Tomatoes (scientific name Solanum lycopersicum) are members of the nightshade (Solanaceae) family. Other members of this family are chili, including Bell pepper, eggplant, petunia, potato, tobacco, and tomatillo.
Tomato tags have a sequence of capital letters after the variety name such as VFNTA. Each letter stands for resistance to a different disease or pest. V = verticillium wilt, F = Fusarium wilt, N = nematodes, T = tobacco mosaic virus, A = alternaria stem rot canker. Heirloom varieties tend to have less disease resistance.
Heat and Sun Tolerance
The pollen of most tomato plants becomes sterile at 90° F and tomato production often ceases during hot periods. Pollen of some varieties, however, remains fertile at higher temperatures and those plants set fruit over a longer period of time in the Southwestern United States. Some produce tomatoes the entire summer. Varieties optimized for heat in the Southeastern United States, however, are often accustomed to greater cloud cover and do not adapt well to the Western United States where there are few clouds and direct hot sun all day.
Heat Tolerant Tomato Varieties
Tomato varieties that set fruit above 90°F. include cherry-sized Nichols, Prescott and Punta Banda; and medium-sized Flamenco and Homestead 24.
Determinate and Indeterminate
Determinate tomato plants grow to a certain size and then quit. They produce most of their crop at one time and are suitable for canning. Indeterminate plants are true vines and continue to grow. Their crop is produced over the entire season and great for home gardeners who want to pick fresh tomatoes every day.
Days to Maturity
Early ripening tomato varieties may produce fruit in as little as 50 days after pollination. Early Girl, a popular variety, is one of the quickest to ripen. Most early tomatoes, though, were developed for cooler, northern climates and shut down production in summer heat. Beefsteak varieties can take up to 85 days to ripen. Indeterminate cherry and "current" sized tomatoes often grow in bunches and are more likely to have ripe tomatoes ready to pick every day.
Use Raised Garden Beds or Large Containers
Having a raised garden bed provides better moisture control. The soil and roots of growing plants will not get waterlogged during heavy rains. Complaints that raised garden beds overheat in the southwest can be addressed by providing afternoon shade to the garden and sides of the raised bed. Raised beds also make it easier to leach excess salts out of soil in the southwest desert through rain and watering.
A seven- to ten-gallon container can also be used, providing it is white or always shaded so the roots are not overheated. Drill four holes at the bottom of the sides for drainage unless there is a bottom hole raised off the ground. Do not use a saucer for the container unless it is placed upside-down or does not hold water.
Tomato plants should be rotated yearly. Divide your garden into four equal-sized sections. No garden section should grow nightshade family members (tomato, chili, including Bell pepper, eggplant, golden berry, petunia, potato, tobacco, and tomatillo) more than once every four years.
In other words, three-fourths of your garden should NOT be growing nightshade family members in any given year. Position all nightshade family members so that together they occupy only one-fourth of the garden.
This will prevent the accumulation of diseases in the soil that attack nightshades.
Tomato plants can tolerate a soil pH range of 6.0 (acidic) to 7.5 (slightly alkaline). For information on soil preparation and soil pH, see Soil Preparation.
Space tomato plants at least 24" apart and give them 6 square feet of space each. Planting closer together than 24" promotes fungal diseases. For shallow, raised garden beds, a 36" separation will provide more room for roots to grow without competing. Some varieties, especially indeterminates, will spread sideways even with a tomato cage and need at least 36" separation.
Some gardeners set out seedlings a month or more before the last frost date to get an early start on tomato production. When freezing temperatures are predicted, a ring of water-filled 2-liter soda bottles or tall water bottles are placed around the plants. Floating Row Cover or a plastic sheet with small holes is then placed over the top of the plant and the bottles until the temperature rises. A commercial product, Wall O' Water, can also be used, but is tedious to set up and seems more appropriate for northern climates.
Planting for Fall
In parts of the southwest desert, gardeners often grow vegetables fall to spring, then stop during the hot summer. Tomatoes, however, are sun-loving plants and do best if planted in the spring. Indeterminate cherry-sized tomatoes are more likely to ripen well into fall. Current-sized tomatoes will grow in January in Zone 9. For those getting a late start on planting tomatoes, the most prudent last planting date for fall crops is July 31 for early-ripening medium to large sized tomatoes; August 31 for cherry tomatoes, and September 30 for current sized tomatoes.
Transplanting Potted Plants
Put tomato seedlings in the ground when the danger of frost has nearly passed. Be prepared to protect from late frosts. Remove the entire pot, whether peat moss or plastic. Peat moss pots do not rot in our dry soil and retard root growth, regardless of claims that roots can grow through them.
Bury the tomato seedling stem up to the first true leaf on the stem. Remove any leaves on the stem that touch the soil. This will achieve the fastest, strongest growth and produce the highest yield. Some nurseries include instructions to place 2/3 of the seedling stem below ground. That will cause the seedlings to go into shock for the first month, and barely grow, but they will eventually recover and catch up to the others.
It should be noted that tomatoes are one of the few plants that can be treated this way. Nearly all shrubs and trees need their root crowns to be at or slightly above ground level.
Tomato plants do best with support if they need to be grown in confined spaces. Cylindrical cages made of field fence, or concrete reinforcing mesh, about 19" in diameter and 3 to 4' tall, with 6" long wire spikes on the bottom to anchor them into the soil, are recommended.
Concrete reinforcing mesh can also be used like a fence. Attach it, or field fencing, to steel T-posts. Tie vines loosely along the fence. Check the ties periodically to ensure stems are not being constricted.
Remove All Flowers for the First Four to Six Weeks
Prevent the plant from growing tomatoes by cutting off all flowers and fruit for the first four to six weeks after transplant. This will force it to put its energy into growing roots, leaves and stems. When you do allow flowering and fruiting, the plant will be large enough to grow more tomatoes. The total fruit yield for the year will be greater.
Sun and Shade
The tomato, like any summer fruit or vegetable plant, needs sun. How much sun depends on geographic location, temperature and time of year. In the American Southwest, 6-8 hours of full sun plus 50-60% shade in the afternoon is recommended when temperatures are under 90°F. Growing tomatoes in partial shade reduces water loss and sun scald and cools the plants so that they will be more likely to set fruit in the hottest part of summer. Latticework, sun shade cloth suspended 8' high, or tall plants can be used to shade the garden.
It should be noted that too much shade in cool temperatures can increase the likelihood of fungal diseases in susceptible varieties. On the other hand, when temperatures are over 90°F, provide 50% shade all day to give tomato plants a better chance of setting fruit.
By the first of September, the sun will be lower in the sky and there will be fewer hours of daylight. Provide more sun by removing overhead shade. By the first of October, eliminate shade altogether.
Water in the morning at the same time every day with the same amount of water. Check to make sure that 24 hours later, the top one or two inches of soil is dry.
If you are using containers or raised garden beds, and it rains, water as though there was no rain, or reduce water by no more than 25%. Water will reach the depth required and excess water will drain off.
Avoid watering in the late afternoon or evening because this encourages fungus infections in the soil. Also avoid getting water on leaves because this promotes leaf fungal infections in susceptible varieties, especially when mornings are cool.
Inspecting for Insects
Be sure to inspect closely for any insect activity. Pick off any insects found. Hornworms can look exactly like rolled-up, green leaves from the side. Inspect plants at midnight or very early morning for hornworms which feed on the outer plant at night and move to the interior of the plant during daylight. Aphids can be removed by jets of water.
One exception — leave the Pipevine Swallowtail caterpillars alone. If they are on your garden cage or tomato support,they are merely looking for a place to pupate and will be a chrysalis by the next morning. They don't eat human food plants and add interest to the garden.
Pests and Plant Placement
When all plants of a given species are planted in the same place, insect pests have an easy time finding them and making a general feast of the neighborhood. This is called mono-cropping and should be avoided in the vegetable garden.
To confuse insect pests, place a variety of plant species throughout the garden in seeming random fashion. It will not be truly random, because we must know which plants go well together and which plants do not. Placing plants in a vegetable garden is almost like seating guests at a dinner table.
Surround tomatoes with companion plants that ward off pests and attract beneficial insects. Basil and marigold are great companions for tomatoes. The aroma of Sweet Basil repels hornworm moths. Flowering basil attracts bees. One basil plant is needed for each tomato plant.
French marigold flowers, more than regular marigold, attract hoverflies, which prey on aphids. Marigold roots kill nematodes in the soil if planted the season before tomatoes are introduced.
Other good companions of tomatoes are onion and sage.
Some flowering plants may have to be grown in pots or separate garden beds to avoid interference with the tomatoes. Geraniums grown in pots are used as trap crops, luring aphids and leafhoppers away from other plants. In one report, geraniums are said to repel tomato fruitworm moths, although this needs to be verified.
Sweet Basil is a warm weather plant. Seedlings can be damaged by nighttime temperatures under 50°F and must be planted a few weeks later than tomatoes. Once basil has been in the ground four months, it tolerates temperatures in the low 40's. Sweet Basil has the strongest aroma and best hornworm moth deterrence value of the basils.
Plants that do harm to tomatoes should not be grown in their vicinity. Some bad companions release chemical compounds into the soil that harm tomato plant growth or fruiting. Others vigorously compete for the same nutrients. Beans, dill, fennel, kohlrabi and potato are bad companions. Corn is also a bad companion because corn and tomatoes both share a common parasite: the corn earworm, also known as the tomato fruitworm. For those reasons, tomatoes should not be planted where bad companions grow or grew the previous year.
Growing tomatillos is like growing tomatoes with one difference. Some tomatillo varieties are not self-fruitful and two or three others must be flowering nearby for pollination. The fruit are ripe when the husk splits or when the husk is well filled out and the fruit begins to soften.
All Foliage, No Flowers
This occurs when the plant has been given too much nitrogen. Ammonium sulfate may have been used to acidify the soil. Ammonium sulfate is a high nitrogen fertilizer and should not be used with tomatoes. Also, you may want to avoid rotating tomato plants into a garden bed where nitrogen-fixing legumes have been grown the year before.
The immediate solution is to sprinkle one-half to one tablespoon of superphosphate pellets, once only, on the ground under the plant. Daily watering will gradually dissolve the phosphate and make it available to the roots. This should induce flowering within two weeks.
Many Flowers, No Fruit
This normally happens when the tomato variety cannot set fruit in high temperatures. At times the blossoms on top of the plant will fail, but those in the shady middle, bottom or north side will set fruit. If there is no pollinator, place blooming flowers nearby to attract bees. Pollination by hand is easy. Just tap the stem behind the blossom and it will self-pollinate, assuming that the temperature is suitable.
Dark Brown Spot on Bottom
A dark brown, leathery spot on the bottom of a tomato is called Blossom End Rot. The causes are inconsistent watering, insufficient water, cutting roots during weeding, or insect damage to the stem or the fruit. Any of these will result in poor calcium ion distribution inside the plant. Insect damage sometimes results in early fruit ripening. Another cause is growing a tomato variety which grows its roots slowly and requires twice the amount of water until the roots catch up. Some tomato varieties are more prone to blossom end rot than others.
To avoid Blossom End Rot, inspect for, and remove, any caterpillars or other insects. Water every day at the same time with the same amount of water. At least 6-8 cups of water is needed per plant. Be sure to mulch the soil around the plant to retain moisture. This is not a calcium deficiency in the soil but rather a problem with the transport of calcium within the plant. American southwest desert soils have sufficient calcium.
Split Skin and/or Scarring
Split skins and scarring are caused by irregular water amounts, especially too much water. Know how much water the plants are getting every day. An increase in daytime temperature can cause tomatoes to grow faster, resulting in higher water needs. Sporadic heavy rains may cause split skins in spite of your best efforts. Assuming no rain, the top one to two inches of soil should be dry 24 hours after watering. Some tomato varieties are more prone to skin splits than others.
Fruit Ripen Too Small
Two possible causes:
 The plant is not mature enough to have the leaf area and root length required to support the number of tomato fruit in production.
 Too much competition from the roots of other nearby plants in a garden bed or not enough soil in the container. Containers should hold at least 7 gallons of soil for each plant. Tomatoes grown in raised garden beds one foot deep should have at least 6 square feet of space to themselves, excluding nearby Sweet Basil.
Cut back on the number of fruit allowed to develop at one time until the plant grows larger. Never remove leaves from the plant. They provide energy for growth and needed shade for the fruit.
Holes in Fruit
This discussion assumes that the tomato plants are protected from birds.
Small holes, often one-eighth to one-quarter inch in diameter, are caused by tomato fruitworms. Much larger holes are often caused by grasshoppers.
Fruitworm and other caterpillar eggs can be controlled with Green Lacewing larvae. Once caterpillars appear, Bacillus Thuringiensis is recommended.
An effective defense for grasshoppers is to spray green and ripening tomatoes with a garlic-pepper solution before they are eaten. The solution is easy to make. Place four Habanero peppers and four large garlic cloves in a blender and mince. Blend in two cups of water and let stand out of direct sunlight at room temperature for one day. Strain into a 24 ounce spray bottle with water added to fill. The solution must be re-sprayed after every rain.
Large Whitish Spot on Fruit
The whitish spot is called Sun Scald. Sometimes there will be a smaller center of wrinkled skin inside the whitish spot. This condition is caused by too much direct sun. The best solution is to give the tomato plant afternoon shade and avoid removing any leaves.
Yellow Shoulders or Patches on Fruit
Tomatoes with yellow shoulders or patches may also have a green area inside the yellow. This condition has two main causes.
 The soil is deficient in potassium. Add compost to the soil before planting or use tomato fertilizer according to directions.
 When leaves have dark spots that spread to stems and form cankers and the fruit has yellow blotches, this is spotted wilt virus spread by thrips. There is no effective treatment except to cut down the plant and discard it. Do not put it into a compost pile to avoid spreading the virus.
Fruit Do Not Ripen
Some tomato varieties take a long time for each fruit to ripen, up to 85 days. Know what is normal for your variety.
In spring, tomatoes may delay ripening when temperatures rise above 85°F because the production of chemical compounds that produce color begin to shut down. The plant also has to divert more of its energy to growing deeper roots, further delaying ripening. One solution is to place the tomatoes in 50% shade all day to reduce internal temperatures.
For heat-tolerant tomato plants, reducing the amount of water given to each plant may also encourage ripening. The first tomatoes to turn color will often be the ones at the shady bottom of the plant.
If a plant has been ripening fruit but stops doing so many months after planting, the cause is less sunlight at the end of summer, especially with many tomatoes on the plant. Tomatoes are more likely to ripen when they receive more than 12 hours of sunlight a day. To overcome shorter daylight hours, remove all sources of shade and give the plant full sun if it does not already have it. Cut off all flowers if it is still producing them. Remove any small green tomatoes that have not achieved full size. Reduce daily water to 4 to 6 cups per plant.
Cold temperatures can also slow ripening. When it gets too cold, the remaining tomatoes can be picked and placed inside. If they are green, place them where they will receive direct (through a window) sunlight part of the day. The sunlight will cause them to partially ripen. Partly ripened tomatoes, with a blush of yellow or red, will finish ripening in a bowl containing apples or a banana.
Tomato Plant Small or Stops Growing
If tomato plants (excluding those grown in pots) are not over 3' tall after 8 weeks, and there are no disease symptoms, the likely causes are
 Too much competition from roots of other nearby plants in a garden bed. Make a choice about which plant to remove to give remaining plants more separation.
 the soil is deficient in potassium and possibly other nutrients as well. In poor fertility conditions, an indeterminate plant can even stop growing. Tomatoes are heavy potassium feeders. Compost containing well aged (and watered) manure must be mixed into the soil in the fall before next year's planting.
 Overwatering can be a problem with dry heat tolerant tomatoes, especially those that have been in the ground more than three weeks. This is often accompanied by yellow leaves. Reduce watering to one-half the usual amount and see if they grow faster without becoming wilted.
Rust- Bronze-Tinged or Brown Stems or Leaves
Green stems develop a bronze tinge starting from the ground up. Leaves may quickly dry out without any black or yellow spots, then become brown and brittle and drop from the stem. An entire section of stem and leaves may dry out and turn brown within 24 hours. The cause is the tiny Tomato Russet Mite, which can only be seen under 16x magnification. These mites show up in very dry, hot conditions. They infect nightshade family plants and are hosted by wild nightshade species such as Sacred Datura.
Wettable sulfur, sold by nurseries, can be used as a control. Miticides which contain Pyrethrins and Neem seed oil are also effective. Follow directions for best results and do not overuse. Pyrethrins are hard on tomato plants. Neem seed oil by itself might be better but is very expensive. Act fast or these mites will destroy every tomato plant in your garden within days.
Several factors cause yellow leaves.
Fungal, bacterial and viral diseases may be a problem, especially with heirloom tomatoes. See Texas Aggie Tomato Problem Solver. Cut off yellow leaves with scissors when they occur, and pick up leaf litter on the garden bed to reduce the spread of any fungus.
Too little or too much water is another possibility. If leaves are limp in late afternoon, add more water in the morning. Overwatering can be a problem, especially if plants are not grown in raised garden beds or in well-draining soil. Some heat-tolerant plants do not like excessive water even when loaded with fruit.
Too little sun at the bottom of a bushy plant can result in bottom leaves turning yellow. This is nothing to worry about.
Insects such as aphids and hornworms can damage leaves and stems, turning them yellow and even brown. Remove insects when they are found.
Too little magnesium in the soil. If the leaves have green veins but are yellow in between the veins, the cause might be a lack of magnesium. Sprinkle a tablespoon of Epsom Salts around the base of the tomato plant and water it in during the normal watering time. The yellow spots should fade away in a week. If not, apply one more time. If there is no improvement, the cause is probably not magnesium deficiency.
Too little nitrogen in the soil. This is rare in prepared vegetable garden beds, so test for soil nitrogen content. Adding a standard tomato fertilizer according to package directions should immediately solve a nitrogen insufficiency problem.
Odd Shape Fruit / "Nose" / "Horns" on Fruit
Very hot or cold temperatures just after fruit set can result in extra locules being produced in the fruit. Locules are the sections of the tomato that can be seen when it is sliced horizontally. The extra locule can grow out to the side, resulting in a "nose" or "horns" on the tomato. This is harmless.
Exposure to some pesticides can result in deformed fruit. Avoid using synthetic pesticides and herbicides in the garden.
Insufficient phosphorous availability in the soil results in reddish-purple stems and leaves. Some tomato varieties may display leaves colored green on top and purple underneath, with purple veins. This condition can be caused by a soil pH being outside the optimum 6.0-7.0 range, so test your soil pH.
For immediate results, use a standard tomato or vegetable fertilizer as directed, or sprinkle one-half tablespoon of superphosphate on the ground under the plant and water daily. If the soil is too alkaline, add two tablespoons of vinegar to each gallon of water daily.
For long-term prevention, see Soil Preparation.
Tomato Purple Leaf Disorder has been observed in Florida. This disorder is first seen on the top leaf surface, between the veins, then spreads to the entire leaf surface. Parts of the leaf shielded from the sun remain green. The effect on the fruit and the plant long-term remain unknown. It is not caused by any soil deficiency.