Everything You Need to Know About Growing Tomatoes!

Growing Tomatoes (or any Vegetable) from Seed
How to Grow Tomatoes

Start tomato seeds indoors 4 to 6 weeks before average last spring frost, which is April 15th here in St. Louis. Transplant them out when the soil temperature is ideally 70 - 90 degrees, generally in mid May. The time to start those tomato seeds here in St. Louis is late March.

(The proper time for sowing seeds depends upon when plants may normally be moved outdoors. The periods range from 4 to 14 weeks, depending upon the speed the seedlings grow and the conditions in your home. Check the back of the seed packets to determine when to start your seeds for planting times. Some seeds should be started inside, while others such as lettuce and spinach should be planted directly into the garden.)

  1. Containers
    Use shallow, sterile containers with drainage such as 4 packs or 6 packs.
  2. Seed Starting Mix 
    Use a lightweight, sterile seed starting mix, which is lighter than regular potting mix and allows for the ideal air-to-moisture ratio. Fill the containers three quarters of the way full.
  3. Sowing Seeds
    Place two to three seeds on top of the soil and sprinkle more of the potting mixture lightly on top to cover the seeds.
  4. Moisture
    Once you have planted the seeds, use a mister or hand sprayer to water the seeds, but do not drench the soil.
  5. Germination
    Cover the seed trays with clear plastic wrap or clear plastic dome covers, which are helpful in the germination process. Place the containers in a warm location; near a furnace, on top of a radiator or on top of a special heating mat, to help with germination process.
  6. Sprouts
    The seeds should start to sprout within 2 to 14 days. Once they have sprouted, remove the plastic cover and continue to water with a mister or sprayer or start watering lightly from the bottom.
  7. Light
    Provide as much sunlight or artificial light as possible. It is recommended that grow light be within two to three inches of the foliage and set for 18 hours on and six hours off. If using natural light on a window sill, mirrors and aluminum foil can be used to intensify the gloomy winter sun. An unobstructed southwest exposure is the best.
  8. Water
    Check the soil everyday and continue to mist/spray the soil or lightly water from the bottom. A water soluble, balanced fertilizer can be added when the first true leaves begin to appear. Do not let the soil dry out or let the seedlings wilt. Keep the soil moist, but not soggy.
  9. Air Movement
    Once your seedlings are a couple of inches tall, set up an oscillating fan close by. Fans provide good air circulation and help produce stronger stems and stockier seedlings.
  10. Transplant Seedlings
    When the soil dries out too quickly or the roots have reached the drainage holes, it is time to transplant the seedlings into larger, 3" or 4” containers. Biodegradable peat or paperboard pots are the ideal as they can be planted directly into the garden.
  11. Harden Off Plants
    Seedlings grown indoors always need to be hardened-off before they are planted in the garden by slowly exposing them to outdoor temperatures and sunlight. To harden-off seedlings grown indoors under lights, take them outside and set in dappled sunlight and sheltered from the wind. Gradually acclimate the plants to sunlight by moving them to a sunnier spot after a couple of days. The following schedule, starts with four hours a day and ends two weeks later with a full day. (See schedule below)
  12. Transplanting and Supporting/Staking
    When transplanting tomato seedlings outside, plant them deeply, burying the stem leaving 1-2 sets of leaves above ground. The buried part of the stem will sprout roots and develop a strong, extensive root system. Place any stakes, cages, or other type of supports in the ground just after transplanting to avoid root damage. Space your tomato plants 24-40” apart in the garden to help airflow, enable light and help to prevent disease.
  13. Growing Temperature
    The ideal temperatures for tomatoes to set fruit is between 55°F to 75°F at night. When the temperatures at night in the summer are above 75°F at night, this may inhibit fruit set and can cause blossom drop (no fruit production).
  14. Water
    Tomatoes need about 1-2" of water per week, depending on the type of soil they are growing in. 1 or 2 deep soakings per week in mild weather, and 2 or 3 per week in hot weather should be sufficient. If tomatoes are cracking, back off on the water. Too much water can burst tomatoes and water down the flavor.
Hardening Off Schedule
Days Hours
1 – 4
2 4
3 – 4.5
4 – 4.5
5 – 5
6 – 5
7 – 5.5
8 – 5.5
9 – 6
10 – 6.5
11 – 7
12 – 7.5
13 – 8

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When to Buy and Plant Purchased Tomato Plants

If you are planning on buying tomato plants, the advice given by horticulturists and gardeners alike in the St. Louis area is to buy the varieties you like, when they are made available at the nurseries, and keep them indoors until the middle of May.


Tomato Types

Tomatoes are grouped into two main types according to growth habit and production.

Determinate types grow in a compact, bush form, requiring little or no staking. Fruit is produced on the ends of the branches; most of the crop ripens at the same time. One or more successive plantings will ensure an extended harvest period. Determinate types are often the choice of those who want a large supply of ripe fruit at once for canning. Staking is generally not needed.

Indeterminate varieties continue to grow and produce fruit all season until first frost. Tomatoes in all stages of development may be on the plants at one time. The plants set fruit clusters along a vining stem, which grows vigorously and long. Under optimum conditions, some can grow over 15', but in most home gardens they generally reach about 6'. Some indeterminates have a bush form with stockier vines, which set fruit clusters closer together. Staking is definitely needed for indeterminate varieties.

In between these two types are the Semi-Determinate. The plants will grow larger than determinate varieties, but not as large as indeterminate. They produce a main crop that ripens at once, but also continue to produce up until frost. Staking is recommended.

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Tomato Disease

You will see various letters or string of letters (A, F, N, V, T and or St) on seed catalogs or packages that denote the disease resistance of the plant. The following are the most common diseases that affect tomato plants and how to avoid or treat them.


Early Blight or Alternaria Stem Canker (A)
The fungus Alternaria solani, which is present wherever tomatoes or potatoes are grown, causing early blight. Prevalent throughout the United States, the fungus overwinters on tomato plant debris. Spores can then spread to tomatoes in spring via wind or splashing rain, but they need wet leaf surfaces to germinate and grow. Low leaves that drip with dew each morning provide perfect conditions for early blight.

When tomato plants begin to set their fruit, brown spots will develop on the lowest leaves of the infected plants. As the spots expand and become more numerous, the leaf tissues between the spots may turn yellow before the leaf eventually withers. The spots will have outer rings around a bull’s-eye center.In most cases, early blight damage will be limited to the bottom third of a tomato plant, where they tend to be more damp. The plants still may manage to yield a good crop, if treated or pruned.

Watering tomatoes in the morning allows the leaves to dry out during the day. If this is not possible, water the plants at the base and try to not get the foliage wet. Planting tomatoes in different locations (plant rotation) is a good idea, assuring the new plants are not planted with the disease carrying spores.

When you see the first early blight leaf spots, use pruning shears to clip off all leaves within 12 to 18 inches of the ground, removing no more than 20 percent of the plant’s total leaf mass. An organic fungicide applied at first site, may help to keep the fungus under control.

(Other diseases or wilts will also produce spots and yellowing, but the spots will not have the rings around them as on Early Blight.)

Fusarium Wilt (F, F1, F2 or F3)
Fusarium wilt is a soil fungus that is present when the daytime temperatures are 80 degrees and above for many consecutive days. Once the fungi enters the plant through the roots, it will multiply in the plant’s vascular system, the leaves on individual stems to show symptoms first. The infected plants tend to grow normally until they begin to set fruit. At that point, leaves on some stems will start to yellow and wilt severely in midday sun. As the disease progresses, more stems and leaves will yellow and wilt, until the plants eventually collapse and die. Plant tomatoes in different locations for up to four years will help prevent this disease

Nematodes (N)
Plant parasitic nematodes, are small microscopic roundworms which live in the soil and attack the roots of plants. Yield reductions can be extensive but vary significantly between plant and nematode species. In addition to the direct crop damage caused by nematodes, many of these species have also been shown to predispose plants to infection by fungal or bacterial pathogens or to transmit virus diseases, which contributes to additional yield reductions. Rotating crops and growing resistant varieties can help prevent problems. Keep beds weeded, as many weeds serve as nematode hosts. Planting French marigolds with tomatoes can help reduce the nematode numbers.

Verticillium Wilt (V)
Verticillium wilt symptoms on tomatoes are similar to those of Fusarium wilt. Often no symptoms are seen until the plant is bearing heavily or a dry period occurs. The bottom leaves become pale, then tips and edges die and leaves finally die and drop off. V-shaped lesions at leaf tips are typical of Verticillium wilt of tomato. Infected plants usually survive the season but are somewhat stunted and both yields and fruits may be small depending on severity of attack. To combat verticillium wilt, grow any of the widely available resistant varieties, and rotate plantings so you’re not growing in the same soil more than once every four years. Plants that show only mild symptoms can sometimes be nursed through the season with mulch and regular watering.

Tobacco Mosaic Virus (T)
The foliage shows mosaic (mottled) areas with alternating yellowish and dark green areas. Leaves are sometimes fern-like in appearance and sharply pointed. Infections of young plants reduce fruit set and occasionally cause blemishes and distortions of the fruit. The dark green areas of the mottle often appear thicker and somewhat elevated giving the leaves a blister-like appearance.

St=Stemphylium Grey Leaf Spot
The disease is limited to the leaf blades. The fungus infects plants from the earliest seedling stage to maturity. Initial symptoms include one to several minute brownish black specks that appear on both surfaces of the leaf. The area changes in color from brownish black to grayish brown, as the spots enlarge and these centers crack and partially drop out to give the leaf a shot-hole appearance. The entire leaf then turns yellow, droops, and eventually dies.

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