The crop shrinks and the footprint grows
Two things happen on the way from a cutting to a saleable plant, and they pull in opposite directions. The count falls, because not everything roots and not everything grades out. The area per plant rises, because a plant that fitted a 2.5 inch cell ends up in a can that needs 14 inch centres. The area is the product of those two, and the spacing wins by a wide margin.
On the figures the form opens with, 10,000 cuttings at 2.5 inch centres on an offset layout occupy 5.4 square inches each, which is 376 square feet of plants and 470 square feet of ground once a quarter is added for access. Eight thousand survivors in 1 gallon cans at 8 inch centres occupy 55.4 square inches each: 3,079 square feet of plants, 3,849 of ground. Seven thousand three hundred and sixty of those in 3 gallon cans at 14 inch centres occupy 169.7 square inches each: 8,676 square feet of plants, 10,845 of ground. The crop lost 26 percent of its plants between the first stage and the third, and its footprint grew 23.1 times over.
| Stage | Plants held | Sq in each | Plant area | Ground, +25% |
|---|---|---|---|---|
| Liner, 2.5 in centres | 10,000 | 5.4 | 376 sq ft | 470 sq ft |
| 1 gallon, 8 in centres | 8,000 | 55.4 | 3,079 sq ft | 3,849 sq ft |
| 3 gallon, 14 in centres | 7,360 | 169.7 | 8,676 sq ft | 10,845 sq ft |
That is the teaching point of this page and it is worth stating flatly: a crop takes its space at the end of the run, not at the beginning. Whatever you build for the sticking bench is irrelevant to how much land the crop needs. Size the yard on the last pot-up.
When the peak is not at the end
The calculator computes which stage peaks rather than assuming the last one, because it is not always the last one. Area at a stage is the plants held times the square of the spacing times a pattern factor. Going from one stage to the next multiplies the area by the survival share and by the ratio of the spacings squared. The peak moves earlier only when a transition loses more than the spacing gains, which needs a very heavy loss: stepping from 8 inch to 14 inch centres multiplies area by 3.06 before survival, so it takes a survival share of 32 percent or less at that transition before the footprint shrinks, which is where the calculator actually moves the peak off the last stage. If your own figures put the peak anywhere but the last stage, look hard at the survival number you typed, because it is doing something unusual.
Media follows the same shape
Media is worse, because container volume goes up faster than spacing does. At 82 percent of trade size and a 90 percent fill, a 0.07 gallon liner takes 11.9 cubic inches, a 1 gallon can takes 170.5, and a 3 gallon takes 511.4. Across the run that is 69.1 cubic feet, 789.2 cubic feet and 2,178.3 cubic feet — 3,036.6 cubic feet altogether, or 112.47 cubic yards, with 71.7 percent of it going into the final stage alone.
The two percentages that drive that are the trade-size share and the fill, and both deserve measuring rather than guessing. A container sold as three gallons commonly holds well under three gallons of water, and the difference lands straight on the media invoice. Measure one with a jug. If you want the per-container volume from a measured pot rather than a trade size, the growing media and container volume calculator takes diameters and heights and gives cubic feet, bags and wet weight. For a single repot rather than a crop, pot size step-up handles the root ball displacement this page ignores.
Square foot weeks
The last section multiplies each stage area by the weeks held and adds them up. On the defaults that is 470 by 8, 3,849 by 20 and 10,845 by 26, which comes to 362,697 square foot weeks for 6,992 saleable plants, or 51.9 square foot weeks each. It is an awkward unit and a very useful one, because it is the thing a nursery actually sells: occupancy of covered or irrigated ground, over time. Put a price per square foot per week on it and you have the space line of a cost per plant, which is what the cost per plant calculator does.
Nothing on this page knows what you are growing. The survival shares, the spacings, the container sizes and the weeks are all yours, taken from your own records or from whatever propagation reference or extension service you work with. No figure here is a recommendation, and the page issues no verdict about whether any of it will work.
Questions people ask
Is the survival percentage applied on the way in or the way out of a stage?
On the way out. A stage holds the number that arrived, uses the media and ground for that number, and then the share you entered moves on to the next stage. So stage one holds all 10,000 cuttings and takes media and space for 10,000, and only 8,000 arrive at stage two. That is the conservative order and it matches how the losses actually happen — you have already potted and watered the ones that later fail.
Why is offset spacing the default rather than a square grid?
Because it fits more in the same area and most container yards are set out that way. An offset layout gives each plant a hexagon of area rather than a square, which is the square of the spacing times 0.866. That is 13.4 percent less ground for the same centre distance. On the default third stage that is the difference between 10,845 and 12,522 square feet of ground, or about four hundredths of an acre. Both options are there because some operations pot into rows against a drip header and cannot offset.
What should I put in the aisle and edge allowance?
Whatever your layout actually needs, measured off a block you already have. It covers access lanes between blocks, the run for a drip header, turning space at the ends and the strip along a fence that never quite gets used. Twenty-five percent is the placeholder in the form and nothing more than that. Measure a block you know: divide its fenced area by the plant area you computed from its spacing, and the difference is your real overhead.
Can I use this for a crop that skips a stage or goes straight into a finished can?
Yes. Fill in only the stages you use and leave the rest blank; the calculator ignores any stage without a container size and a spacing. A single stage works fine and gives you media and ground for one block. Two stages cover a straight liner-to-finish crop. The peak logic still runs, and with one stage the peak is trivially that stage.
Does the page account for plants that are moved out and spaced part way through a stage?
No, and that is a real limitation. A crop that goes into cans pot-to-pot and is spaced out six weeks later occupies two quite different areas within one stage, and this page charges the whole stage at one spacing. The workaround is to split it into two stages with the same container size, the same trade size share, different spacings and different weeks. The media line will then double-count the container, so set the second one to a container size of the smallest value the field accepts and read only its area and its square foot weeks.