Bulb Spacing Calculator
Plan a bulb bed like a horticulturist: choose your bulb type, enter the bed size, and get the exact planting distance, planting depth, and how many bulbs to buy — in a square grid or a space-saving staggered layout. Spacing and depth figures come from published horticultural references (see methodology), not guesswork.
Your planting plan
Worked examples
Bulb spacing & depth reference table
Default spacing used by the calculator is the midpoint of each published range. Depth is measured from the bottom of the bulb to the soil surface.
| Bulb | Spacing | Depth |
|---|---|---|
| Tulip Tulipa spp. | 10–15 cm (3.9–5.9 in) | 15 cm (5.9 in) |
| Daffodil / Narcissus Narcissus spp. | 10–15 cm (3.9–5.9 in) | 15 cm (5.9 in) |
| Hyacinth Hyacinthus orientalis | 10–15 cm (3.9–5.9 in) | 13 cm (5.1 in) |
| Crocus Crocus spp. | 8 cm (3.1 in) | 8 cm (3.1 in) |
| Grape hyacinth Muscari spp. | 5–8 cm (2–3.1 in) | 8 cm (3.1 in) |
| Snowdrop Galanthus spp. | 8 cm (3.1 in) | 8 cm (3.1 in) |
| Ornamental onion (large) Allium giganteum / 'Globemaster' | 20–30 cm (7.9–11.8 in) | 18 cm (7.1 in) |
| Lily (Asiatic/Oriental) Lilium spp. | 20–30 cm (7.9–11.8 in) | 18 cm (7.1 in) |
| Gladiolus Gladiolus x hortulanus | 10–15 cm (3.9–5.9 in) | 12 cm (4.7 in) |
| Freesia Freesia x hybrida | 5–8 cm (2–3.1 in) | 5 cm (2 in) |
| Anemone Anemone blanda / coronaria | 8–10 cm (3.1–3.9 in) | 6 cm (2.4 in) |
| Ranunculus Ranunculus asiaticus | 10 cm (3.9 in) | 5 cm (2 in) |
| Dutch iris Iris x hollandica | 8 cm (3.1 in) | 13 cm (5.1 in) |
| Dahlia (tuber) Dahlia spp. | 45–60 cm (17.7–23.6 in) | 12 cm (4.7 in) |
| Tuberous begonia Begonia x tuberhybrida | 20–30 cm (7.9–11.8 in) | 2.5 cm (1 in) |
| Canna Canna indica | 30–45 cm (11.8–17.7 in) | 12 cm (4.7 in) |
| Garlic (cloves) Allium sativum | 8–15 cm (3.1–5.9 in) | 6 cm (2.4 in) |
| Onion sets Allium cepa (sets) | 5–10 cm (2–3.9 in) | 2 cm (0.8 in) |
Methodology & sources
- Spacing ranges and depths are taken from published horticultural charts, primarily the Gardening Know How bulb chart (depth measured bottom-of-bulb to surface) and Horticulture Magazine's planting-depths guide.
- Garlic and onion figures follow the LSU AgCenter: garlic cloves 2–3 in deep, 3–6 in apart; bulb-forming onion transplants 2–4 in apart, base 0.5–0.75 in deep.
- Default spacing = midpoint of each published range (documented, e.g. tulips 10–15 cm → 12.5 cm). The calculator shows the full range so you can plant tighter for drifts or wider for permanent plantings.
- General depth rule (RHS): plant bulbs 2–3× their own height; lilies and large alliums sit at the deep end of this rule.
- Grid math: bulbs per row = ⌊width ÷ spacing⌋, rows = ⌊length ÷ spacing⌋, first bulb one full spacing in from the edge. Staggered math: alternate rows offset by half a spacing, row pitch = spacing × √3/2 ≈ 0.866 × spacing.
- Sources: Gardening Know How — Planting Bulbs; Horticulture Magazine — Bulb Planting Depths; Horticulture Magazine — Bulb Calculator; LSU AgCenter — Garlic and Bulb Onions; gardeningetc — RHS bulb guidance.
Frequently asked questions
How many tulip bulbs do I need for a 1 m x 2 m bed?
128 tulip bulbs in a square grid layout (8 columns x 16 rows) at the calculator's default 12.5 cm spacing, planted 15 cm deep. Switch to the staggered (triangular) layout and the same bed holds 135 bulbs.
How far apart should tulip bulbs be planted?
Published guidance is 10 to 15 cm apart (4 to 6 inches), and this calculator uses the midpoint, 12.5 cm (about 4.9 in), as its default. Plant closer within that range for a denser drift display, wider for bulbs you plan to leave undisturbed for years.
How deep should tulip bulbs be planted?
15 cm deep (about 6 in), measured from the bottom of the bulb to the soil surface. The Royal Horticultural Society's general rule is to plant bulbs 2 to 3 times their own height; tulips follow the deeper end of that rule.
How many daffodil bulbs fit in a 2 m x 3 m bed?
384 daffodil bulbs in a square grid (16 columns x 24 rows) at 12.5 cm spacing, planted 15 cm deep. That is 64 bulbs per square metre.
How many crocus bulbs do I need for a 4 ft x 8 ft bed?
450 crocus bulbs in a square grid (15 columns x 30 rows) at 8 cm (about 3.1 in) spacing, planted 8 cm deep. Small bulbs like crocus pack roughly 151 per square metre at grid spacing.
How deep and how far apart should garlic cloves be planted?
Plant garlic cloves 6 cm deep (about 2.4 in) and 11.5 cm apart (about 4.5 in) by default, within the LSU AgCenter's published range of 2 to 3 inches deep and 3 to 6 inches apart. Point the tip upward.
What is a staggered (triangular) planting layout?
Rows are offset by half a spacing so bulbs sit in a triangular pattern instead of a square grid, with rows about 0.866 x spacing apart. It fits roughly 5 to 8% more bulbs: a 1 m x 2 m tulip bed goes from 128 bulbs in grid layout to 135 staggered.
How do I calculate how long a bed must be for a set number of bulbs?
Use reverse mode: enter the bulb count and bed width. For example, 128 tulip bulbs in a 1 m wide bed in grid layout need a bed exactly 200 cm (2 m) long. The calculator rounds up to whole rows, so 50 daffodil bulbs in a 2 m wide bed in staggered layout need about 45.0 cm.
Is planting depth measured from the top or bottom of the bulb?
From the bottom of the bulb to the soil surface. That is the convention used by the published charts this calculator follows, and the one the planting-depth column in the bulb table below uses.
Is spacing measured centre to centre?
Yes. Spacing here means centre-to-centre distance between bulbs, with the first bulb placed one full spacing in from the bed edge, so no bulb is ever centred right against the border on the starting side.
How many bulbs per square metre should I buy?
At grid spacing it is simply 10,000 divided by the square of the spacing in cm. Tulips at 12.5 cm give 64 bulbs per square metre; muscari at 6.5 cm give 196 per square metre. The calculator shows this figure for every result.
How far apart and how deep should onion sets be planted?
Onion sets default to 7.5 cm apart (published range 5 to 10 cm) and 2 cm deep, matching the LSU AgCenter guidance of 2 to 4 inches apart with the base of the transplant 0.5 to 0.75 inch deep. Sixty onion sets in a 1 m wide bed need a bed 37.5 cm long.
How many dahlia tubers fit in a 2 m x 2 m bed?
9 dahlia tubers in a 3 x 3 grid at the default 52.5 cm spacing (published range 45 to 60 cm), planted 12 cm deep. Large tubers like dahlias need far more room than flower bulbs: just 2.25 tubers per square metre.
Why do small bulbs need so many more per area than large bulbs?
Bulb count per area grows with the square of the spacing. A 50 cm x 50 cm patch holds 49 muscari bulbs (7 x 7 at 6.5 cm spacing) but only 16 tulips at 12.5 cm spacing. That is why naturalising drifts of crocus and snowdrops are sold in bags of 50 or 100.
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