How to grow tomatoes from seed
Seed catalogs are brimming with varieties of tomatoes, many more than you’ll find as seedlings this spring at local nurseries and garden centers. Growing tomatoes from seed requires a bit more work, but with minimal investment, you’ll have healthy seedlings ready to transplant on Memorial Day.
For starters, you will need a warm location for seed germination and a bright spot for the seedlings. You’ll also need water, soluble fertilizer, containers, a tray with a cover and labels. A sterile, lightweight potting mix is optimal for seed starting and decreases the incidence of disease. Do not use garden soil to start tomatoes.
Containers should be about 2 inches deep and have adequate drainage. Repurposed yogurt cups or take-out containers will work as long as you make holes in the bottom for drainage. Reduce the chance of disease by sterilizing the containers. Soak them for 10 minutes in a bleach solution of one part bleach to 10 parts water and allow to dry thoroughly.
Cell packs are the way I usually go. They come in many sizes and fit well in seed trays that come with raised, clear plastic lids. Being frugal, I often reuse cell packs from year to year, sterilizing them after use. Peat pots and expandable peat pellets are also a good investment because they allow direct planting of seedlings into the garden.
Seed packets contain critical information, including when to start the seeds indoors and when to transplant outdoors. In Allegheny County, tomatoes should be seeded 5-8 weeks before transplanting — early to mid-April to allow for planting on Memorial Day. If started too early, seedlings become weak and leggy.
Also note the recommended depth of planting (¼ inch for tomatoes), temperature for germination (75-85 degrees) and the days to germination (7-10 days). Seed packets detail days to harvest, the time between planting outdoors and your first ripe tomato, as well as suggested spacing in the garden. Most tomatoes require 2-3 feet depending on cultivar and staking method. All tomatoes require full sun, at least six hours a day.
Before planting seeds, dampening the soilless potting mix. Fill the containers with the wet mix and gently tamp down. Place the seeds, cover with ¼ inch of dampened mix and water gently. I generally plant two seeds in each container. If both emerge, I eliminate the weakest one by cutting it off at the soil line. Be sure to label your seeds. You can purchase labels or repurpose plastic utensil handles, aluminum blinds, cut-up plastic milk jugs or Popsicle sticks.
Place the containers in a tray and cover to retain moisture. If you aren’t using lids that come with seed flats, plastic wrap can be used or the whole tray can be placed in a clear plastic bag. The labels will keep the plastic above the soil, allowing space for the seedlings to grow.
Place your trays in a warm location. Tomatoes germinate best at 75-85 degrees. I place my trays on covered radiators; others use the top of the refrigerator. You can also purchase a germination mat for this specific purpose.
Cotyledons, which are tiny leaves, should sprout in a week or so. Once they have emerged, uncover the trays and place them in a warm spot (70 degrees) under very bright light. A south- or west-facing window will work, but fluorescent shop lights produce steady light and sturdy plants. My lights are suspended with adjustable chains above a table from the joists in my basement. The lights, containing two cool bulbs, are adjusted for the next several weeks to be 2-4 inches above the seedlings and are kept on via timer for 14-16 hours a day.
Keep the seedlings consistently moist as they grow. Feed them with half-strength soluble fertilizer every two weeks.
A week or so before planting out in the garden, gradually acclimate your stocky seedlings to the harshness of the outdoors. Reduce water, place them first in a warm, shady spot outside and eventually transition to full sun.
Seeds for tomatoes are viable, on average, for five years. Extra seeds can be stored from year to year in an airtight container in a cool dry place.
Spend the coming weeks choosing from the dizzying array of tomato choices online or in seed catalogs. It’s fun to try a few new ones each season to discover some new favorites.
This article was first published in the Pittsburgh Post-Gazette on February 16, 2018