Flower Bulb Calculator
How many tulip, daffodil, crocus, allium or dahlia bulbs do you need? Enter the bed size to get the number of bulbs, planting depth, spacing and the season to plant — metric or US.
How it works
bulbs = bed area ÷ spacing² (bulbs per m² = 10,000 ÷ spacing in cm²; per sq ft = 144 ÷ spacing in inches²) · depth ≈ 2–3 × bulb height
The Royal Horticultural Society and university extension services give the same rule for spring-flowering bulbs: plant at two to three times the bulb’s own height deep, and space bulbs about two bulb-widths apart — closer for a dense, full display. The calculator uses typical depths and spacings for each bulb (for example tulips and daffodils 15 cm deep and 12 cm apart, crocus and snowdrops 8 cm deep and 8 cm apart) on a square grid. Hardy spring bulbs go in during autumn, 6–8 weeks before the ground freezes; summer bulbs such as gladiolus and dahlias are planted in spring after the last frost.
Worked example
A 2 m × 1 m bed of tulips spaced 12 cm apart: 10,000 ÷ 12² = 69.4 bulbs per m², and 2 m² × 69.4 = 138.9, so buy 139 bulbs and plant them 15 cm deep in autumn.
Sources: RHS — Bulbs: planting · University of Minnesota Extension — Planting bulbs
Frequently asked questions
How many tulip bulbs per square metre?
About 50–100 depending on the look: 70 at 12 cm spacing is a full display, 100 at 10 cm a dense one. Per square foot that is roughly 5–9 bulbs.
How deep do you plant bulbs?
Two to three times the height of the bulb: about 15 cm (6″) for tulips, daffodils and hyacinths, 8 cm (3″) for crocus, snowdrops and grape hyacinths, and up to 20 cm (8″) for lilies. In light sandy soil plant a little deeper.
When should I plant spring bulbs?
In autumn, when the soil has cooled to below about 13 °C (55 °F) — typically September–October for daffodils and October–November for tulips in temperate climates — so they can root before winter.
Should I plant bulbs in rows or clusters?
Clusters or drifts look more natural than straight rows. Plant groups of 7–15 bulbs of one kind, or layer several kinds in the same hole (“lasagna planting”) for a longer display.
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This calculator is for educational purposes. Double-check important results before acting on them.