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Tomato Seed Starting Tips

Tomato seedlings
Tomato seedlings
Tomato seedlings

Tomatoes are a tender, warm-weather crop. Start tomatoes indoors 10 to 8 weeks before the last expected frost in spring. Set tomato seedlings into the garden after all danger of frost is past.

There are more than 1,000 varieties of tomatoes—most are red, others are pink-orange, yellow, purple, brown, whitish-green, or striped.

Best tips on How to Grow Tomatoes.

Small tomatoes are commonly called cherry tomatoes; large tomatoes are called beef or beefsteak tomatoes; egg-shaped tomatoes are called paste or jam tomatoes. Choose tomatoes to grow according to how you plan to use them: cherry tomatoes for salads and garnish, beefsteak tomatoes for slicing, paste tomatoes for sauces.

Some tomatoes grow to bush size—these are called determinates. Others sprawl or grow as vines—these are called indeterminates. Tomatoes that are neither busing nor vining are called semi-determinates.

Tomatoes mature in 50 to 90 days from the time they are transplanted. Tomatoes are commonly transplanted about 40 to 60 days after seed sowing. That means even the quickest maturing tomato variety requires about 90 days to reach maturity from sowing.

Tomato Sowing and Planting Tips

  • Grow tomatoes from seeds or seedlings.
  • Seed is viable for 4 years.
  • Tomatoes are commonly started indoors in a greenhouse or in a warm, well-lit sunroom or kitchen.
  • Sow tomatoes 10 to 7 weeks before you intend to set plants out into the garden.
  • Sow tomatoes in individual pots with a light potting mix.
  • Sow 3 to 4 seeds to a pot then clip away the weaker seedlings once the strongest seedling is about 2 inches (5 cm) tall.
  • Sow seed ½ inch (13 mm) deep.
  • Germination soil temperature can range between 65-86°F (18-30°C); the optimum soil temperature for germinating seed is 86°F (30°C).
  • Germination takes 5 to 7 days at 75°F (24°C) or warmer.
  • Keep seed starting mix just moist until seeds germinate.
  • Tomato seed can be sown directly in the garden if the soil temperature is warm enough—and there are enough days in the season for plants to reach maturity.
  • Seeds are commonly started indoors so that seedlings can go into the garden when the outdoor soil temperature is at least 55°F (13°C) and the nighttime air temperatures is consistently 50°F (10°C) or warmer; plants will not thrive and should be protected if the air temperature is any cooler.
  • Do not transplant seedlings into the garden until all danger of frost has passed unless the plants will be protected under a plastic tunnel or cloche.
  • Seedlings started indoors should be kept under grow light or in a sunny window after germination to ensure bushy growth.
  • Water to keep the seed starting mix from drying.
  • Fertilize with fish emulsion or a soluble complete fertilizer at half strength.
  • Transfer seedlings to a larger container once they are 2 to 4 inches (5-10 cm) tall; be sure that seedlings have sufficient room for root growth. This process is called “potting up”; continue to pot up seedlings as they outgrow containers—until they are transplanted into the garden or a very large container.
  • Transplant tomatoes into medium rich garden soil 12-24 inches (30-60 cm) apart for determinate varieties; 24-46 (30-90 cm) apart for indeterminate varieties.
  • Add aged compost to planting beds in advance of transplanting.
  • Tomatoes prefer a soil pH range of 5.5 to 6.8.
  • Grow tomatoes in full sun for best yield.
  • If you plant seedlings started by another grower, select plant 6 to 8 weeks old; usually in a 4-inch (10 cm) pot. Check the bottom of the pot to be sure roots are not growing through and the plant is not root-bound.
  • When transplanting tomato seedlings, bury all but 2 inches (5 cm) of the plant; first clip away leaves and branches below the top set or two of leaves—new roots will grow from the buried stem.
  • Avoid planting tomatoes where potatoes, peppers, or eggplants have grown recently.
  • Fertilize with an organic fertilizer such as fish emulsion at half strength.
  • Common tomato pest enemies include aphids, leafhoppers, cabbage loopers, Colorado potato beetles, cucumber beetles, flea beetles, tomato hornworms, whitefies, and others.
  • Common diseases include damping off, early blight, late blight, fusarium wilt, bacterial spot and wilt, sunscald, tobacco mosaic, verticillium wilt, mosaic virus.

Interplanting: Plant tomatoes with bush beans, chives, cucumbers, lettuce, marigolds, and peppers.

Container Growing Tomatoes: Choose a container large enough for the type of tomato you are growing; indeterminate tomatoes require at least a 15-gallon container, larger would be better. Determinate tomatoes that can grow in slightly smaller containers.

Tomato Planting Calendar

  • 8-6 weeks before the last frost in spring: start seed indoors for transplanting to the garden in 6 to 8 weeks.
  • 2-1 weeks before the last frost in spring: transplant seedlings to the garden under a plastic tunnel or begin to harden off seedlings; minimum soil temperature is 50°
  • After the last frost in spring, set transplants into the garden; protect plants from chilly nights or cold weather with a cloche or by wrapping spun poly row covers around the tomato cage.
tomato seedlings for transplanting
Tomato seedlings are ready for transplanting to the garden after about 8 weeks.

Types and Classifications of Tomatoes

There are several tomato types and classifications to choose from and grow. Here are some basics:

Tomato growth form or habit:

  • Determinate bush types grow to a predetermined size and then stop—about 3 feet tall; fruits ripen all at once.
  • Indeterminate vine-like plants can grow easily to 6 feet tall or taller; fruits ripen over an extended period—usually until the plant is killed by frost.
  • Semi-determinate types grow taller than determinates but smaller than indeterminates; fruits ripen over and extended period.

Common types and names of tomatoes: There are more than 1,000 varieties of tomatoes; here is a short guide of types commonly grown:

  • Beefsteaks are large, slightly elliptical-shaped fruits; commonly used for slicing.
  • Cherry are small fruits about 1 inch (2.5 cm) in diameter, usually red or yellow-gold colored.
  • Grape-type is elliptical, egg- or pear-shaped about the size of a grape.
  • Paste types are small, oval, thick-meated fruits used for making paste or in cooking.
  • Pear types are small cherry tomatoes that are egg- or pear-shaped.
  • Plum types are also called Italian plum or Roma tomatoes; they are elongated usually 2-4 inches long.
  • Heirlooms can vary in size and appearance; these are varieties that have been in cultivation since before the late 1940s before the first hybrids were introduced. Seeds from heirlooms can be saved and will grow true.
  • Hybrids are first-generation varieties from controlled parent lines; seed from these tomatoes will not grow true.
  • Open-pollinated are tomatoes whose seeds can be saved and will grow true to the parent—unlike hybrids.

Botanical Name: Lycopersicom esculentum

Tomatoes are a member of the Solanaceae family, other members of this family are peppers, eggplants, and potatoes.

More tips: How to Grow Tomatoes.

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    • Saving seeds from favorite tomatoes and other vegetables and passing them on to a family member and friends is a great way to keep favorite varieties growing for future generations and to encourage new gardeners.

  1. Thank you for your information. I have 2 tomatoes one looks like a Tom Thumb/small tomatoes. The other one is a firmer bigger shaped tomato seems to bend slightly in middle. I bought them at a market. With no name attached “silly me”. Now wondering when they will ripen. They both have quite a number of tomatoes indifferent stages of development. Grown in large pots.

    • You can ask the produce manager at the market if she knows what variety of tomatoes they sell; she can check with the grower or shipper. You can also take one or two tomatoes to the farmers’ market and ask one of the farmers if she can identify the tomato. Standard-sized tomatoes take 20 to 30 days from blossom set to reach full size–commonly called “mature green”; they take another 20 to 30 days to ripen, that is begin to change color. A tomato can be picked when it begins to change color–from green to red, pink, yellow, or orange depending upon the variety.

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