Tomatoes

History

The tomato is a member of the Solanaceae family, also known as nightshades, which includes crops such as the Irish potato, pepper, tomatillo, and eggplant (Figure 1).

The first wild tomato plant had bright red, cherry-type fruit and is thought to be native to the Andes Mountains region of Peru and Bolivia. Tomato spread to South America and Central America by the natural migration of Indigenous peoples. Confined to the Americas for several thousand years, it was bred and selected for larger fruit (which varied greatly in appearance), likely in Mexico beginning with the Aztecs and Toltecs. There it was traditionally companion planted with corn.

Christopher Columbus’s arrival in the New World prompted the spread of the tomato plant to Europe via Spanish explorers by 1550. In Spain the tomato was called “pome dei Moro” or “Moorish apple”; in Italy, “pomo d’oro” or “golden apple”; and in France, “pomme d’amour” or “apple of love.” Development of new varieties continued across those European countries, most popularly centralized around the Mediterranean region. English-speaking countries were skeptical of the fruit, as tomato is in the deadly nightshade family and the red color was thought to signify its poisonous nature. Tomato leaves and immature fruit contain the toxic alkaloid tomatine.

By the 1700s, tomato plants were grown in the U.S. by many gardeners, even Thomas Jefferson himself, but still the poisonous myth lingered. This cultural opposition began to change by 1812 with help from Creole cuisine in New Orleans, as tomatoes were fundamental for many dishes like gumbo and jambalaya. By the mid-1800s, tomatoes were commonly grown and used across the U.S. See Figure 2.

In the 19^th century, the tomato had to overcome another myth that it caused cancer. This was eventually disproved by scientific evidence showing the contrary; it actually contains high levels of lycopene, an antioxidant that has cancer-fighting properties. This antioxidant is also found at lower levels in watermelon and grapefruit.

Today, tomato is the most commonly grown crop in a home garden and each American eats a yearly average of 23 pounds of processed tomatoes (e.g., ketchup, tomato sauce). Although the tomato is botanically a fruit, it is treated and classified as a vegetable.

Varieties

Tomato varieties are grouped by plant growth habit: determinate or indeterminate (indicated in Table 1 with a “D” or “I” after the variety name). Determinate varieties (sometimes called bush types) generally produce fruit during a shorter harvest period (3-4 weeks), as stem growth stops at a “determined” height with a terminal (final) bud. In contrast, indeterminate varieties have a stem that continues to grow “indeterminately” until the frost, producing fruit progressively over a longer harvest period (5-6 weeks). Determinate varieties often grow 3-4 feet in height and indeterminate varieties grow 6-7 feet in height. Indeterminate varieties must be grown on a tall, strong trellis.

The thousands of tomato varieties can be divided into the following types: (1) fresh market and beefsteak, (2) heirloom, (3) Roma/paste, (4) grape and cocktail, and (5) cherry (see Figure 3). Tomato fruits ripen to a variety of colors, from the traditional bright red to yellow, orange, pink, green, or purple. Some varieties are selected for superior flavor or sweet-tasting fruit, heat tolerance (heat set), uniformity, productivity, or disease resistance.

Fresh market or beefsteak types produce more traditional, large, bright red, round tomatoes that are sometimes called “slicers” as they are used sliced on sandwiches and salads. Pink Girl and Carolina Gold are two fresh market/beefsteak varieties recommended for Louisiana that do not have red flesh. This type includes varieties with high disease resistance and average fruit weight.

Heirloom tomatoes are generally indeterminate, requiring trellising and pruning to manage the plants properly. Most varieties have little disease resistance and the fruit are usually thin-skinned, soft, and tend to crack. Heirloom tomatoes are attractive because many varieties are very flavorful, col­orful, come in many sizes and shapes, and have interesting names. Greater care and management are required for heirloom types and if being grown organically, they should be grown in high tunnels for the greatest chance of success. There are hundreds of varieties of heirloom tomatoes avail­able. Heirloom tomatoes include varieties whose seeds have been saved for at least 50 years and can be saved each season and replanted. In Table 1, varieties are grouped under heirloom even if they could have been categorized under another type based on size and shape. For example, popular heirloom varieties like Brandywine, Carbon, and Cherokee Purple are also larger and good for slicing like fresh market/beefsteak types. San Marzano is a famous Italian heirloom that is also used in the same way as other Roma or paste tomato varieties, and Yellow Pear is also a cherry tomato type. All of these are listed under heirloom.

Roma/paste tomato types include varieties with rather uniform, plum-shaped, medium red fruits, averaging 3-5 ounces. Varieties in this type have thick walls, few seeds, and good flavor; they are ideal for tomato sauce, paste, puree, ketchup, juice, and canning. All of the Roma/paste types recommended for Louisiana are determinate varieties and they are traditionally harvested in bulk, all at one time, and preserved.

Grape, cocktail, and cherry types are faster-growing and produce smaller fruits that vary in color (red, yellow, orange, purple-black) and weigh between 1/2-2 ounces. These types are generally very sweet-tasting and productive, with varying disease resistance. Grape and cocktail tomatoes include varieties that produce fruit at the higher end of the weight range and often have a more elongated shape. Sungold is a variety of cherry tomato that holds the title for the sweetest fruit, making them very popular among children.

Tomatoes have either open-pollinated (including heirloom) or hybrid varieties. All tomato varieties produce perfect, self-pollinating flowers (containing both male and female parts; see Figure 4), so there is usually no need to isolate different varieties when planting in order to save seed. For older varieties (heirlooms), it is recommended to separate different varieties by a distance of 10-50 feet to prevent cross-pollination (this difference is due to the flower structure of older tomato varieties).

If growing tomatoes in a green­house, it is recommended to select a greenhouse variety (indicated in Table 2). These varieties have been bred specifically for greenhouse condi­tions — lower light, higher humidity, and high temperature — and have better disease resistance than field types. Nearly all greenhouse va­rieties are indeterminate hybrids so that they will produce over a long harvest season. While non-greenhouse types can also grow in a greenhouse, the yield and quality may be reduced. In controlled environments (greenhouse or high tunnels), blowing/shaking of flowers or using bumble bees is required to ensure adequate pollination.

It is recommended to select disease resistant-varieties whenever possible. See the recommended tomato varieties for Louisiana in Table 1.

Table 1. Recommended Tomato Varieties for Louisiana

When and How to Plant

Tomatoes are warm season, frost-sensitive annuals. Tomato seeds should be started inside 6-8 weeks before the desired transplant date (refer to theTomato Planting Guide, Table 2). Using seed germination trays (with at least 1.5-inch diameter cells; larger cells work well for this crop too), plant 1 seed per cell at a shallow depth, about 1/8-inch deep; just deep enough to be covered with a thin layer of soilless potting mix. Seeds will germinate best in a warm, well-lit area in soil temperatures between 60-85 degrees F (tomato seeds will germinate very slowly in cooler soil). The minimum soil temperature for germination is 50 degrees F; maximum is 104 degrees F. It is important to keep soil moist, which usually requires daily light watering. A seedling heat mat and plastic dome lid are helpful in maintaining ideal germination conditions. Once several true leaves develop, it is recommended to move plants into larger, 3- to 4-inch pots to allow for more root growth before transplanting outside. At this stage, seedlings can be kept at 60-70 degrees F.

Tomato plants easily survive transplanting, but seedlings are susceptible to cold-shock and growth may be stunted if soil and air temperatures are too low. Aim to transplant outside when the temperature is between 65-75 degrees F (minimum temperature of 60 degrees F; there should be no danger of frost) and ideally during a cloudy day or planting late in the day or even at night to reduce wilt. A few days before planting transplants outside, it is recommended to follow a hardening-off process to transition seedlings to outdoor conditions. Refer to the Tomato Planting Guide (Table 2) for the recommended spacing when transplanting.

Tomato plants should be planted about 6 inches deep, or to the lowest leaf, as roots will form on the buried stem and this will encourage a stronger plant. This method will also correct a plant that has bent toward the sun to an upright position (see Figure 5).

Tomato plants are sensitive to cold temperatures below 50 degrees F and hot temperatures above 95 degrees F as this may cause blossom drop, poor fruit set, or cat-facing (deformed fruit). The optimum growing conditions are warm days (80-85 degrees F) and cooler nights (60-70 degrees F).

Table 2. TOMATO PLANTING GUIDE

Where to Plant

Tomatoes are a warm season crop, and a well-drained clay or loam (sandy or silty) soil and full sun (6-8 hours/day) are recommended. Tomato plants prefer a soil pH between 6.0 and 6.8 but will tolerate acidic soil as low as 5.5. Avoid planting in heavy soils and low areas prone to flooding. It is recommended to plant tomatoes in box beds or in traditional raised garden rows that are about 6 inches tall to ensure good drainage and to prevent disease. In all types of gardens, it is recommended to add a 2- to 3-inch layer of compost, peat, rotted hay, or other organic matter and mix into the soil to optimize plant health. This is especially important for tomato plants as they thrive in soil high in organic matter, phosphorus, and calcium (to prevent blossom-end rot, use calcitic lime or gypsum if needed). Be sure the soil is not too high in nitrogen.

Reflective plastic mulch — or a plastic fabric/film mulch — is recommended to increase soil temperature, yield, fruit size and quality, while controlling weeds. White plastic is recommended for growing tomato plants in temperatures above 85 degrees F, as this will keep the soil cooler during warm weather fruit production. Black plastic is only recommended for cooler climates and during the spring in Louisiana. Drip irrigation is also recommended when using plastic mulch to maintain ideal soil moisture and to encourage productive plants.

Each season, rotate plant families — avoid planting crops from the same plant family in the same area of the garden — to reduce disease and pests. A longer crop rotation of 4 years is recommended for Solanaceous crops like tomatoes to reduce pest pressure and risk of disease.

Plant Care

Watering

Check for adequate soil moisture every 2-3 days. The soil should remain moist, but take care to not oversaturate as this encourages blossom-end rot. Drip irrigation helps to meet the high-water demand for this crop, about 1-1.5 inches per week depending on soil type and temperature, which is especially important during the fruiting stage. Deep watering is important to strengthen the root system. If plants are stressed for adequate water, this will significantly impact tomato production.

Fertilization

Insufficient potassium may lead to yellow shoulders on fruit and a tough, white core during hot summer temperatures. Blossom-end rot, a very common tomato nutritional disorder, is caused by lack of calcium. Soil may have sufficient calcium levels, but if the gardener fails to water enough, calcium may not be dissolved in the soil for root uptake. If watering practices are corrected and blossom-end rot persists, conduct a soil test and discuss results with a local county extension agent.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Alternatively, a synthetic fertilizer may be used at a rate of about 1.5 pounds (3 cups) of 13-13-13 for every 25 feet of row or 75 square feet. Broadcast, or sprinkle evenly, over the soil and then mix in about 3-6 inches deep using a rake. Supplemental sidedressing, or reapplication of synthetic fertilizer, is recommended when the first immature fruits are visible. Sidedressing is the addition of fertilizer to the soil around already established plants when the plant begins to fruit or vine, primarily to provide nitrogen. When using synthetic fertilizer, sprinkle 2 tablespoons around each plant, keeping it about 6 inches away from the plant stem; water into the soil. Indeterminate tomatoes require the application of additional sidedressing every 3-4 weeks until the end of the crop. Fish emulsion is a good, quick-release source of nitrogen if using organic fertilizers.

Support

Staking of tomatoes improves fruit quality by keeping plants and fruit off the ground, and they are easier to harvest than ground tomatoes. Determinate tomato plants are often staked even though the stems do not grow tall. Indeterminate tomato plants must be supported to train the stem to grow vertically and support the weight of the fruit on very tall stems; this will also optimize yield and fruit quality. There are many options to support tomato plants, but cages are not recommended as they prohibit air circulation and increase risk for disease. Here are three methods to support tomato plants:

1. Use one wooden stake per tomato plant (recommended for a few plants). Drive 4- to 5-foot (determinate) or 8-foot (indeterminate) by 1-inch square wooden stakes into the ground (about 12 inches deep) before transplanting at the recommended plant spacing intervals (about 24 inches). One transplant should be planted beside each stake. Once the seedlings are 12-15 inches tall, secure to the stakes using an elastic nylon band, tying in a loose loop to prevent future stem girdling. Continue securing the plants to the stakes for every 12-15 inches of growth. See Figure 6 and this video on the method; start at 3:30.
2. Use the Florida Weave Technique (recommended for a row of plants). Place a metal T-post at the end of each row and one in the middle; then place 4- to 5-foot (determinate) or 8-foot (indeterminate) by 1-inch square wooden stakes between every few tomato plants. When the plants are 12-15 inches tall, use garden, tomato, or nylon twine to run lines about 10 inches above the soil. On each side of the row of plants, weave between each plant, and tie the twine to the stakes. In this method, the plant is never tied to the twine or stake. It is recommended to weave additional levels of trellis for every 12-15 inches of plant growth, or about 12 inches above the last support weave. Watch this helpful video tutorial on the Florida Weave System.
3. Use a vertical trellis (recommended for a row of plants; minimal staking required). Drive metal T-posts that are 8-10 feet tall about 2 feet into the ground between every 4-5 tomato plants. This will likely require a T-post driver or pounder tool. Then, hang a heavy single-strand wire (about 9 gauge) between each post or attach another structure above. From this wire/structure, hang garden, tomato, or nylon twine down to each tomato plant. Attach the twine to the base of each plant in a very loose knot that won’t be at risk for choking the stem as it grows. Start wrapping the stems around the string early, taking care not to pinch the leaves, and continue to do so as the plants grow. In this method, the plants are never tied to stakes or posts (see Figure 7). This video is helpful in showing how to set up the vertical trellis; this video describes the process of winding twine around the stems. For someone who is more skilled in carpentry, this video shows a simple but more sturdy design for a vertical tomato trellis that could function as a permanent addition to a raised garden bed.

   

Suckering and Pruning

Pruning and suckering are essential for optimal fruit size and yield, while also controlling pests and preventing disease. Pruning is practiced to establish a desired balance between vine growth and fruit growth. Little to no prun­ing results in a plant with a heavy load of smaller fruit. Moderate pruning results in fewer fruits that are larger and easier to harvest. Pruning can result in earlier maturity of the crown fruit and im­proves spray coverage and pest control. The amount of pruning that is recommended is dependent on the specific variety, the season, and growing conditions.

Removing suckers is an ongoing process of removing the buds or suckers that would produce additional side shoots off the main plant stem. Suckering can be done by pinching off shoots by hand unless they have grown more than a few inches; then sharp snips or clippers should be used to prevent damage to the plant during removal. See Figure 8.

1. 1. Here is a short, simple video on how to sucker and prune tomato plants.
   2. Here is a longer, more detailed video on how to sucker and prune tomato plants, along with additional helpful tomato-growing tips.

Indeterminate varieties should be pruned to one or two main stems, removing all suckers along those main stems. It is generally not recommended to prune determinate varieties as they have a limited stem growth, are generally bushier, and are less vigorous. For all varieties, be sure to prune the lower leaves/stems to keep the base of the tomato plants clear; there should be no leaves touching the ground.

Weeds

Plastic mulch will control most of the weeds; hand-pull weeds close to the plant, especially in the planting holes. Organic mulches such as hay and straw may also be used to control weeds in plant rows.

Insect Pests and Disease

Aphids and thrips are common insect pests for tomato plants and can transmit harmful viruses like tomato spotted wilt virus and tobacco mosaic virus. Tomatoes are susceptible to viruses (e.g., tomato spotted wilt virus and tobacco mosaic virus), fungal diseases (e.g., anthracnose), and physiological disorders (e.g., blossom-end rot and sun scald). Many tomato varieties are resistant to specific diseases, and these should be selected and planted — especially if the garden has been afflicted by one or more diseases in previous growing seasons. Generally recommended tools for prevention are using reflective mulch; avoiding overhead irrigation; and crop rotation. See Table 3 to aid in diagnosis and management of some common tomato insect pests and diseases.

Table 3. Organic and Natural Management for Common Tomato Insect Pests and Diseases

Harvest and Storage

Tomatoes may be harvested unripe and green, or at any stage of ripeness, usually marked by a color change to red, pink, orange, yellow, or purple. Fruit can be harvested with just a blush of color, as ripening continues after harvest. For the best-quality taste, harvest ripe fruits that are firm, glossy, and easily dislodge from the plant. Harvest the fruit by hand, lifting from the plant. Remove the pedicel (stem) to encourage ripening and to prevent the bruising of other fruit. During peak production, tomatoes may be harvested 2-3 times per week for at least 3-4 weeks for determinate varieties or 5-6 weeks for indeterminate varieties, or until fruit production stops. The fruit is bruised easily and should be handled with care postharvest.

Ripe tomatoes stored at 50-70 degrees with high humidity (85-95%) will hold for 4-7 days; green or partially ripe tomatoes for 1-3 weeks. Take care not to store tomatoes below 50 degrees F as they are cold sensitive, and taste and texture will be adversely affected.

Preserve tomatoes by canning, drying, or freezing.

Tomatoes are Nutritious and Good for You

Good source of Vitamin A

Important for eye health, a strong immune system, and cell growth

High in Potassium

Essential for body function, especially the heart, kidney, nerves, bones, and muscles

Rich in Vitamin C

Important for bones, skin, blood vessels

Contains the carotenoid Lycopene

Antioxidant that may prevent cancer and improve heart health

Recipes

Louisiana Harvest of the Month recipe: Tomato Cucumber Salad

Video on how to cut tomatoes

Common methods of preparing and cooking tomatoes

Taste-testing ideas: bruschetta, salsa, chili, roasted tomato soup, spaghetti sauce, baked tomatoes with cheese, Panzanella

Other websites with many tomato recipes:

Food Hero 

SNAP-Ed Arizona 

SNAP-Ed San Francisco 

Produce for Better Health Foundation 

Sources

• Southeastern Vegetable Extension Workers, 2020 Southeastern U.S. Vegetable Crop Handbook
• LSU AgCenter, Louisiana Vegetable Planting Guide
• LSU AgCenter, Louisiana Commercial Vegetable Production Recommendations
• LSU AgCenter, Vegetable Gardening Tips: Tomatoes
• UF Extension, Planting Guide
• UF Extension, Vegetable Production Handbook of Florida
• Texas A&M AgriLife Extension, Vegetable Varieties for Central Texas
• Texas A&M AgriLife Extension, Easy Gardening: Tomatoes
• Texas A&M AgriLife Extension, Commercial Crop Guides: Tomato
• UT Extension, Plant Diseases: Foliar Diseases of Tomato
• Connecticut Agricultural Experiment Station, Stemphylium Gray Leaf Spot of Tomato
• Alabama A&M and Auburn Universities Extension, Bacterial Spot of Tomato and Pepper
• Alabama A&M and Auburn Universities Extension, Blossom-End Rot in Tomatoes: Causes and Prevention
• Alabama A&M & Auburn Universities Extension, Crop Production,
• UMass Extension Vegetable Program: Disease, Insect, and Mites Fact Sheets
• UC IPM, Agriculture: Tomato Pest Management Guidelines, Tomato Yellow Leaf Curl
• Texas Cooperative Extension, Gardening Fact Sheet: As American as Tomatoes, a History of Tomatoes
• Texas A&M AgriLife Extension, Aggie Horticulture: The Tomato Had To Go Abroad To Make Good
• Purdue Extension FoodLink: Tomato
• Maynard, Donald N & Hochmuth, George J (2007). Knott’s Handbook for Vegetable Growers (5th edition). John Wiley & Sons, Inc.
• Decoteau, Dennis R (2000). Vegetable Crops. Prentice-Hall, Inc.
• Swiader, John M & Ware, George W (2002). Producing Vegetable Crops (5th edition). Interstate Publishers, Inc.
• Sukprakarn, S, Juntakool, S, Huang, R, and Kalb, T (2005). Saving your own vegetable seeds—a guide for farmers. AVRDC publication number 05-647. AVRDC—The World Vegetable Center, Shanhua, Taiwan. 25 pp.
• Seed Savers Exchange, A Guide to Isolation Distances
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853