The spacing of a greenhouse crop has a direct impact on the costs of production and the quality of the crop. Closer spacing permits more plants to be grown, but if it is too close, it reduces the quality of the product. Spacing that is too great produces excellent plants but at the expense of crop numbers and profit.
Different methods of growing require different techniques of spacing. With bench crop production, the spacing decision made at the time of planting remains unchanged throughout the life of the crop. Potted crop production can be the same, with no movement of the pots after planting (termed fixed spacing); or the crop can be started in small pots with close spacing, and both container size and spacing can be increased as the crop matures (termed expanding spacing). For example, the crop may be started in three-inch pots and advance through several transplantings to mature size in six-inch pots. Each transplanting requires labor and more space. The space can only be provided by moving out some other crop. When certain holidays fall close together, such as Valentine’s Day and Easter or Easter and Mother’s Day, there may not be enough time to space out the next crop before damage is done due to close spacing. Expanding spacing is commonly practiced, though, and probably will continue to be. Expanding and fixed spacing are compared and summarized in Table 20-2.
Whether spacing bench crops or potted plants, the objectives are the same. The plants must receive adequate sunlight and air to permit photosynthesis to proceed unimpaired. Crowded spacing can reduce photosynthesis and increase the possibility of disease due to shaded, overly moist foliage and reduced air circulation. Where expanding spacing is used, the dates of repotting and spacing must be part of the production schedule for each crop. Consideration must also be given to future crops. As the current crop reaches maturity, its time of sale must be anticipated to permit the wider spacing of another crop.
A Comparison of Expanding and Fixed Spacing
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Expanding Spacing |
Fixed Spacing |
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• Plants are transplanted one or more times |
• Plants are not transplanted |
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• Several production containers are required per plant |
• A single production container is required per plant |
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• More labor is required |
• Less labor is required |
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• Less bench space is required at the beginning. Other crops in later stages of maturity can also be grown |
• Greater bench space is required at the beginning, which may limit the number of other plants grown annually |
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• Roots often develop better when pots are not larger than the plant needs |
• Early root development may be limited with small plants in large pots |
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• Small pots dry out more quickly |
• Large pots do not dry out as quickly |
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• Plants can be damaged if repotting or increased spacing is delayed |
• Certain crops, such as bulbous flowers, do not transplant well and require fixed spacing |
figure 20-9. Two methods of labeling crops on a greenhouse bench: A bench crop is identified on the outside end. A pot crop is identified on the pot closest to the front and left side. (Delmar/Cengage Learning)
Labeling the crop is the means of identifying the plants on the bench. It is necessary where different varieties of similar plants are grown, since they often cannot be identified otherwise until they flower. Chrysanthemums and geraniums are two common examples, but exotic orchids are just as easily confused when only the foliage is visible.
Bench crops are often labeled on the end of the bench when a single variety is being grown. Potted crops may be labeled on each container, especially if the crop is protected by a patent. These labels are furnished by the propagator supplier. Other potted crops are not individually labeled. Instead the pot closest to the front and the left side of the bench is labeled. All plants spaced behind and to the right are the same variety until the next label marks the next variety (Figure 20-9). In addition to the variety name, the label may contain information such as the flower color, date of planting, and date of harvest.
