How Many Plants, and How Far Apart

Two questions decide a growing plan, and they run in opposite directions. How many do I need? comes from what you want to eat. How many fit? comes from geometry. These tools answer both, and the plan is where they meet.

Start with what you want to eat

The How Many Plants to Grow Calculator works backwards from servings rather than forwards from bed space, which is the right direction and the less common one.

Four people, three servings a week, over a 12-week harvest window:

Servings across the window	144
Total harvest wanted	36 lb
Yield per plant	5 lb
Yield per plant after 20% losses	4 lb
Plants to grow	9
Plants if nothing ever failed	8

The loss allowance is the part worth keeping. Eight plants is the arithmetic answer; nine is the answer that survives a slug, a bad transplant and a week of the wrong weather.

The other useful output is the weekly one: 3 lb a week. That is what "36 lb" actually feels like, and it is the number that tells you whether the harvest window is realistic or whether you have designed a glut.

Then find out what fits

The Plant Spacing Calculator turns a bed into a plant count, and it carries one genuinely free improvement.

An 8 × 4 ft bed at 12-inch spacing:

Square rows	32 plants (4 rows of 8)
Offset rows	36 plants

Four extra plants — 12.5% — for no extra space, no extra soil and no closer spacing. Offsetting each row by half a space is the same trick as stacking oranges: a triangular arrangement packs the same circles more tightly than a square grid, while keeping every plant the same distance from its neighbours.

It is the cheapest yield increase in the whole subject, and it costs nothing but laying the rows out differently.

Trees need the geometry doing properly

The Tree Spacing Calculator handles the case where getting it wrong is expensive to fix, because the mistake only becomes visible in about a decade.

Two trees with 20 ft mature canopies:

Distance between trunks	20 ft
Trees along a 100 ft run	6
Distance from a wall	15 ft
Ground each tree gets	400 sq ft
Trees per acre, square grid	109

The trunk spacing is half of each canopy added together — two 20 ft canopies means 10 + 10, so 20 ft apart puts the branch tips just touching.

⚠️ The wall figure is the one people get wrong: 15 ft, not 20. Against a wall you only need half the canopy plus your clearance, because there is no neighbouring tree on that side. Spacing trees from a boundary as though another tree were there wastes a large amount of ground.

Use the mature canopy, not the size at purchase. Everything here is a decision about a tree that does not exist yet, and the cost of underestimating is a decade of crowding followed by removing something you grew for ten years.

Where the two questions meet

Run them in this order:

1. How many do you need? — from servings, with a loss allowance.
2. How many fit? — from bed geometry, offset rows included.
3. Compare. If need exceeds fit, either the harvest window stretches, the bed grows, or the plan changes.

Nine plants needed against 36 that fit is a comfortable plan. The reverse — needing 40 in a bed that holds 32 — is the useful failure, because you found it in February rather than in July.

The through-line

Add a loss allowance	8 plants becomes 9
Offset the rows	32 plants becomes 36
Space trees from a wall	20 ft becomes 15

Three small corrections, all in the direction of getting more from the same ground — and all invisible unless you do the arithmetic before you plant rather than after.

⚠️ Spacing figures assume the mature plant. A bed that looks absurdly empty in May is usually spaced correctly; one that looks right in May is usually crowded by August. Crowded plants compete for light and water and stay damp longer, which is how fungal problems start. Resisting the urge to fill the gaps is most of the skill.