Nursery plants are costly to produce. Each plant represents an investment of labor and materials as well as heat, water, and other cultural expenses. Growers must determine the total number of plants needed in the size required at the time of harvest. For some growers, the harvested crop is ready to be planted in homeowners’ yards. For other growers, the harvested crop is young grafts or liners that will be further grown by another nursery that has chosen not to do its own propagating.
Profits are lost when an excess of plants is produced and cannot be sold. They are also lost when too few plants are ready when needed. Growers attempt to anticipate and allow for losses due to mortality during production, failure to meet grading standards, and replacements required for buyer rejections.
The number of plants grown is calculated by working backward from the desired harvest quota. The technique is adaptable to all phases of nursery production regardless of whether the nursery specializes in propagation, wholesale field production, or container production. The formula is a simple one:
Number of plants necessary to start =
The production quota ^
The estimated return percentage where the estimated return percentage =
(100%—the percent mortality)
Example 1: If a production quota (representing 100 percent of the crop) required 5,000 trees for a landscape installation on a certain date, and the landscape contractor traditionally rejected 10 percent of the plants on first inspection, insisting on replacements, the nursery grower would calculate the number of plants to be grown to harvest size as follows.
Number of trees to be grown = 5,000 trees ^ (100% – 10%)
= 5,000 trees ^ .90 = 5,556 trees
Example 2: To calculate the number of young trees to plant in the field several years in advance of the harvest, the grower first estimates at 15 percent the percentage of loss due to insects, diseases, rodents, equipment injury, or environmental damage. The formula is then applied again, using 5,556 trees as the production quota.
Number of saplings to install in the field = 5,556 trees ^ (100% – 15%)
= 5,556 trees ^ .85 = 6,537 trees
In a similar manner, the grower could work backward to calculate the number of field liners needed to produce the saplings, then the number of seedlings or grafts required to produce the liners.