Bulb Spacing Calculator
Enter your garden bed dimensions and preferred spacing to find out exactly how many bulbs you need. Choose from 15 popular bulb types with recommended spacings pre-filled, or enter a custom spacing. Switch between a rectangular grid and a staggered triangular layout, set a border clearance to keep edges clean, and toggle between imperial (inches/feet) and metric (centimetres/metres). The show-your-work panel traces every step of the calculation.
How to calculate how many bulbs you need
The number of bulbs that fit in a garden bed depends on three things: the usable planting area after subtracting any edge clearance, the plant-to-plant spacing, and whether you are planting in aligned rows or a staggered triangular pattern.
For a rectangular grid, the formula is straightforward:
- Usable length = bed length - 2 x edge clearance
- Usable width = bed width - 2 x edge clearance
- Columns = floor(usable width / spacing) + 1
- Rows = floor(usable length / spacing) + 1
- Total bulbs = rows x columns
For a triangular (staggered) grid, every other row is shifted by half a spacing, and the distance between rows is spacing x sin(60 degrees) - about 86.6% of the spacing. This allows roughly 15% more bulbs in the same area and produces a softer, more natural look.
How to use this calculator
Select your unit system (imperial feet and inches, or metric metres and centimetres), then enter your bed length and width. Pick a bulb type from the dropdown - this automatically pre-fills the recommended spacing and planting depth. If you want a different spacing, enter it in the override field. Set an edge clearance if you want to keep a border free of bulbs, then choose rectangular or triangular planting. All results update instantly.
The density output tells you how many bulbs per square foot or square metre you are planting. Fewer than 1 per sq ft is sparse; 4-9 per sq ft gives a full display; above 9 is very dense and may require dividing bulbs every few years to prevent overcrowding.
Always add 10-15% to your final order to account for bulbs that are damaged or fail to sprout - bulb suppliers expect this and many sell by the dozen or half-dozen for this reason.
Spacing recommendations by bulb category
Different bulb families need different spacings to thrive. Large bulbs like tulips, daffodils, and hyacinths need 6 inches (15 cm) between them to avoid competing for water and nutrients. Smaller bulbs such as crocus, grape hyacinth, snowdrops, and iris reticulata can be planted as close as 3 inches (7.5 cm) apart.
Very large ornamental alliums (Allium giganteum and similar varieties) need 8 inches (20 cm) or more. Lilies, which grow from large scaly bulbs rather than tunicate bulbs, need 12 inches (30 cm) because their root systems are extensive and they can persist for many years.
The reference table above lists the full set of recommended spacings. As a general rule, plant bulbs at a depth equal to two to three times the bulb diameter.
Rectangular vs triangular planting patterns
A rectangular grid lines every bulb up in straight columns and rows. It is easy to mark out with string lines and familiar to most gardeners, but it can look regimented, especially once the foliage fills in.
A triangular or hexagonal pattern offsets every other row by half a spacing. The rows are also closer together (approximately 86.6% of the plant-to-plant spacing), which means a 10 x 4 ft bed that holds 80 tulips in a rectangular layout can hold around 92 in a triangular one - a 15% gain. More importantly, the result looks like a naturalistic drift of flowers rather than a parade-ground formation.
For formal knot gardens and cut-flower beds, rectangular spacing is fine. For borders, parkland naturalization, or cottage-garden displays, use triangular spacing.
Planting depth and aftercare tips
The depth rule - plant at two to three times the bulb diameter - exists because it insulates the bulb against frost and anchors the flower stem. Plant too shallow and bulbs frost-heave in cold climates; plant too deep and flower stalks struggle to push through, and the bulb exhausts its energy before blooming.
After flowering, leave foliage in place for at least 6 weeks. The leaves manufacture the starch that recharges the bulb for next year. If you cut them back too soon, the bulb will bloom poorly or not at all in subsequent seasons. Braiding or banding the leaves keeps the border tidy without cutting them off.
Bulbs in heavy clay soil benefit from sharp sand mixed into the planting hole. In very wet sites, raise beds or plant on a slight slope. Most bulbs prefer well-drained soil - they rot in waterlogged ground.
Common bulb spacing and planting depth guide
| Bulb type | Spacing (in) | Depth (in) | Approx. height (in) | Bulbs per sq ft |
|---|---|---|---|---|
| Tulip (large) | 6 | 6 | 24 | 4 |
| Tulip (small/species) | 4 | 5 | 10 | 9 |
| Daffodil | 6 | 6 | 16 | 4 |
| Hyacinth | 6 | 6 | 10 | 4 |
| Crocus | 4 | 3 | 5 | 9 |
| Allium (large) | 8 | 8 | 36 | 2 |
| Allium (small) | 4 | 4 | 18 | 9 |
| Grape Hyacinth | 3 | 3 | 6 | 16 |
| Snowdrop | 3 | 3 | 4 | 16 |
| Iris Reticulata | 3 | 3 | 6 | 16 |
| Fritillaria | 6 | 6 | 30 | 4 |
| Lily | 12 | 8 | 48 | 1 |
| Anemone | 4 | 3 | 8 | 9 |
| Cyclamen | 6 | 2 | 6 | 4 |
| Bluebell | 4 | 4 | 12 | 9 |
Recommended spacings are for standard flower displays. Plant depths follow the general rule of 2-3 times the bulb diameter.
Frequently asked questions
How many tulip bulbs do I need for a 4 x 10 foot bed?
A 4 x 10 ft bed (40 sq ft) with large tulips at 6-inch spacing and a 3-inch border clearance fits about 84 bulbs in a rectangular grid or roughly 97 bulbs in a triangular pattern. This calculator works it out for any size bed - just enter your dimensions and choose "Tulip (large)" from the bulb type dropdown.
What is the rule of thumb for bulb planting depth?
Plant bulbs at a depth equal to two to three times the bulb diameter. In practice: tulips and daffodils go 6 inches deep, hyacinths 6 inches, crocus 3 inches, grape hyacinth 3 inches, and lilies 8 inches. The calculator shows the recommended depth for each bulb type automatically.
What is the difference between rectangular and triangular planting?
In a rectangular grid every bulb aligns in straight columns and rows. In a triangular (staggered) grid every other row is shifted by half a spacing, and row spacing is about 86.6% of the plant spacing. The triangular layout packs roughly 15% more bulbs into the same bed and looks more natural, while the rectangular grid is easier to lay out with string lines.
How far apart should I plant bulbs in general?
Spacing depends on bulb size. Large bulbs like tulips, daffodils, and hyacinths need 6 inches between them. Medium bulbs like allium and anemone need 4-6 inches. Small bulbs like crocus, snowdrops, and grape hyacinth can be planted 3-4 inches apart. Very large bulbs like lilies need 12 inches. Check the reference table on this page for bulb-by-bulb guidance.
How many bulbs should I order to allow for wastage?
Add 10-15% to your calculated total when ordering. Some bulbs will be soft, damaged, or fail to sprout, and bulb suppliers typically round quantities to the nearest 10 or 25 anyway. For formal displays where every gap matters, ordering 15-20% extra gives you spare bulbs to fill any failures.
What is an edge clearance and why does it matter?
An edge clearance (also called a border) is the gap you leave between the outermost row of bulbs and the physical edge of the bed. A 3-inch clearance keeps bulbs from sitting right against brickwork or lawn edges where roots compete and drainage is poorest. It also gives the planting a neater appearance when the bed edge is visible.
Can I plant different bulb types at the same spacing?
Yes. Many gardeners plant small bulbs like crocus between large-bulb rows so the crocus fills the gaps in early spring before the tulips emerge. In that case use the spacing recommended for each type and consider them as separate layers. This calculator handles one bulb type per calculation - run it twice for mixed plantings.