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Tomatoes

When to Plant

Tomatoes can not be started too early in the ground as they are a tender warm-season crop that can not bear frost. In most regions, the soil is not warm enough to plant tomatoes outdoors until late spring and early summer except in zone 10, where they are a fall and winter crop.

Choosing a Planting Site

  • Select a site with full sun and, ideally, a space where tomatoes (and members of their family, especially eggplants, peppers, and potatoes) have not grown in the previous couple of years. See tips on crop rotation.

  • Dig soil to about 1 foot deep and mix in aged manure and/or compost. Give it two weeks to break down before planting.

How to Plant

Seedlings

  • Due to the long growing season for a warm-weather crop, many gardeners purchase starter tomato plants from a nursery.

  • However, tomatoes can be direct-sown in the garden if the soil is at least 55°F. Note that 70°F soil is optimum for maximum germination within 5 days. Be certain that your grown season is long enough to bring the plants to maturity. See your first fall frost date.

  • Or, you can plant tomatoes by seed indoors for a head start. Sow seeds a 1/2 inch deep in small trays 6 to 8 weeks before the average last spring frost date. See our Planting Calendar for seed-starting dates specific to your area and our article on “Tomatoes From Seed the Easy Way” for more tips.

  • Harden off your own seedlings for a week before transplanting them in the ground. Set them outdoors in the shade for a few hours on the first day. Gradually increase this time each day to include some direct sunlight. Learn more about hardening off seedlings.

Transplanting

  • Transplant your seedlings or nursery-grown plants after all danger of frost has passed and the soil is at least 60°F.

  • Place tomato stakes or cages in the soil at planting. Staking and caging keep developing fruit off the ground (to avoid disease and pests) and also help the plant to stay upright. See instructions on how to build stakes, cages, and tomato supports.

  • When you transplant tomatoes, add a handful of organic tomato fertilizer or bone meal (a good source of phosphorus) to the planting hole.

  • Do NOT apply high nitrogen fertilizers such as those recommended for lawns, as this will promote luxurious foliage but can delay flowering and fruiting. 

  • When planting seedlings, pinch off a few of the lower leaves. Here are two ways to set seedlings in the soil:

  • Place each root ball deep enough such that the bottom leaves are just above the surface of the soil. Roots will grow all along the plant's stem underground. Plant seedlings 2 to 3 feet apart. Crowded plants will not get sufficient sun and the fruit may not ripen.

  • Alternatively, lay long, leggy transplants on their sides in trenches 3 to 4 inches deep. Bury the stems up to the first set of true leaves. Roots will develop along the buried stem. If you plant this way, consider setting four tomato plants in compass-point positions (north, south, east, west). This formation enables you to fertilize and water the plants in the middle.

  • Remember to allow enough space for the plants to spread out.

  • Water well to reduce shock to the roots.

How to Grow

Watering

  • Water in the early morning so that plants have sufficient moisture to make it through a hot day.

  • Water generously the first few days that the tomato seedlings or transplants are in the ground.

  • Then water with about 2 inches (about 1.2 gallons) per square foot per week during the growing season. Deep watering encourages a strong root system.

  • Avoid overhead watering and afternoon watering. Water at the base/soil level of a plant to avoid splashing water on the leaves (which invites disease).

  • Mulch 5 weeks after transplanting to retain moisture, keep soil from splashing the lower leaves, and control weeds. Apply 2 to 4 inches of organic mulch such as straw, hay, or bark chips.

  • To help tomatoes through periods of drought, find some flat rocks and place one next to each plant. The rocks prevent water from evaporating from the soil.

Fertilizing

  • You should have already worked compost into the soil before planting, and added some bonemeal to the planting hole when transplanting.

  • Side-dress plants, applying liquid seaweed or fish emulsion or an organic fertilizer every 2 weeks, starting when tomatoes are about 1 inch in diameter (some folks say "golf ball-size"). If you are using an organic granular formula such as Epson Tomato-Tone (4-7-10 or 3-4-6), pull mulch back a few inches and scratch 2 to 3 tablespoons fertilizer around the drip line of the plant. Water in, and replace mulch.

  • Continue fertilizing tomatoes about every 3 to 4 weeks until frost.

  • Note: Avoid fast-release fertilizers and avoid high-nitrogen fertilizers. As stated, too much nitrogen will result in lush foliage but few flowers and little or no fruit.

Care

  • If growing vining tomatoes, pinch off suckers (new, tiny stems and leaves between branches and the main stem). This aids air circulation and allows more sunlight into the middle of the plant.

  • Gently tie the stems to stakes with rags, nylon stockings, twine, or soft string.

  • As a plant grows, trim the lower leaves from the bottom 12 inches of the stem.

Pests/Diseases

Tomatoes are susceptible to insect pests. To avoid overpopulation of insect pests, try the following.

Tips

  • Monitor tomato plants daily, checking under leaves, checking fruit, and checking near the soil.

  • To dislodge many pests like aphids, spray plants with with a good jet stream from the hose.

  • Handpick insects bigger insects like tomato hornworm with gloves on, dropping into a bucket of soapy water.

  • Apply insecticidal soap directly to the insect on the plant; this works for smaller pests such as aphids and spider mites.

  • Apply horticultural oils or sprays diluted in water. Neem oil sprays block an insect’s air holes.

  • If you choose as a last resort to use insecticides like Sevin, keep in mind that you may be killing beneficial insects as well.

Common Pests

  • Tomato cutworm (early in the season). Indicated by a chewed stem.

  • Aphids will cause yellow curling leaves and white sticky residue.

  • Flea Beetles cause holes in leaves.

  • Tomato Hornworm and tobacco hornworm cause defoliation.

  • Whiteflies indicated by sticky white residue.

  • Leaf miners are indicated by tunnel or zigzag patterns on leaves.

  • Corn earworms (aka tomato fruitworms), stink bugs, and slugs cause holes in fruit.

Common Diseases

  • Blossom-End Rot causes the bottom side of the tomato to develop dark, sunken spots, due to a calcium imbalance. See the link for remedies and prevention.

  • Early Blight is a fungal disease that causes leaves to drop. In July, the risks of blight increase, due to the combination of high humidity and warm days and nights. It starts with dark, concentric spots (brown to black), about 1/2-inch in diameter on the lower leaves and stems. If you catch it early and destroy infected leaves, you plant may survive. The best defense for outdoor tomatoes is good ventilation and stripping off the lower leaves as the fruits develop helps this, as well as helping the ripening tomatoes have maximum exposure to sun. 

  • Late Blight is a fungal disease that causes grey, moldy spots on leaves and fruit which later turn brown. The disease is spread and supported by persistent damp weather. Unfortunately, once your tomato has late blight, there's really no solution. See our blog on "Avoid Blight With the Right Tomato."

  • Mosaic Virus creates distorted leaves and causes young growth to be narrow and twisted, and the leaves become mottled with yellow. Unfortunately, infected plants should be destroyed (but don't put them in your compost pile).

  • Fusarium Wilt starts with yellowing and wilting on one side of the plant and moves up the plant as the fungus spreads. Unfortunately, once this disease strikes, the plant needs to be destroyed.

  • Powdery Mildew is a fungal disease which leaves white spots or a dusting of white on the leaves. It can be managed. See the link to learn more.

  • Cracking: When fruit growth is too rapid, the skin will crack. This usually occurs due to uneven watering or uneven moisture from weather conditions (very rainy periods mixed with dry periods). Keep moisture levels constant with consistent watering and mulching.

How to Harvest

  • Leave tomatoes on the vine as long as possible.

  • Harvest tomatoes when they are firm and very red in color, regardless of size, with perhaps some yellow remaining around the stem. Harvest tomatoes of other colors (orange, yellow, purple, or another rainbow shade) when they turn the correct color.

  • If temperatures start to drop and your tomatoes aren't ripening, use one of these methods:

  • Pull up the entire plant, brush off dirt, remove foliage, and hang the plant upside down in a basement or garage.

  • Place mature, pale green tomatoes stem up, in a paper bag and loosely seal it. Or wrap them in newspaper and place in a cardboard box. Store in a cool (55°F to 70°F), dark place. Cooler temperatures slow ripening; warmth speeds it. Check weekly and remove soft, spotted, diseased, or ripe fruit.

  • Never place tomatoes on a sunny windowsill to ripen; they may rot before they are ripe!

  • Watch this video for tips on how to ripen green tomatoes. 

  • You can harvest seeds from some tomato varieties. Learn how here.