Thinking About Greenhouse Tomatoes?

January 10, 2001 - 01:00

Like any other greenhouse crop, growing greenhouse tomatoes is more than just planting some seeds and raking in the money. Here are a few suggestions to get you on your way.

The production of greenhouse vegetables can be a lucrative business for the greenhouse grower who wants to diversify his or her business. Most greenhouse vegetables in the United States are raised hydroponically, i.e., without soil, but some growers do grow plants in the ground. Of all the possible vegetables that can be grown in a greenhouse, and there are many possibilities, tomatoes are by far the most widely grown. This is due to both the market demand (everybody likes tomatoes) and to the better availability of technical information for tomatoes.

Worldwide, other vegetables grown in greenhouses include cucumbers, peppers, lettuce, eggplant, spinach, melons, various herbs and other specialty crops. Some fruit crops — for example, strawberries and raspberries — are also well-suited to hydroponics. While you can grow many crops using hydroponic methods, it is important to remember the marketability of the crop. If a crop does not have a strong market in your geographic region, sales will be weak. In the United States in general, tomatoes have the strongest market demand; therefore, they are the best choice of greenhouse vegetable crops for most regions of the country.

Before breaking ground for a new greenhouse, however, you must understand the major time commitment and amount of work involved with greenhouse tomatoes. In fact, the time and effort required to raise greenhouse tomatoes is more similar to a dairy or poultry operation than to any field-grown vegetable or fruit crop because the grower needs to be present for daily responsibilities and chores. Leaving the tomato plants alone for a day or two without care could lead to a crop loss.

Large corporate owners with 20 or more acres in greenhouse tomato production constitute about half of all the greenhouse tomato acreage in the United States. Numerically, however, most of the growers in this country are quite small, with less than 10,000 square feet of floor space each. For example, in Mississippi, the average greenhouse tomato grower has 2.4 free-standing or gutter-connected bays, totaling about 6,000 square feet.

Greenhouse tomato acreage has been on the rise since the mid 1990s. Much of the expansion is explained by a changing consumer preference toward the best quality vegetables. Greenhouse tomatoes are harvested vine ripened, or at least well on the way to a red color stage, to ensure good flavor. Tomatoes grown under controlled greenhouse conditions are more uniform in size, shape and color and have a better resistance to diseases than do field-grown tomatoes. In many urban areas, consumers are not concerned with the higher price of greenhouse tomatoes, since they get quality in return. Greenhouse tomatoes are never picked green and gassed with ethylene to promote ripening, a common practice of field-grown winter tomatoes in the extreme southern United States, Mexico and Central America.

The information database for greenhouse tomatoes is small when compared to field vegetables, often making it difficult to obtain assistance from county extension agents or other trained personnel. The prospective grower, therefore, must be well prepared in advance by obtaining and reading publications, attending short courses and seminars, and visiting other growers to learn from their experiences.

Variety Selection

The best advice for selecting the type of tomatoes you’d like to grow is to choose the best variety on the market. Your crop’s potential will be limited if you choose an inferior variety. While the cost of high quality hybrid seed is not low (20 to 25 cents per seed, depending on quantity), it is still one of the best investments for the dollar that a grower can make. Selection of variety is based on fruit type (beefsteak or "beef", cocktail, cherry, cluster, roma, plum, etc.), color (red or pink), fruit size, disease resistance and potential for physiological disorders (catfacing, blossom-end rot, russetting, etc).

The quality of tomato varieties has risen sharply in the past 10 years due to the breeders at commercial seed companies producing better varieties. Now, we have varieties that are higher yielding, more uniform in size and shape, less prone to several physiological disorders and highly disease resistant. In the past few years, breeders have added resistance to Cladosporium leaf mold (C5) and Fusarium Crown and Root Rot (FR) to newer varieties.

The most widely used tomato variety in the United States now is ‘Trust’, with about 85 percent of the market, but there are several new varieties showing promise. Use of outdoor varieties by commercial greenhouse growers is a mistake. Such varieties may be excellent in the garden, but they will not perform as well in the greenhouse as varieties that have been bred for this purpose.

Tools of the Trade

In order to profitably grow a crop of greenhouse tomatoes, a grower needs to have and use both a pH meter and an EC meter. The pH meter is needed to ensure that the nutrient solution pH is in the range of 5.6 to 5.8 for tomatoes grown in aggregate media. The electroconductivity (EC) meter is used to make sure that the level of fertilizer dissolved in the water remains between 1.0 and 3.0 millimhos or between 1,000 and 3,000 micromhos. Each time a new batch of nutrient solution is mixed, the EC and pH should be checked to detect mistakes before dispersing the solution to plants. Keeping track of pH and EC is the first step in managing the greenhouse tomato nutrition program.

Pollination

Tomatoes in the greenhouse need to be pollinated. Outdoor tomatoes rely on wind for most pollination, but in the greenhouse, wind from ventilation is inadequate to achieve good pollination.

The best ways to pollinate greenhouse tomatoes are either with an electric pollinator or with the assistance of bumblebees. Pollinators are available from greenhouse suppliers. Manual pollination needs to be done every other day, preferably around mid-day, when the relative humidity is lowest.

There are other means of pollinating (leaf blower, electric toothbrush, hitting strings with sticks, etc.), but nothing (other than bumble bees) is as effective as a good electric pollinator. Rechargeable batteries are recommended, since these can be charged after each use and are ready when needed. Bumblebees have been shown to be very effective pollinators and are recommended for all growers with more than 10,000 square feet under one roof, and some growers with 5,000 to 10,000 square feet if labor is either too expensive or unavailable.

Growers need to start pollinating as soon as the first flower opens. Pollinate every cluster on each plant that has open flowers. Touch the pollinator wand to the top of the pedicel, not to each individual blossom. Touching the blossom can damage the young ovary, causing fruit with holes in the sides and other deformations, or even knocking off flowers.

The newest trend in pollination is the prevalence of bumblebees. This is mostly due to the large size of many newer greenhouse ranges. To pollinate 10 or 20 acres by hand would be too time consuming and expensive. Larger growers have come to depend on bumblebees to get the pollinating job done for them. Bumblebee hives are available for purchase from several greenhouse supply companies. For smaller growers, the hand pollinator is still more cost effective, although more laborious.

Things to Know Before You Grow

To determine how many plants can be grown in a greenhouse, multiply the greenhouse length by the width and divide by four. This is because each tomato plant needs at least four square feet. Planting at a higher density will not give more yield per greenhouse, because the yield per plant will be lower. Do not include floor space that is used for packing benches, bulk fertilizer tanks, work areas, sales areas, etc., in this calculation. Subtract such areas from the square footage before dividing by four.

There should be no smoking in or near the greenhouse. Tobacco carries tobacco mosaic virus (TMV) which can be transmitted on the hands of smokers, chewers, snuffers, etc.

Keep good records. The following information about the crop should be recorded in a notebook: planting and harvest dates; spray dates; spray materials; amount of each fertilizer applied and when changes are made; daily pH and EC; dates crop is seeded, transplanted, topped and terminated; and observations of anything unusual with the crop — deficiency symptoms, physiological disorders, diseases, occurrence of insects, etc.

Artificial lighting is not economically feasible with greenhouse tomatoes (except, perhaps, in the single cluster system). The cost of high intensity lamps and the electricity to power them would not be balanced by higher yield to pay for the extra expense.

There is no magic to growing a good crop. The key is good management, and good management is just making the right decisions at the right time.

The biggest reason for failure in this business is starting too big. There are so many things to learn about growing greenhouse tomatoes that it is best to start with one greenhouse. Later, a grower can expand to as large an operation as desired. But making "new grower mistakes" on several bays at once is too costly, and may make it impossible to make payments on a sizeable loan.

Before actually investing in a greenhouse tomato operation, you must be certain that there is a market for your produce. Once in business, your state extension specialist and local county agent should be contacted for assistance with questions and problems.

Where To Find More Information

For more information on greenhouse tomatoes, visit the Greenhouse Tomato FAQ Web site at ext.msstate.edu/anr/

plantsoil/vegfruit/tomato/ghtomato/faq.html. In addition to many frequently asked questions, it has links to entire documents on production and pest management, and a comprehensive list of other Web sites that should provide valuable information.

Attending short courses that are geared specifically toward greenhouse tomato production is another excellent way to learn a lot about this crop. There are state greenhouse vegetable programs each year in Florida, Mississippi, New Jersey, North Carolina and Texas. Also, The Ohio Short Course will have a greenhouse vegetable session in its conference schedule for 2001. It is well worth the expense to travel to a short course in another state to learn as much as possible about production techniques and potential problems.

About The Author

Rick Snyder is an extension vegetable specialist at the Truck Crops Experiment Station, Mississippi State University, Crystal Springs, Miss. He can be reached via email at RickS@ext.msstate.edu

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