From a Blank Bed to the Right Seed Count

Spacing is the harvest plan hiding in plain sight

Every packet quotes a spacing, and every gardener secretly ignores a few. Too tight buys trouble: plants compete for light and root room, salads never fill out, roots stay thin, and damp crowded leaves invite rot. Too loose wastes the most expensive thing you own in this system, the bed area.

The geometry is honest once you see it. A plant at 30 centimetres spacing claims a square of that size. That is 0.09 of a square metre, so a square metre holds about eleven of them. Multiply by the area and the bed's capacity appears, no guessing involved.

That capacity number is the whole planning hinge. Harvest estimates hang on it. Eleven courgettes per square metre would be a compost problem; one per square metre is the truth the 90-centimetre spacing encodes. Seed buying, meal sizing and preserving all inherit from the plant count.

The quiet trap is treating spacing as a minimum rather than a claim. The tight figure suits one season's cutting lettuce, harvested young. The generous figure suits a full head, a full root, a full plant. The calculator takes one number and asks you to mean it.

• Spacing squared is the area each plant claims. Divide the bed by it, honestly.
• Packet minimums suit quick harvests; the generous figure suits full-size crops.
• Plant count drives everything downstream: harvests, gluts, freezer space.

Block planting, and why the maths uses squares

The calculator assumes plants spread evenly across the bed in a grid, the block-planting method that intensive beds are built around. Wide rows with paths between them waste the area the frame was built to farm, and block planting is the standard raised-bed answer.

A grid is the simplest honest model. Real gardens stagger the pattern or scatter seed, and staggered rows squeeze a few more plants into the same area. The grid figure is therefore a sound floor rather than a ceiling, which is the right direction for planning.

The 10,000-over-spacing-squared formula lands close to the old intensive rule of thumb that a bed's plant count equals its area times a per-crop density. What it adds is the ability to bend the density with your own spacing decision, per season, per bed.

One geometry note for odd shapes: enter the productive area, not the shape's romantic outline. A keyhole bed's path is walking room, not carrot soil. Measure the part roots can claim and let the number be smaller than the drawing looks.

Germination is a percentage, so sow for the odds

Packet germination rates are promises made under ideal lab conditions. Fresh, cool-stored seed often meets them. A two-year-old packet from a warm shed may beat half of them. The calculator's wager input turns that reality into seed counts.

The conversion is deliberately blunt: plants wanted, divided by the germination share. Eighty-five percent and forty lettuces need about forty-seven seeds. Seventy percent and the same forty need fifty-seven, and old carrot seed has no shame about asking for more.

Sowing extra is not waste; it is the thinning plan. The surplus seeds are the insurance that still gives a full stand. The extra seedlings pulled at thinnings become the first salad of the season. Gardeners who sow exact counts garden against their own odds.

For expensive or large seed, beans and squashes, flip the habit: pre-sprout on damp paper and plant only the seeds that have clearly chitted. The germination wager shrinks toward certainty, and the calculator's seed total becomes a shopping list rather than a scatter.

Succession sowings: multiplying one bed across the season

One sowing gives one harvest window, then the bed sits idle exactly when the kitchen still needs it. Succession sowing splits the season into rounds. The calculator multiplies the seed total by each round you plan, because every round needs its own wager.

The rhythm beats the arithmetic for most crops: a short row or half a tray every fortnight instead of forty lettuces on one April Sunday. The same total seed, spread, produces a continuous harvest instead of a glut and a famine.

Round spacing is the planning partner here. The crop's days to maturity decide whether fortnight intervals stack or overlap. The bed's turnaround time decides whether round three is lettuce again or the start of the winter sowing. The site's blog pages on planting timing cover the calendar detail.

Fast crops reward the most rounds: radishes at three weeks can run five or six successions in the season one broccoli occupies. Slow crops punish false starts: a courgette round sowing three weeks late simply never pays rent. The rounds input is a strategy dial, not a seed multiplier alone.

Assumptions, limits, and the judgement left to you

The model counts full-size plants in one shared bed. Intercropping, squeezing a quick catch crop between slow ones, lets two crops share the same square metres. That practice lands outside the single-spacing assumption. Plan the main crop with this tool, then tuck fast crops into its gaps.

Some crops defy the grid honestly. Broad beans and tulips want a line, onions dislike crowding at the bulb, and pumpkins run across paths into soil the calculator cannot see. For those, divide the area by the hill or vine footprint rather than the spacing square. Or simply count plants and back-solve the area they need.

The packet's seed count is the softest input. Bulk and saved seed vary wildly, and a carrot packet's eight hundred seeds can be a lucky box or a stale one. Weigh counts from your own packets when precision matters, and let the rest stay within ten percent.

Finally, the calculator never questions whether forty plants will be eaten. Surplus at the fence is a well-known garden outcome. Size the plant count by the household's true appetite, which the harvest and preserving planners here can help you cross-check against freezer and shelf space.