Vegetable Gardening

Starting Tomato Plants from Seeds

A variety like ‘Blue Berries’ may not be available at garden centers, but it can grown from seed.

Growing tomatoes from seed has advantages over purchasing transplants at your local garden center. There is a much larger selection of varieties, especially heirlooms; seeds are considerably less expensive than plants; and it is very rewarding to nurture plants from seed to harvest.

Choosing Varieties

Indeterminate varieties grow very tall and require strong supports.

With so many varieties available, how can we possibly decide? Consider how tomatoes will be eaten. Will they be enjoyed fresh as a snack, on grilled hamburgers, or in salads? Or will they be used in favorite recipes for spaghetti or pizza sauce? Choose from slicing, cherry or paste tomato varieties.

Is there enough room to grow indeterminate varieties that grow six feet or even taller? If space is an issue or plants will grow in containers, select determinate varieties. These grow to a height determined by their genetics and stop, generally around three feet.

There are a number of diseases that affect tomatoes so consider disease-resistance when choosing which variety to grow. Catalogs and seed packets indicate resistance to diseases with initials like F for fusarium, TMV for tomato mosaic virus, and V for verticillium wilt. Catalogs and on-line sources have keys if needed.

Containers – Recycled or Purchased

Any container with drainage holes is appropriate for starting seeds. Tomatoes don’t care what kind of container in which they grow. Anything from egg cartons to recycled yogurt cups can be called into service – just poke holes in the bottoms. Save small pots from the garden center when planting annuals in the spring. Wash them with a solution of water and bleach at a ratio of 10 to 1 before use.

Seed starting pots can also be purchased. Pots made of peat and plastic are readily available. Pots three to four inches wide provide enough room for roots to grow without getting pot-bound.

Correct Soil for Starting Seeds

Fill containers with seed-starting or light soilless potting mix. Young roots easily grow through a mix that is light and fluffy. Peat-based products retain water and keep seeds moist while germinating.

Best Time to Plant Seeds

Determine the correct time to plant by counting back eight weeks from the last frost date. In our area, depending on the source you consult, the average last frost date is mid-May. Starting seeds too early results in leggy growth or plants may outgrow their pots. Resist the urge to plant seeds too soon.

Moisten the potting mix before filling containers, leaving a half inch at the top. Put two or three seeds in each pot to be sure at least one strong plant per pot grows. Barely cover seeds with ¼” of additional potting mix and gently firm. Water the seeds with a spray bottle.

Germination of Tomato Seeds

Tomato seeds germinate best at room temperature, but can be encouraged to germinate faster by setting pots on a heating pad set on low. Mist seeds to keep them moist until they sprout. Germination typically occurs in a week or so.

Containers can be covered with plastic wrap using Popsicle sticks to hold the plastic wrap above sprouting seedlings, the greenhouse top of a seed-starting kit, or put in a plastic bag to increase humidity. As soon as seedlings sprout, remove the covering and move them under lights or to a sunny window.

Care of Tomato Seedlings

New seedlings need at least 12 hours of light every day.

Seedlings need a lot of light – 12 hours minimum – for best growth. Even the sunniest window may have difficulty providing enough light. Seedlings grown under lights are more compact and robust.

Supplemental lights should be placed just a few inches above seedlings so they don’t stretch to reach the light. Move the lights up as plants grow.  If plants are grown near a window, be sure to turn them every day so they don’t lean toward the light.

Water seedlings to keep the soil moist but not soggy. Once they have their second set of true leaves, begin fertilizing with a water-soluble fertilizer at half-strength every two to three weeks.

A small fan blowing across seedlings provides good air circulation, reducing the risk of disease and strengthening stems. In lieu of a fan, rub a hand across the tops of plants several times a day.

If plants get too large for their containers, repot them to larger pots. Being pot-bound stunts their growth.

Hardening Off Tomato Plants

Gradually acclimate tomato plants to the weather conditions outside.

As the last frost date draws near, begin acclimating plants to the outside gradually. Start with a couple hours in a shaded, protected site and slowly increase their exposure to both sun and wind.

Try starting tomato plants from seed this year. It is a great way to garden with me!




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