Article — Bulb Spacing Calculator (Tulips, Daffodils, Crocus)
Bulb spacing calculator — bulbs per square foot and on-center spacing
Bulb spacing is the distance between bulb centers in a planting grid. For a target density of 5 tulips per square foot, on-center spacing is √(144 / 5) = 5.4 inches. A 50 square foot bed at that density needs 250 bulbs. Standard densities run 4–6 per square foot for tulips and daffodils, 9–12 per square foot for crocus and snowdrops, 2 per square foot for alliums and lilies.
Spacing affects everything from disease pressure to display impact. Too tight, and bulbs compete for water and nutrients, get fungal infections, and stop flowering after a year or two. Too sparse, and the display looks thin. The calculator above converts between density and on-center distance so you can buy the right number of bulbs and plant them at the right grid.
What is bulb spacing?
Bulb spacing is the center-to-center distance between neighboring bulbs when planted on a regular grid. It is measured in inches (US) or centimeters (Europe). For a target density of N bulbs per square foot, the on-center spacing in inches equals √(144 / N), because each bulb occupies (144 / N) square inches and the square root of that area gives one side.
The math assumes a square grid, which is what most planters use. A triangular (hexagonal) grid packs about 15 percent more bulbs at the same on-center spacing, but is harder to lay out in the garden. Most reference guides and bulb catalogs use square-grid density, and so does the calculator above.
The Keukenhof gardens in Lisse, Netherlands, plant about 7 million tulip, daffodil, hyacinth, and crocus bulbs every year across 79 acres. At an average density of 16 bulbs per square foot for show-garden displays, that works out to about 1.7 million bulbs per hectare. Crews plant the whole site by hand over six weeks each autumn.
The bulb spacing formula
Three formulas cover all the bulb-spacing math. Total bulbs equals area times density. On-center spacing equals the square root of (144 / density) when density is bulbs per square foot. Total cost equals bulbs times unit price.
Total bulbs = area (ft²) × density (b/ft²)Spacing (in) = √(144 / density)Spacing (cm) = √(929 / density per ft²)Cost = bulbs × unit pricePlanting time ≈ bulbs / 35 per hrWorked example: a 50 square foot bed at 5 tulips per square foot needs 250 bulbs. On-center spacing is √(144 / 5) = 5.4 inches. At $0.45 per bulb the bed costs about $112. Planting at 35 bulbs per hour takes 7 hours.
Bulb spacing by flower type
Each bulb species has a typical density range. Bigger bulbs need more room; smaller bulbs pack tighter. Standard published densities reflect mature bulb size at second-year planting depth and account for typical root spread.
- Crocus = 9–12 per square foot, on-center spacing 3.5–4 in.
- Snowdrop = 12–16 per square foot, on-center spacing 3–3.5 in.
- Grape hyacinth = 9–12 per square foot, on-center spacing 3.5–4 in.
- Tulip = 4–6 per square foot, on-center spacing 5–6 in.
- Daffodil = 3–5 per square foot, on-center spacing 6–7 in.
- Hyacinth = 3 per square foot, on-center spacing 7 in.
- Large allium = 1–2 per square foot, on-center spacing 8–12 in.
- Asiatic lily = 1–2 per square foot, on-center spacing 8–10 in.
Bulb spacing and density choices
Density is a trade-off. Show-garden density (8–10 tulips per square foot, on-center 4 inches) gives a solid carpet of color but requires lifting and replacing every year because the bulbs cannibalize each other's resources. Standard density (4–6 tulips per square foot) gives a good display and lets bulbs perennialize for 2–3 years before splitting.
Planting depth and bulb spacing
Spacing matters most when paired with the right depth. The standard rule is plant at 2.5 times the bulb's height. Tulips and daffodils go 6–8 inches deep; crocus and snowdrops 3–4 inches; alliums 6–10 inches depending on species size.
Depth and spacing both affect frost heave resistance. Deep planting buffers against freeze-thaw cycles that lift shallow bulbs out of the soil. Tight spacing creates a small thermal mass that holds temperature slightly steadier. Both effects matter most in USDA Zones 4–6.
Bulb spacing cost and time math
Bulk pricing favors larger plantings. Standard tulips run $0.40–$0.60 per bulb in 100-bulb retail packs, dropping to $0.30–$0.40 in 500-bulb wholesale lots, and $0.20–$0.30 from Dutch growers in 5,000+ bulb orders. Premium varieties (parrots, fringed, doubles) run $1–$2 per bulb at retail.
Buy bulbs in late August or early September for the best price and selection. Late October sales drop bulb prices 30–50 percent, but selection narrows and bulb quality declines as cold stores deteriorate. Plant within two weeks of arrival to prevent dehydration.
Bulb spacing for naturalized plantings
Naturalized plantings — woodland edges, meadow drifts, lawn dots — use roughly random placement at 60–80 percent of formal density. Toss a handful from waist height and plant where each bulb lands. The irregular layout looks more natural and avoids the formal-bed look that clashes with woodland or meadow surroundings.
Best species for naturalizing: daffodils (perennialize for decades), crocus (multiply by offsets), snowdrops (spread by seed and offset), Spanish bluebells, species tulips like T. tarda, and grape hyacinth. Avoid hybrid tulips and hyacinths for naturalizing — most modern varieties decline after 2–3 years and disappear by year 5.
Container plantings using layered bulb beds (tall species deep, short species shallow) ignore the standard spacing math. Total density can hit 25–40 bulbs per square foot across three layers, with tulips on the bottom at 6 in deep, daffodils at 4 in, and crocus at 2 in. The container provides limited space, so use one-year compositions and lift after bloom.
Common bulb spacing mistakes
Three errors recur. First, over-tight spacing in perennial beds — bulbs compete, decline, and stop flowering by year 3. Second, ignoring depth: a tulip planted at 3 inches instead of 7 frost-heaves and rots. Third, mixing bulb sizes without spacing for the biggest: a bed planted at 9 bulbs per square foot (crocus density) but including hyacinths becomes overcrowded as the hyacinths mature. Plan spacing for the largest species in the planting. A fourth mistake worth avoiding is planting too early in warm autumns — bulbs put down roots before the ground cools, then push leaves above the surface and lose them to frost. Wait until soil temperature drops below 60 °F at 4-inch depth, typically late September in Zone 5 and mid-November in Zone 8.