Growing Tomatoes
from Seed to Harvest

IF you've never bitten into a fragrant, vine-ripened, sun-warmed tomato harvested fresh from your own garden, you haven't tasted a real tomato. And once you do, you'll never again be satisfied with the mealy supermarket imposters. Fortunately, tomato plants are easy to grow and remarkably productive.

Tomatoes are long-season, heat-loving plants that won't tolerate frost, so it's best to set them into the garden as transplants (young plants) after the weather has warmed up in spring. You can purchase tomato transplants, but there's something especially rewarding about starting your own plants indoors. Plus, by growing your own transplants you can choose from among hundreds of tomato varieties that are available as seed but rarely sold as transplants.

Quick to germinate and grow, tomato seeds are best sown indoors about six weeks before your average last frost date. (To determine your last frost date, ask a gardening neighbor or call your Cooperative Extension office.)

Here's what you'll need to start tomato seeds indoors:

There are hundreds of tomato varieties available as seed, and choosing a few for your home garden can be a daunting task. Here are a few things to consider:

  • Decide on the type of tomatoes you want; for example, cherry tomatoes, slicers or tomatoes for making sauce or paste.
  • Consider the size of the mature plants. "Determinate" tomatoes grow to about 3 feet tall and are the best choice for containers. "Indeterminate" tomatoes get very large, up to 6 feet tall. (All tomatoes benefit from support, such as Tomato Cages or Tomato Ladders.)
  • Look for disease-resistance. Tomatoes are susceptible to a number of diseases that may or may not be a problem in your region. To be on the safe side, I always grow at least one variety with resistance to verticillium and fusarium (designated by a V or F after the variety name).

For more detailed information, read How to Select the Right Tomato Variety.

Seedstarting Mix
Always use a sterile, soilless mix to start seeds. Avoid garden soil, which often drains poorly and may harbor disease organisms. Look for mixes labeled for seedstarting, such as our Germinating Mix; it has a fine texture that's perfect for delicate seedlings. (Learn more: Choosing the Right Soil for Seedstarting.)

Tomato seedlings in APS

Tomato seedlings in a self-watering APS seedstarter.

You can start your seeds in just about anything that holds soil and has drainage holes — I've used small yogurt containers and even egg cartons with holes poked in the bottoms and waterproof saucers underneath. However, I've found it more convenient to use purchased pots, such as Biodegradable Cowpots and seedstarting systems, such as the GrowEase Seed Starter Kit.

Warmth and Light
Seeds germinate best at warm room temperature (70-75 degrees F); you can speed germination by providing bottom heat with a heat mat. Once they're up and growing, seedlings grow best in cool room temperature, about 65 degrees F.

Although you can start your tomatoes on a sunny windowsill, you'll get better results growing them under some type of grow light. Winter and early spring sunlight isn't nearly as intense as summer sunlight, and there are fewer hours of daylight, too. Insufficient light can lead to weak, spindly plants. A light garden with adjustable fluorescent lights is ideal for seedstarting. Learn more: Gardening Under Lights.

Step-By-Step Seedstarting

Here are the steps to successfully starting your tomato seeds.

  • Thoroughly moisten the seedstarting mix, and then fill the containers to within 1/2" of the top. Firm the mix but don't compact it.
  • Place two or three seeds into each small container or each cell of a seed starter. Cover the seed with about 1/4" of soil and gently firm it over the seeds.
  • Water to ensure good seed-to-mix contact. You can use a plant mister or just dribble a stream of water over the top. You don't need to soak the soil, just moisten the top layer.
  • Place the pots in a warm spot or on top of a heat mat. At this point, the seeds don't need light.
  • Keep the mix moist but not soaking wet. If your seed-starting system has a greenhouse top, use it to help hold moisture. Or, you can lay some plastic kitchen wrap over the tops of the pots.
  • Check pots daily. As soon as you see sprouts remove the covering and place the pots in the sunny window or under grow lights, keeping the lights just an inch or two above the tops of the plants.

Growing On

Continue to keep the soil moist but not saturated. Dry seedstarting mix is lighter in color than moist mix — a good indication that it needs water. Some gardeners run a fan in the room with their growing seedlings; good air circulation reduces the chances of disease problems, such as damping off.

If you're growing plants on a windowsill, rotate pots daily so plants grow upright instead of leaning toward the light. If you're growing under lights, raise the lights as the plants grow, keeping them just a few inches above the plants.

Thinning out tomato seedlings

Use a scissors to thin out crowded seedlings.

Thinning. For the strongest, healthiest plants you'll want just one seedling per pot or cell. Thinning (removing extra seedlings) is a tough task for many gardeners who hesitate to dispatch the seedlings they've been nurturing. But it has to be done. Select the strongest, healthiest seedling and use a pair of scissors to snip off the others at the soil line. You can try to transplant the extras into different pots, but you risk disturbing the roots of the remaining plant and, realistically, how many tomato plants can your garden accommodate?

Fertilizing. Once the second set of true leaves appears, it's time to begin fertilizing. The first two leaves are called "seed leaves;" subsequent leaves are called "true leaves." Use a soluble fertilizer, such as PHC for Seedlings, diluted to half the recommended rate. Apply it once or twice a week.

Repotting.Your tomatoes may need to be transplanted to larger containers if they outgrow their pots before it's time to set them outdoors. Don't allow the plant to get pot-bound, with the roots filling the container, or growth may be stunted. For step-by-step instructions, read How to Repot a Tomato Seedling.

Transplanting into the garden. Wait to transplant your tomato seedlings into the garden until after the average last spring frost date. Be prepared to protect the seedlings with garden fabric (row cover) if a late frost threatens. If all goes well, you'll be harvesting ripe tomatoes in eight weeks or less.

Sow tomato seeds indoors six weeks before your last frost date. Begin by moistening a sterile seed starting mix, such as our [a href="" target="_blank"]Germinating Mix[/a]. Don't use garden soil, which often drains poorly and may harbor disease organisms. Add mix to the containers. Here, we're using our [a href="" target="_blank"]GrowEase Seed Starter[/a]. Gently firm the mix to remove air pockets. Use your finger or a pencil to poke two holes per cell, each about 1/4" deep. Planting two seeds per cell increases the likelihood that at least one seed per cell will germinate. Shake some seeds into your hand … … and place one seed in each hole. Sprinkle additional mix over the cells to fill the holes and cover the seeds. Once again, gently firm the mix to eliminate air pockets, and then water lightly to ensure good seed-to-mix contact. Use a plant mister or apply a few drops of water to each cell. Place the tray in a warm place, about 70 to 75 degrees F. At this point you don't need to worry about providing light. Covering the tray helps retain moisture, which is important for germination. Check daily, taking care to keep the planting mix moist but not saturated. Once you see the first sprout, place the seedlings under grow lights, keeping the lights a few inches above the tops of the plants. Remove the greenhouse cover so air can circulate around the seedlings. This helps prevent disease problems. Keep the planting mix moist but not soggy. A self-watering seed starter makes it easy. You fill the reservoir and it delivers water to the roots when they need it. When the seedlings are about 2″ tall, it's time to thin. Choose the strongest, healthiest-looking seedling in each cell and remove the others by snipping them off at the soil line. Once the seedlings have two sets of leaves, it's time to start fertilizing. Once a week, apply a soluble fertilizer, such as [a href="" target="_blank"]Easy Grow Fertilizer[/a]. About a month after sowing, gently remove one of the seedlings and look at the roots. When the roots begin to fill the cell, it's time to repot. Each seedling gets its own container — in this case, a 4" [a href="" target="_blank"]Self-Watering Transplant Pot[/a]. Fill the pot with moist planting mix. Unlike other types of seedlings, it's OK to bury the stem of a tomato plant — in fact, it's a good idea, because the plant will grow roots along the buried stem. Water the planting mix, and then place the seedlings back under the grow lights for a few more weeks of growth. This seedling was transplanted into a 4" [a href="" target="_blank"]Cowpot[/a]. These biodegradable pots can be planted right in the garden. Once all danger of frost has passed, it's time to transplant your seedlings into the garden. If your seedlings are more than about a foot tall, it's best to plant them in a trench so you can bury the lower part of the stem. Begin by pinching off the lower branches and leaves. You want to avoid burying any of the foliage to prevent rot. Begin by digging a trench about 8″ deep and 6″ wide. If your tomato plant is in a biodegradable Cowpot you can plant it pot and all. Otherwise, gently remove the plant from its pot. Lay the plant on its side in the trench. Gently bend the stem so the top portion is above the soil line. Fill in the trench, firming the soil around the stem so it's upright. Water thoroughly and add a support. Here, we're using a [a href="" target="_blank"]Tomato Cage[/a]. Be prepared to protect the seedlings with a row cover, such as [a href="" target="_blank"]GardenQuilt[/a], if a late cold spell threatens. Keep the plants watered and fertilized, and you'll be harvesting ripe tomatoes in about two months.

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