How many bulbs do I need per square metre?

On a square grid the number per square metre is 100 divided by the spacing in centimetres, squared. At 12 cm spacing that is about 69 bulbs per square metre, at 10 cm about 100, and at 15 cm about 44. Multiply by your bed area in square metres for the total, then round up so you have a few spare.

Should I plant bulbs in a grid or naturally?

A grid gives a formal, even display and is easy to plan, which is what this calculator assumes. For a natural drift, scatter the same number of bulbs by hand and plant them where they land. A triangular or staggered layout fits roughly 15 percent more bulbs into the same area than a square grid at the same spacing.

Bulb Spacing Calculator

This bulb spacing calculator tells you how many flower bulbs to buy and plant to fill a bed at the spacing you want. Enter the length and width of the bed and the spacing you plan to leave between bulbs, and it returns the number of bulbs needed, the planting density per square metre, and the bed area, so you can order the right quantity and not end up short halfway through planting or with a box of leftovers. The right spacing depends on the bulb: tulips and daffodils usually go about 10 to 15 cm apart, small bulbs like crocus and grape hyacinth around 5 to 8 cm, and big alliums 20 cm or more, with closer spacing giving a fuller show in the first season. The defaults fill a 2 metre by 1 metre bed with bulbs 12 cm apart, which works out at close to 70 bulbs per square metre and around 139 bulbs in total. The calculator assumes an even square grid, which is easy to plan and mark out. If you want a more natural drift, order the same number and scatter them by hand, and remember a staggered or triangular layout fits roughly 15 percent more bulbs into the same area at the same spacing. It always rounds the total up, so you plant the whole bed with a few bulbs to spare. Use it for tulips, daffodils, crocus and any bulb planted on a regular spacing.

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Bed length

Bed width

Spacing between bulbs

139

flower bulbs to plant (rounded up)

Bed area2.0 m²

Bulbs per square metre69.4

At spacing12 cm

Assumes an even square grid. A staggered or triangular layout fits about 15 percent more bulbs at the same spacing. The total is rounded up so the bed is fully planted. Estimate only.

How it works

The bed area is the length times the width in metres. On a square grid the number of bulbs per square metre is 100 divided by the spacing in centimetres, squared, because each bulb takes up a spacing by spacing square. Multiply that density by the bed area to get the total, then round up so the bed is fully covered. Halving the spacing does not double the bulbs needed, it roughly quadruples them, since the density depends on the spacing squared, which is worth knowing before you order.

Worked example

Take a 2 metre by 1 metre bed with bulbs 12 cm apart. The area is 2 square metres. The density is 100 divided by 12, which is 8.33, squared, about 69.4 bulbs per square metre. Multiply by the 2 square metre area for 138.9, which rounds up to 139 bulbs. Widen the spacing to 15 cm and the density drops to about 44 per square metre, needing only 89 bulbs for the same bed.

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