What a spacing number actually means
Seed packets and plant labels usually give two figures: the distance between plants in a row, and the distance between rows. In a traditional allotment layout the row gap is wider, leaving room to walk and hoe. In a bed you never step on, you can use the in-row figure in every direction, and that is the basis of this calculator.
Spacing is always measured centre to centre, from the stem of one plant to the stem of the next. The calculator also keeps each plant half a spacing away from the bed edge, so foliage does not spill onto paths and roots are not squeezed against boards.
Square grid or triangular planting?
A square grid lines plants up in neat rows and columns. It is easy to mark out with a string line or a planting board, and easy to hoe between. A triangular or offset layout shifts every other row by half a spacing, so the rows can sit closer together: the gap between rows becomes about 0.87 times the spacing.
In a large bed, the triangular pattern fits roughly 15% more plants at the same spacing, because each plant effectively claims a hexagon of ground instead of a square. In small beds the edges take a bigger share and the gain shrinks, which is why the calculator counts real positions rather than applying a flat percentage.
Square grid
- Quick to mark and easy to follow
- Straight hoeing lanes
- Simple to count and record
- Leaves slightly more unused soil
Triangular
- More plants per square metre
- Canopy closes sooner and shades weeds
- Fiddlier to mark out accurately
- Harder to hoe once plants grow
Typical spacing starting points
Varieties differ widely, so a compact bush tomato and a vigorous cordon type need very different room. Use these ranges as a first guess and adjust to your label.
| Crop | Typical spacing | Notes |
|---|---|---|
| Carrot, radish | 5–8 cm | Usually sown thinly, then thinned |
| Onion sets, beetroot | 10 cm | Closer spacing gives smaller bulbs and roots |
| Bush beans, spinach | 15–20 cm | Good for succession sowing |
| Lettuce, basil | 20–30 cm | Cut-and-come-again leaves can go closer |
| Strawberry | 30–45 cm | Runners fill gaps over time |
| Pepper, kale, cabbage | 40–60 cm | Larger brassicas prefer the wider end |
| Tomato | 45–60 cm | Bush types sprawl and need more room |
| Courgette, squash | 90 cm or more | Trailing types can take several square metres |
Intensive planting: when tighter helps and when it backfires
Tighter spacing covers the soil faster, shades out weed seedlings and squeezes more harvest from a small plot. It works well for leafy crops picked young, and in rich soil with steady watering.
It backfires when plants compete for water and nutrients in poor soil, or when crowded leaves stay damp. Tomatoes, courgettes and squash in particular suffer when airflow is poor, as fungal problems spread more easily through a dense, humid canopy. If disease has been a problem before, give those crops the wider end of their range.
Why the calculator adds spares
Not every seed germinates, and slugs, birds and cold snaps take their share of young plants. Raising around ten percent extra lets you fill gaps quickly with plants of the same age, so the bed matures evenly. Any leftovers make welcome gifts for neighbours.
Common spacing mistakes
- Using the row spacing in both directions inside a bed, which wastes space.
- Planting right up to the edge, so leaves hang over paths.
- Forgetting that tall crops shade their neighbours.
- Spacing for tiny seedlings instead of the mature plant.