A Complete Guide to Growing Tomatoes from Seed Indoors
Whether you want a head start on the gardening season or live in an area with a short growing season, starting tomato seeds indoors is a great way to get an earlier harvest. In this article, I’ll cover everything you need to know to successfully grow tomatoes from seed inside your home.
When to Start Seeds
The ideal time to start tomato seeds indoors varies depending on your location’s average last frost date. As a general rule, start seeds 6-8 weeks before the last expected frost in spring. From my experience gardening in Zone 6, I usually start my tomatoes in late February or early March to have plants ready to transplant outside around mid-May.
You’ll want to check your local agricultural extension office for the exact frost date information for your area. Starting too early runs the risk of leggy, unhealthy plants. But starting too late means your tomatoes won’t have enough time to fruit before fall. Proper timing is important.
Choose the Right Seeds
When selecting tomato varieties, consider factors like your climate, soil conditions, desired use (sauce, slicing, etc.), and growth habit (determinate vs. indeterminate). Heirloom varieties tend to have the best flavor but may have lower disease resistance. Hybrids often have greater yields but won’t “true to seed” if you save them.
Be sure to select varieties suited for growing indoors as well. Bushy, compact types like ‘Tumbling Tom’ and ‘Window Box Roma’ work well in limited space. Avoid tall, vining varieties meant for garden stakes. Read seed packets for plant height details.
Prepare the Growing Media
You’ll need a light, well-draining soil mix to start tomato seeds. Peat pots are convenient but can dry out quickly. Cell packs or seed starting trays with individual cells work well too. I like the reusable plastic seedling trays.
For soil, a standard seed starting mix will suffice. You can also make your own by combining equal parts perlite or vermiculite with potting soil to improve drainage. The key is to avoid dense, water-retaining potting soils meant for houseplants. Seedlings’ tiny roots need oxygen.
Sowing the Seeds
Fill your containers three-quarters full with prepared seed starting mix. Firm it down gently but don’t compact it. Sprinkle seeds evenly across the surface at the recommended spacing for the variety. Individual cell packs are idea for tomatoes.
Cover seeds with a thin layer of additional mix, around 1⁄8 to 1⁄4 inch deep. Firm again and water gently from below until fully moistened. Place lids or plastic wrap on trays to keep humidity high until seeds sprout. Avoid standing water.
Germination and Care
Keep seeds warm at 70-80°F for best germination, which usually takes 7-10 days for tomatoes. Once sprouted, remove lids and move to a sunny window or under grow lights for 14-16 hours per day. Maintain a soil temperature of 65-75°F.
Use care when watering seedlings to avoid disturbing tender roots. Water from below until soil is moist but not soggy. Monitor moisture levels and allow the top inch to dry slightly between waterings. Rotate trays weekly to prevent stretching.
After the first true leaves appear, a diluted liquid fertilizer can be applied every other watering. Continue grow lights and heating until night temperatures stay above 50°F for indoor-started plants. Gradually harden them off before transplanting.
Transplanting to Larger Containers
Once seedlings have 2-4 true leaves, it’s time to transplant up to roomier pots. I wait until tomato plants are 6-8 inches tall before moving outdoors to maximize production. Pick a warm, overcast day for minimal shock.
Gently remove seedlings from cells or trays and tease any circling roots outward. Place them in 4-inch pots with good potting mix amended with compost or other organic material. Water thoroughly to settle soil.
To prevent soil from falling away, I pinched the bottom of peat pots when transplanting. This worked better than peeling away the multiple bottom layers as damage could occur. The biodegradable pots slowly broke down over time in larger containers.
Keep new transplants in partial sun for a week, then gradually move to full sun. Maintain warm temperatures and keep moist until well established. Fertilize monthly with an all-purpose formula as plants grow. Monitor carefully for pests or other issues.
Transplanting Tomatoes Outside
Wait for nights reliably above 50°F before permanently moving tomatoes outdoors, usually around mid-spring. Hardened off plants can tolerate cooler evenings down to 45°F. Follow these transplanting tips for a smooth transition:
- Pick an overcast day or evening for relocation to minimize shock.
- Plant tomatoes in a hole twice as wide as the root ball and an inch deeper than previous pot.
- Water thoroughly after nestling plants in loose, fertile soil amended with compost.
- Consider using tomato cages or stakes at planting to train vertical growth.
- Protect tender transplants from sudden sun or wind with mini hot caps the first week.
As long as nights remain warm, tomatoes can be started directly in the garden at the same time using seedlings as spacing markers. Just be sure to supply good support as they grow. Regular care and suitable conditions will yield delicious homegrown tomatoes for summer!
Dealing with Common Issues
No matter how carefully you start tomatoes from seed, some problems may still arise. Here are solutions to a few frequent indoor tomato seedling troubles:
Leggy Growth: Too little light causes etiolated, spindly stems. Provide grow lights within 4 inches of tops for 14+ hours. Rotate daily.
Damping Off Disease: Fungal issue in moist, crowded conditions. Improve airflow, drainage, and spacing. Water only when dry.
Spider Mites: Tiny pests thrive indoors. Spray with water or neem oil. Wipe leaves weekly until hardening off.
Pests: Aphids, fungus gnats – spray plants, use yellow sticky traps near pots, remove weeds/debris hiding pests.
With patience and proper care, most seed-starting issues are easy to overcome. With luck, soon you’ll be enjoying a bounty of homegrown tomatoes! Let me know if you have any other questions.
Steps for Growing Tomatoes from Seed Indoors
| Step | Details |
|---|---|
| 1. | Choose a container and growing medium. Pots or starter trays work well. |
| 2. | Fill the container 3/4 full with seed starting mix or potting soil. |
| 3. | Read your seed packet for planting depth. Lightly cover seeds with soil 1-2 times their diameter. |
| 4. | Water the soil lightly and place the container in a warm spot with indirect sunlight. |
| 5. | Keep the soil lightly moist. Check daily and water as needed. |
| 6. | When seedlings emerge, move them to a spot with morning sun and afternoon shade. |
| 7. | Transplant to larger pots or the garden once they have developed their 2nd set of true leaves. |
FAQ
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When should I start tomatoes from seed?
You can basically start tomato seeds indoors 6-8 weeks before the last expected frost date. This usually works out to be in late January or February for most areas. Starting them earlier than that isn’t necessary. I’d say late winter or early spring is your best bet.
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What kind of soil and container should I use?
A seed starting mix is your best option for soil. It’s light and well draining so it won’t compact down. As for containers, you can use small pots, old take out containers, or plastic egg cartons. However, plastic cups work well and are kind of cheap. Go for something 2-4 inches deep. Your seeds don’t need a lot of room at first.
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How far apart should I plant the seeds?
You’ll want to space them about 1/4 to 1/2 inch apart, and no more than 1/2 inch deep. Tomato seeds are small, so err on the side of more shallow. At the same time, they need some coverage. Maybe ask a gardening friend for advice if you’re unsure. Usually about 1/4 inch works well depth wise in my experience.
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How do I know when to transplant them?
Look for the first set of real leaves to form after the seed leaves. This usually happens within 7-10 days. The leaves will be wider than the seed leaves. You can transplant when they are 2-4 inches tall. Don’t wait too long or they will become root bound in their small containers. Transplanting sooner than later is best here.
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How far apart should the transplanted seedlings go outside?
For regular size tomato plants, space them about 24-48 inches apart in the garden bed. Different varieties may need more or less room. I’d say a good rule of thumb is 2-3 feet between each plant. Staking or caging them will help save space if needed. But leaving at least a couple feet between gives the plants room to grow nicely without overcrowding each other.
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When is it safe to plant them outside?
You can plant tomato seedlings outside after the last expected frost date for your area. However, it’s always a good idea to harden them off first before putting them in the ground. Over about a week, acclimate them to the outdoors for increasing periods each day. Wait for nights that don’t dip below 50 degrees F. Tomatoes don’t like cold weather! Usually late spring is perfect timing outside, like May in many areas. But check your forecast to be safe.
