Greenhouse Tomato Fruit Yield ? The Components of Yield
by J Benton Jones, Jr.
Probably no other aspect of greenhouse tomato production is more confusing than what a grower can expect in fruit yield. The fruiting characteristics of greenhouse tomato cultivars are genetically set, although some variation in fruit number, size and weight can be affected by the surrounding plant environment, such as light intensity and duration, and air temperature, humidity and carbon dioxide content. In addition, plant factors, such as plant density, applied cultural practices, mineral nutrition, water status, and freedom from insect and disease infestations are equally influencing factors. Indeterminate tomato cultivars that are normally grown in the greenhouse, are capable of continuous fruit production as long as the plant is adequately maintained. The question is, “what is the potential fruit yield maximum for such tomato cultivars so that a grower can determine the profitability of his greenhouse enterprise as well as judge his growing skill?”
Characteristics of the Components of Fruit Yield
My observation has been that the tomato plant tends to produce a “fixed” fruit yield, a combination of fruit number and weight of each fruit, over a set time period. As fruit numbers increase, fruit weight deceases and vice versa. The number of fruit that a single tomato plant can support at any one time depends on a number of factors. For the production of marketable fruit when growing a beefsteak tomato cultivar, fruit pruning is commonly practiced in order to keep the number of fruit per cluster at no more than three as well as maintaining a “balance” among initially developing fruit, maturing fruit and those reaching maturity for harvest. Leaf pruning is also practiced to keep the plant canopy “open” for greater light penetration.
Recommended Plant Yield Expression
The yield expression method that I recommend is weight of harvested fruit per plant per week. Most greenhouse tomato beefsteak cultivars will generate fruit that range in weight between 6 to 8 ounces with the expectation of harvesting at least 2 fruits per plant per week. Therefore, based on these two fruit yield components, an easily obtained harvest yield of 1 pound of fruit per plant per week requires the harvesting of just two 8 ounce fruit. In addition to the influencing environmental and plant factors mentioned earlier, both fruit number and fruit weight will be also affected by plant spacing.
The percent light interception by the tomato plant canopy measures between 30 to 70% depending on plant spacing. In addition, within row and between row spacing as well as service isle width will determine how much light radiation will impact and penetrate the plant canopy. The recommended area that a single tomato plant occupies within the greenhouse can be as much as 4.5 to as little as 2.0 square feet with plant spacing within the row and between rows ranging from 18 to 30 inches based on the commonly-recommended double-row arrangement of plants.
For greenhouse tomato production under Canadian conditions (1), the optimum space per plant recommended is between 3.7 to 4.3 square feet with row spacing between rows at 31 inches and plant spacing within the row between 13.5 to 15.5 inches with 4 foot isle width. Such plant spacing tends to compensate for the wide range in both light intensity and duration that occurs at high latitudes.
For growing at lower latitudes where light intensities are high but for the winter months, Texas Agricultural Extension Service (2) recommends spacing within the row to obtain a square feet per plant arrangement of 3.1 to 3.4, with 36 inch working aisles between pairs of plant rows spaced no closer than 28 to 30 inches. Mississippi State University Extension Service (3) recommends arranging the plants in double rows that are 4 feet apart on center with 14 to 16 inches between plants.
As mentioned earlier, reducing the area occupied by each plant results in less light penetration into the plant canopy, thereby reducing plant photosynthetic rate that in turn will reduce both the number and size of fruit produced per plant per harvest week. Altering plant positions within the row and between plant rows will open the plant canopy for greater light penetration.
CropKing (4), a major supplier of greenhouses and source of cultural practice procedures for the hydroponic growing of tomatoes, recommends a plant spacing of 4.4 square feet per plant for its 30x128 foot free-standing greenhouse giving a total number of 870 plants in this size structure. For multiple bay greenhouse arrangements, CropKing recommends 3.9 plants per square feet, the total number of plants depending on the area under cover. A 4.0 square foot per plant spacing arrangement is equivalent to 10,857 plants per acre.
Depending on latitude location, most growers will not try to produce a tomato crop either in the low light intensity winter months (December through February) or during the high light intensity summer months (June through August). Therefore, such growers have adopted a two crop cycle production system, a “fall crop” planted in late August harvesting through December and a “spring crop” planted in late February harvesting through June. Employing such a growing system, fruit yield would be expressed as either total fruit weight per area (occupied plant space or entire space) or total fruit weight per plant for each designated “fall” and “spring” crops.
By designing greenhouses that can partially overcome the impact due to periods of low light intensity with the strategic use of supplemented lighting, and then during periods of high light intensity (high air temperatures) with the use of movable shade combined with innovative systems for air cooling, tomato fruit production can be possible year-round. Fruit yield interruption at each plant position can be minimized by employing a plant replacement system that sets a new transplant next to the plant that is to be removed when the transplant begins to set fruit.
The grower’s challenge is how to maintain his crop in order to sustain a fixed fruit yield over the entire harvest period, whether it is an 8 week “fall crop” or a 52 week year-round crop. The best sustained fruit yield for a beefsteak cultivar I have obtained ranged between 1.5 to 2.0 lbs of fruit per plant per week for a spring crop over a 12 week harvest period from the beginning of April through the end of June in a greenhouse located in Athens, Georgia. This high yield was due almost entirely to fruit weight as most of the harvested fruit weighed between 10 to 14 ounces. I attributed this unusual fruit yield to two environmental conditions that existed in the greenhouse, filtered light through trapped water between the two collapsed polyethylene cover sheets and an efficient cross flow air ventilation system that kept air moving through the plant canopy.
The biological fruit yield maximum for greenhouse tomato cultivars is not known. Therefore, the setting of goals by the grower based on obtainable fruit yield potential is not possible. There is need by those who are generating new greenhouse tomato cultivars to begin making that determination
1. Papadopoulos, A.P. 1991. Growing Greenhouse Tomatoes in Soil and Soilless Media. Agricultural Canada Publication 1865/E. 1991.
2. http://aggie-horticulture.tamu.edu/greenhouse/hydroponics/tomato.html. Greenhouse Tomato Culture, Texas Agricultural Extension Service, Texas A&M University System, College Station, Texas.
3. Snyder, R.G. Greenhouse Tomato Handbook. Mississippi State University Extension Service, Publication 1828. Mississippi State University, Mississippi State, MS.
3. CropKing, Inc., 230 Quadral Drive, Wadsworth, OH 44281