Bulb Spacing Calculator
Calculate optimal flower bulb spacing, planting depth, and quantity for any bed size. Supports grid, staggered, circular, and naturalized patterns.
About
Incorrect bulb spacing produces one of two failures: overcrowding causes root competition and fungal disease; excessive gaps leave bare soil and waste planting stock. The difference between a professional-looking display and a patchy disappointment comes down to geometry. This calculator uses the recommended center-to-center distances published by the Royal Horticultural Society and major Dutch growers for 25+ common species. It computes total bulb count N for rectangular, circular, or custom beds using four layout algorithms: uniform grid, hexagonal stagger (which increases density by a factor of 2β3 over square packing), concentric rings, and naturalized drift.
Planting depth d follows the standard rule of 3Γ bulb height, adjusted per species. The tool accounts for edge margins so bulbs are not placed flush against bed borders. Limitation: spacing recommendations assume well-drained, loamy soil at temperate latitudes. Heavy clay or sandy conditions may require 10 - 20% wider spacing. Pro tip: purchase 5 - 10% extra bulbs to replace non-viable stock.
Formulas
For a rectangular bed with dimensions L (length) and W (width), and a center-to-center bulb spacing of s, the number of bulbs depends on the planting pattern.
Grid Pattern
Ngrid = floor(L β 2ms + 1) Γ floor(W β 2ms + 1)
Staggered (Hexagonal) Pattern
Row spacing: r = s Γ β32
Odd rows are offset by s2, yielding approximately 15% more bulbs than a grid in the same area.
Circular Bed
For a bed of radius R, concentric rings at radius rk = k Γ s:
nk = floor(2Ο Γ rks)
Ncircle = 1 + Kβk=1 nk
Planting Depth
d = 3 Γ hbulb
Where m = edge margin (typically s2), s = center-to-center spacing, hbulb = bulb height, and K = floor(R Γ· s).
Reference Data
| Bulb Species | Spacing cm | Spacing in | Depth cm | Depth in | Height cm | Bloom Season | Hardiness Zone |
|---|---|---|---|---|---|---|---|
| Tulip | 12 | 5 | 15 | 6 | 30 - 60 | Mid Spring | 3 - 8 |
| Daffodil (Narcissus) | 15 | 6 | 15 | 6 | 30 - 45 | Early - Mid Spring | 3 - 9 |
| Hyacinth | 12 | 5 | 12 | 5 | 20 - 30 | Mid Spring | 4 - 9 |
| Crocus | 8 | 3 | 8 | 3 | 8 - 15 | Late Winter - Early Spring | 3 - 8 |
| Allium (Large) | 20 | 8 | 15 | 6 | 60 - 120 | Late Spring - Early Summer | 4 - 10 |
| Allium (Small) | 10 | 4 | 10 | 4 | 15 - 30 | Late Spring | 4 - 9 |
| Iris (Dutch) | 10 | 4 | 12 | 5 | 45 - 60 | Late Spring | 5 - 9 |
| Snowdrop (Galanthus) | 8 | 3 | 8 | 3 | 10 - 15 | Late Winter | 3 - 7 |
| Grape Hyacinth (Muscari) | 8 | 3 | 8 | 3 | 15 - 20 | Mid Spring | 4 - 8 |
| Lily (Asiatic) | 30 | 12 | 15 | 6 | 60 - 120 | Early - Mid Summer | 3 - 8 |
| Lily (Oriental) | 30 | 12 | 18 | 7 | 90 - 150 | Mid - Late Summer | 4 - 9 |
| Gladiolus | 15 | 6 | 12 | 5 | 60 - 150 | Summer | 7 - 10 |
| Dahlia | 45 | 18 | 10 | 4 | 30 - 150 | Mid Summer - Frost | 8 - 11 |
| Ranunculus | 15 | 6 | 5 | 2 | 25 - 45 | Spring - Early Summer | 8 - 11 |
| Anemone | 10 | 4 | 5 | 2 | 15 - 30 | Spring | 5 - 9 |
| Freesia | 8 | 3 | 5 | 2 | 25 - 35 | Spring - Summer | 9 - 10 |
| Scilla (Bluebell) | 10 | 4 | 10 | 4 | 15 - 30 | Spring | 4 - 8 |
| Fritillaria (Crown Imperial) | 20 | 8 | 20 | 8 | 60 - 90 | Mid Spring | 5 - 8 |
| Fritillaria (Snakeβs Head) | 10 | 4 | 10 | 4 | 20 - 30 | Mid Spring | 3 - 8 |
| Cyclamen (Hardy) | 15 | 6 | 5 | 2 | 10 - 15 | Autumn - Winter | 5 - 9 |
| Camassia | 15 | 6 | 12 | 5 | 45 - 90 | Late Spring | 3 - 8 |
| Crocosmia | 10 | 4 | 8 | 3 | 60 - 90 | Mid - Late Summer | 5 - 9 |
| Eranthis (Winter Aconite) | 8 | 3 | 5 | 2 | 8 - 10 | Late Winter | 4 - 7 |
| Begonia (Tuberous) | 25 | 10 | 5 | 2 | 20 - 40 | Summer - Autumn | 9 - 11 |
| Canna Lily | 45 | 18 | 10 | 4 | 90 - 180 | Summer - Frost | 7 - 11 |