Disease Resistance
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. The greater the disease resistance, the better. Heirloom varieties tend to have less disease resistance.

Heat Resistance
The pollen of most tomato plants becomes sterile at 90° F and tomato production often ceases during hot periods such as the last half of June. Pollen of the Tomato variety Heatwave, however, remains fertile up to 95° F and the plant sets fruit over a longer period of time in the desert southwest. The varieties Super Sioux and Solar Fire are also productive in high temperatures.

Determinate and Indeterminate
Determinate tomato plants grow to a certain size and then quit growing. Indeterminate plants are true vines and continue to grow. If they go dormant during the hottest months, prune them back by one-third in the fall, and this will provoke new vigor and result in another crop until frost.

Best Tomato Varieties in Oracle
Some of the most prolific tomato plant varieties in Oracle in mid-July, 2010, have been the heirloom Super Sioux and the hybrid Bush Goliath. They continue to produce the largest number of new tomatoes during very hot weather.

Use Raised Garden Beds
Having a raised garden bed provides better moisture control. The soil and plant roots will not get waterlogged during heavy rains.

Spacing
Space tomato plants at least 24" apart. If you follow the rest of the cultivation tips on this page, by June your plants could be nearly touching. 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.

Transplanting Potted Plants
Remove the entire pot, whether peat moss or plastic. Peat moss pots retard root growth, regardless of the claim that roots can grow through them. Coconut fiber pots may be OK.

Place tomato plants so that the top of the potted soil is level with the garden bed soil. This achieves the fastest, strongest growth. Some indeterminate varieties have instructions to place 2/3 of the plant below ground. That will cause them to go into shock for the first month, but they will eventually recover, catch up and surpass their determinate cousins.

Support
Tomato plants need support. Wire tomato cages, 3½ feet high with four hoops, work well on most determinate varieties. Indeterminate varieties will need a taller, perhaps wider cage. Make sure that the ends of the bottom wires are even so the cage will stay upright when pushed into a raised garden bed with a hard soil bottom.

Remove All Flowers Before June
Prevent the plant from growing tomatoes by cutting off all flowers and fruit until the first of June. 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. The plant should be 24" to 30" tall by June.

Shade
Provide 50% shade for tomato plants all day in the desert southwest. Lattice or sun shade cloth can be used. This will reduce water loss, reduce sun scald, and cool the plants so that they can set fruit further into summer. Shade will also discourage visits from Leafhopper insects which carry the Curly Top virus.

Periodic Fertilization
For tomatoes, use a commercially made tomato fertilizer added to water. The one most widely available has a nitrogen-phosphorous-potassium formula of 18-18-21 and contains a small amount of magnesium, making the traditional use of Epsom salts to prevent yellowing of leaves unnecessary and undesirable. Follow directions on the package for dilution and frequency. Start fertilizing the first day the seeds or transplants have been put into the garden bed. Avoid fertilizers where the first number (nitrogen) is higher than the second number (phosphorous).

Do not depend on bagged soils with added fertilizer. These have the wrong formulation for tomatoes. If you did use this type of soil, add tomato fertilizer in the water at intervals anyway. When fertilizer is added to bagged soils, it is usually in low concentration and more phosphorous and potassium are needed.

Soil Acidity
Tomato plants are tolerant and accept soil pH between 5.5 (acidic) and 7.5 (slightly alkaline). Oracle soil is usually pH 7 (neutral). Composted mulch or coffee grounds spread on top of the soil provide the best long-term soil acidification. A quicker method is to add two tablespoons of natural apple cider vinegar to one gallon of water when watering the plant. Brown vinegar adds a few trace minerals to the soil, but clear vinegar also works.

Avoid ammonium sulfate to acidify the soil because this is a high nitrogen fertilizer. Tomato plants grown in high nitrogen soils tend to be all foliage and no tomatoes.

Watering
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. As days get hotter, or the plants become larger, tomatoes will need more water. Coordinate your watering with rainfall. 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 still cool.

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.

Good Companions
Surround tomatoes with companion plants that ward off pests and attract beneficial insects. Basil and marigold are great companions for tomatoes. The aroma of basil repels hornworm moths. Marigold roots kill nematodes in the soil, especially when planted the season before tomatoes are introduced. Marigold flowers attract hoverflies which prey on aphids and their aroma distracts some pests. Other good companions of tomatoes include borage, geraniums, nasturtiums, onion, sage and sunflowers. Geraniums and nasturtiums, grown in pots, are used as trap crops, luring aphids and leafhoppers away from other plants. Nasturtiums also attract hoverflies.

Basil is a hot weather plant that can be damaged by nighttime temperatures under 50°F. It must be planted weeks later than tomatoes. Sweet Basil and Purple Ruffles Basil can succumb to a soil fungus, so consider flavored varieties like Spicy Globe, Lemon, or Cinnamon Basil which are more resilient.

Bad Companions
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.

Rotation
Tomato plants should be rotated yearly. No garden bed should have tomato family members (tomato, eggplant, pepper, potato, tomatillo, petunia) more then one year in four. That is, three years should pass without tomato family members before a given garden bed sees tomato plants again. This will prevent the accumulation of diseases in the soil that attack nightshade family members.

Grow tomatillos like tomatoes except use somewhat less water. Periodic fertilization is unnecessary. Avoid bagged garden soils with added fertilizer. Do not rotate into a garden bed where a legume has been growing because tomatillos do not like high nitrogen soils. The fruits are ripe when the husk splits or when the husk is well filled out and the fruit begins to soften.

All Foliage, No Fruit
There are two causes of this condition. (1) The plant may have been given too much nitrogen. See Fertilization recommendations above. Another possibility is that ammonium sulfate has been used to acidify the soil. Ammonium sulfate is a high nitrogen fertilizer and should not be used with tomatoes.
(2) Blossom drop before pollination may be caused by temperatures below 55° F or above 90° F. Also, there may be no pollinator, or blossoms may be knocked off by high winds or heavy rain. Pollination by hand is easy. Just tap the top of the blossoms gently and they will self-pollinate.

Tomato Fruits Ripen Too Small
It takes a certain amount of leaf area and root length to produce each tomato fruit. Experienced gardeners cut off all blossoms appearing before June in order to give the plant more time to develop roots and leaves. If the number of tomatoes on the plant exceeds the root structure and leaves to support them, some will be too small. Cut back on the number of fruits allowed to develop at one time if some tomatoes ripen when too small.

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 have the tomato plant in 50% shade the entire day or full afternoon shade.

Dark Brown Spot on Bottom
A dark brown, leathery spot on the bottom of a tomato is called Blossom End Rot. It is caused by a calcium deficiency due to inconsistent watering or cutting roots during improper weeding. Water every day at the same time with the same amount of water. 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. Desert southwest soils have sufficient calcium.

Yellow Shoulders on Fruit
Tomatoes with yellow shoulders or patches may also have a green area inside the yellow. This condition has several probable causes, from high temperature, too little potassium or too much magnesium. Yellow shoulders can be alleviated by using a proper tomato fertilizer (see Periodic Fertilization, above) and avoiding the use of Epsom salts which upset the magnesium/calcium balance in the soil. Increasing soil acidity (see Soil Acidity, above) may also help.

Tomatoes Do Not Turn Red
This is caused by overwatering. Keep watering at the same time every day, but reduce the amount. The top one or two inches of soil should be dry 24 hours later.

Split Skin and/or Scarring
Split skins and scarring are caused by irregular water amounts - too much water, then too little, then just enough, etc. Be sure to account for rainfall when watering, and 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.

Yellow Leaves
Several factors cause yellowing leaves. It can be insufficient nitrogen in the soil, and the solution is to apply tomato fertilizer according to directions. The long term solution is to have plenty of organic matter such as composted mulch and composted manure in the soil.
Yellow leaves can also be caused by insufficient water, so try not to let the soil dry out completely below the top three inches.
If there are brown spots in the middle of yellow areas, the plant may have a fungal disease. See Texas Aggie Tomato Problem Solver.

Rust- Brown- or Bronze-Colored Leaves
Tomato Russet Mites can cause bronze-colored lower stems and leaves. These tiny mites can only be seen under 20x magnification. Wettable sulfur, a fine powder sold by nurseries, is often recommended as a control. See Troubles in the Tomato Patch. These mites can destroy a tomato plant and its fruit quickly.

Purple-Reddish Leaves
Insufficient phosphorous results in reddish-purple stems and leaves. Use tomato fertilizer to prevent this problem.

Stunted Tomato Plants, Slow Growth
A potassium deficiency causes slow growth, stunted plants, crinkled new leaves, pale older leaves and bronze spots near large veins. Use tomato fertilizer to prevent this problem.