrive when transplanted.
One note about watering: during hardening off, tomato seedlings dry out faster because they’re adjusting to sun, wind, and outdoor temps, so check the soil daily. Water them before putting them outside to prevent wilting, but avoid overwatering—aim for lightly moist, not soggy soil. Adjust based on the weather: sunny or windy days need more water, cloudy or rainy days need less. If they wilt a bit in the afternoon but bounce back by evening, that’s normal. Once planted, shift to deep, less frequent watering to encourage strong roots.
I've included a schedule for how you might pace this to acclimate your seedlings.
| Day | Time Outside/Conditions | Notes |
1 | 1 hour in a shady spot | start on a mild day that isn't windy |
2 | 2 hours in shade/partial shade | check to see if leaves are wilting, curling up, or looking splotchy. If you see signs of sunburn, reduce sunlight and |
3 | 3 hours in dappled sunlight | seedlings can be exposed to a gentle breeze at this point |
4 | 3-4 hours in dapples sunlight or partial sun | Protect your seedlings from from strong midday sun. Early morning or late afternoon is best. |
5 | 4-5 hours in partial sun | |
6 | 6 hours in partial sun | Make sure plants are watered before setting out since time outdoors is increasing |
7 | 6-8 hours in full sun (try to avoid strong midday sun--early morning or late afternoon sun is best) | If it's cold or windy, make sure you provide some protection for seedlings |
8 | 8 hours in full sun | This week you begin leaving seedlings out for longer periods of time |
9 | 10 hours in full sun | |
10 | 12 hours in full sun | |
11 | All day--exposure to slightly breezier conditions should be okay at this point | Continue to monitor for sunburn or dehydration |
12 | Overnight (as long as low temps are in the low to mid 50s) | If weather is lower than 50°, you should protect the seedlings |
13 | 24 hours | Seedlings should look strong and ready to plant |
14 | Ready to Transplant (ideally if it's a bit overcast since this will help with transplant shock) | Make sure to water well after planting |
This resource has some additional information about hardening off seedlings: https://extension.illinois.edu/blogs/good-growing/2020-04-06-starting-garden-hardening-indoor-seedlings.
Please reach out if you have additional questions.
Happy gardening!
Rebekah|DC Master Gardener Volunteer
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