Bulb Spacing Calculator

Every autumn the same question returns with the bulb catalogue: the bed is this big, the spacing on the packet says that — how many bulbs do I actually order? The answer is pure geometry, and this calculator does it properly: enter the bed’s area, the spacing between bulbs, and the planting pattern, and it returns the count for a square grid and for the tighter triangular (offset) pattern that professional plantings use — plus the area a given number of bulbs will cover, so a bargain pack can be audited before it is bought.

The Geometry Under the Bed

Two patterns organise nearly every planting. In a square grid, each bulb owns a square of side s (the spacing), so the density is simply 1/s² — at 6-inch spacing, s = 0.5 ft and each square foot holds 4 bulbs. In a triangular pattern, alternate rows are offset by half a spacing and the rows sit closer (s·√3/2 apart), packing each bulb into a rhombus of area s²·√3/2: the density becomes 2/(√3·s²), which is 2/√3 ≈ 1.155 times the grid's — 15.5% more bulbs in the same bed, 15.5% more flower in spring. That ratio is the whole horticultural argument for offset planting, and it is a theorem, not a tip: circles (and bulbs are planted as if circles) pack most efficiently on a triangular lattice, a result from Kepler's world that the bulb fields of Holland execute at hectare scale. The calculator prices both patterns for every bed so the choice — budget versus density of display — is made with the numbers on the table.

Worked Example: A Hundred Square Feet of Tulips

The defaults: a 100 sq ft bed, 6-inch spacing. Square grid: density 1/0.25 = 4 per sq ft → 400 bulbs. Triangular: 2/(1.732 × 0.25) = 4.62 per sq ft → 462 bulbs (the calculator rounds up, because beds do not accept fractional bulbs and a half-empty corner advertises itself all spring). Now vary the spacing and watch the square law bite: at 4-inch spacing the grid count is 9 per sq ft, 900 bulbs; at 8 inches it falls to 2.25 per sq ft, 225 bulbs. Halving the spacing quadruples the order — the single most useful intuition in bulb buying, and the reason catalogue photography (shot at spacings no amateur budget survives) should be read as aspiration, not instruction. Packet guidance by genus sits in this arithmetic's light: large tulips and daffodils are commonly spaced 4–6 inches, hyacinths 5–6, small bulbs like crocus and snowdrops 2–3 — each spacing a density decision wearing a recommendation's clothes.

Depth, Drifts and the Honest Extras

Three field realities adjust the clean geometry. Depth is not spacing: the rule of thumb plants a bulb at three times its own height (a 2-inch tulip bulb goes 6 inches deep), which governs the trowel work, not the count — but deep-planted large bulbs and shallow small ones can be layered in the same square foot (the lasagne method), in which case the calculator is run once per layer and the totals added: the bed's area serves two crops at different depths and different seasons of bloom. Design eats geometry: drifts and clusters plant denser in the middle and thinner at the edges for a naturalised look, so a drift planting's true count is the calculator's figure read as a budget to distribute rather than a lattice to obey. Attrition is real: squirrels, rot, the occasional dud and the gardener's own mis-trowelling tax every planting — the 10% overage in the widget's note is the profession's shrug, priced in. Buy the overage; the spring display will not point out which bulbs were spares, and the spares themselves, planted in a nursery corner, become next year's free stock once they have fattened through a season of undisturbed growth.

Formal Beds, Meadows and Pots: Reading the Count in Context

The same density appears in three costumes. Formal bedding (municipal displays, parterres) plants at or beyond the triangular density and lifts the bulbs after flowering — maximum count, maximum cost, maximum spectacle, the calculator's triangular mode with the overage kept. Naturalising (grass, orchards, woodland edges) inverts the economics: bulbs are scattered at a fraction of bedding density — often the equivalent of 8–12-inch spacings — and left for years to multiply, so the count is a founding population, not a display: run the calculator at a wide spacing and expect time to close the gaps. Containers compress everything: pot displays plant at half the bed spacing or tighter for a single-season show, and the "area" is the pot's mouth — a 12-inch pot is 0.79 sq ft, which at 3-inch triangular spacing takes 2/(1.732 × 0.0625) × 0.79 ≈ 15 bulbs, the layering trick usually doubling it. One formula, three budgets — the page's work is to make the number explicit before the catalogue makes it for you.

A Thousand Daffodils: The Naturalising Sum

The catalogue's favourite round number deserves its own audit. One thousand daffodil bulbs, naturalised at 8-inch triangular spacing: the density is 2/(1.732 × 0.444) ≈ 2.60 per sq ft, so the thousand cover about 385 sq ft — a drift roughly 20 × 19 feet, or a generous orchard corner. Priced against the alternative fantasy — bedding all thousand at tulip tightness (6-inch triangular, 4.62 per sq ft) — the same bulbs would cover only 216 sq ft. Naturalising buys area with patience: the founding thousand multiply by offsets over the years, filling their 385 sq ft toward the density the bedding budget buys outright. The calculator's role in the romance is modest and essential: it prices both strategies in the same units before the order is placed, while the choice between spectacle now and meadow eventually is still yours.

Corms, Tubers and the Wide-Spacing Clause

The geometry is democratic — it prices anything planted at points. Gladiolus corms at 5-inch triangular spacing run 2/(1.732 × 0.174) ≈ 6.6 per sq ft for the cutting garden's regimental rows. Dahlia tubers invert the scale: each plant is a clump demanding 18–24 inches, so at 2-ft grid spacing the density is one plant per 4 sq ft and a 100 sq ft bed holds 25 dahlias — a count small enough that the calculator's rounding-up, applied bulb by bulb, becomes the whole budget conversation. The lesson generalises across the bulb catalogue's extended family: whatever the propagule — bulb, corm, tuber, rhizome — the order quantity is area divided by the territory each plant will occupy at flowering, and the territory, not the packet, is the document to consult.

Related Tools

More from the Biology Calculators hub: the Vegetable Seed Calculator for the spring counterpart of this autumn arithmetic, and the Water Soluble Fertilizer Calculator for feeding what the spacing plants.

Frequently Asked Questions

Why does the triangular pattern fit more bulbs?

Because offset rows nestle into the gaps of the row in front, the way oranges stack in a crate. Each bulb's territory shrinks from a square (s²) to a rhombus (s²·√3/2 ≈ 0.866·s²) at the same nearest-neighbour distance, so the same spacing yields 15.5% more plants per area — the densest possible arrangement of equal circles, which is why commercial growers default to it.

Should I plant at the packet spacing?

Packet spacing is a sound default for a full-but-not-wasteful display in open ground. Go tighter (a size down on this calculator) for containers and one-season bedding where fullness now outranks longevity; go wider for naturalising, where each bulb is expected to become a clump. What the packet spacing protects against is the failure mode at each extreme: starved, spindly crowding versus a bed that reads as a rumour of flowers.

How deep should the bulbs go?

The standard rule is a planting hole three times the bulb's own height, measured to the bulb's base: tulips and daffodils typically 6–8 inches deep in consequence, small bulbs 3–4. Depth buys frost protection, rodent discouragement and (for tulips in warm climates) the cool rest they need — it does not change the count this page computes, except in layered plantings where depth is what lets two layers share the area.

How many bulbs come in a typical pack, and how far do they go?

Retail packs run from 10 to 50; the audit is this calculator read backwards — density times pack size is coverage. Fifty tulips at 6-inch triangular spacing cover about 10.8 sq ft: a patch roughly 3 × 3.5 feet. First-time buyers consistently overestimate pack coverage by a factor of three or more, which is the entire commercial reason this page exists.

My bed is round / L-shaped. How do I get its area?

Round: π × radius² (a 6-ft-diameter circle is about 28.3 sq ft). L-shaped: split it into two rectangles and add. Irregular: use the average width times the length as an honest estimate and lean on the overage — bulb geometry forgives area estimates far more readily than it forgives running out in the final corner.

Can I use this for onion sets, garlic or seedlings?

Yes — the mathematics is planting density, indifferent to what is being planted. Garlic at 6-inch spacings in rows, onion sets at 4 inches, bedding plants at their label spacing: enter the spacing honestly and the count follows. The vegetable-specific version, with germination rates and row layouts, is the sister calculator linked above.