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Bulb Spacing Calculator

Ready to calculate
13 Bulb Presets.
Rectangular + Triangular.
Depth + Bloom Guidance.
100% Free.
No Data Stored.

How it Works

01Measure the Bed

Enter length, width, and an optional border (path edge or fence buffer) in m, cm, in, or ft.

02Pick the Bulb

Choose from 13 popular bulbs (tulips, daffodils, alliums, crocus...) — spacing presets auto-fill, or use Custom.

03Choose Grid

Rectangular for tidy borders, triangular (offset) for ~15% denser drifts and a more naturalistic look.

04Get Bulb Count + Depth

Exact bulbs needed, m² area, density, planting depth, bloom window, and optional total cost.

What is a Bulb Spacing Calculator?

Spring bulbs — tulips, daffodils, allium, crocus, hyacinths — are some of the highest-impact plants in the gardener's toolkit: a single autumn afternoon of planting buys six to eight weeks of guaranteed spring colour, year after year, with almost zero ongoing maintenance. The catch is that bulbs only look spectacular when planted at the right density. Plant them too sparsely and you get a sad scattering of single stems; pack them too tightly and they compete for soil nutrients, produce smaller blooms, and rot from poor airflow. Our Bulb Spacing Calculator solves the count-and-grid problem in one pass: pick the bulb species, enter your bed dimensions, choose rectangular (formal borders) or triangular / offset (naturalistic drifts, ~15% denser), and instantly get the exact number of bulbs to order, along with planting depth, bloom window, and optional total cost. The 13 built-in bulb presets — Allium, Anemones, Bluebells, Crocus, Cyclamen, Daffodil, Dwarf Daffodil, Fritillaria, Hyacinths, Iris Reticulata, Muscari, Snowdrops, and Tulips — use spacing values from the Royal Horticultural Society (RHS) bulb planting guide, Cornell Cooperative Extension, and the Netherlands Flower Bulb Information Center. Spacing for large bulbs (daffodils, fritillaria, allium) ranges from 15-20 cm centre-to-centre; small bulbs (crocus, snowdrops, muscari, iris reticulata) sit at 7-10 cm. Row spacing is conventionally 1.25-1.5× the plant spacing, which the calculator pre-fills automatically and lets you override. A Custom plant option lets you enter any spacing for species not in the preset list (lily, dahlia tubers, gladiolus corms, etc.). Designed for home gardeners planning a spring border, landscape designers ordering wholesale bulbs for a client install, and naturalising drifts in lawns or under deciduous trees, the calculator runs entirely in your browser — no account, no data stored. Pro tip: the triangular grid produces about 15% more bulbs at the same minimum centre-to-centre distance and is much closer to how bulbs grow in the wild — gardeners almost universally prefer it for daffodil, crocus, and allium drifts. Use rectangular for formal display beds, parterres, and cut-flower production rows where uniformity matters.

Pro Tip: Pair this with our Plant Spacing Calculator for perennials and shrubs, our Mulch Calculator for the autumn top-dressing over freshly-planted bulbs, or our Soil Calculator if you need to amend the bed first.

How to Use the Bulb Spacing Calculator?

Choose Plant Grid: Rectangular for formal borders, parterres, and cut-flower rows — bulbs sit on a uniform cols × rows grid. Triangular (offset) for naturalistic drifts, lawn-naturalising, and woodland edge planting — alternating rows are offset by half a spacing, packing about 15% more bulbs into the same area at the same minimum distance.
Enter Bed Length and Width: Use any unit (cm, m, in, ft) — the calculator converts internally. Most gardeners use metres for borders (e.g. 3 × 2 m) and feet for raised beds (e.g. 8 × 4 ft).
Set Border (optional): If you want to leave a path-edge buffer or fence inset (so the outermost bulbs don't flop onto the lawn or hardscape), enter the border width. The calculator subtracts 2× the border from each dimension to get the usable planting area.
Pick the Bulb Species: 13 popular bulbs — Allium, Anemones, Bluebells, Crocus, Cyclamen, Daffodil, Dwarf Daffodil, Fritillaria, Hyacinths, Iris Reticulata, Muscari, Snowdrops, Tulips — auto-fill spacing and row-spacing presets. Or pick "Custom plant" and enter your own values for lily, dahlia, gladiolus, etc.
Override Spacing if Needed: Defaults follow RHS / Cornell guidance, but you may want closer spacing for cut-flower production (denser = more stems per bed) or wider for jumbo-grade bulbs. Spacing unit is independent — typically cm, but inches work fine.
Add Price per Bulb (optional): Wholesale tulip bulbs are typically $0.30-$0.80 each; specialty narcissus and fritillaria run $1-$5. The calculator multiplies your unit price by the bulb count to give a total order cost — useful when budgeting against a quote from a wholesale supplier.
Read Bulb Count, Density, Depth, and Bloom Window: The result card shows total bulbs, the grid pattern (cols × rows for rectangular, n offset rows for triangular), usable area in m², density per m², standard planting depth (typically 2-3× bulb height), and the typical bloom window (early spring → autumn).

How is bulb spacing calculated?

Bulb counting reduces to packing problems on a 2D rectangle. The calculator implements both standard packing patterns used in horticulture: rectangular (square / cartesian grid) and triangular (offset / hexagonal close-pack).

Spacing presets follow the Royal Horticultural Society (RHS) bulb planting guidelines, Cornell Cooperative Extension, and the Netherlands Flower Bulb Information Center. Planting depth follows the standard 2-3× bulb height rule, with small adjustments for soil type and hardiness zone.

Rectangular Grid

Bulbs sit on a uniform grid with constant spacing s along rows and constant row-spacing r between rows. With usable bed dimensions L_u × W_u (after subtracting 2× the border):

cols = ⌊L_u / s⌋ + 1

rows = ⌊W_u / r⌋ + 1

Bulb count = cols × rows

Triangular (Offset) Grid

Alternating rows are shifted by s/2 — every bulb sits at the centre of an equilateral triangle formed by its three nearest neighbours. The vertical row-height drops to s·√3/2 ≈ 0.866·s:

row_height = s × √3 / 2

rows = ⌊W_u / row_height⌋ + 1

Per-row count: ⌊L_u / s⌋ + 1 (even rows) or ⌊(L_u − s/2) / s⌋ + 1 (odd / offset rows)

Density at the same minimum bulb-to-bulb distance: 2 / (√3 · s²) bulbs / m², which is about 15.5% higher than the rectangular density of 1 / (s · r) when r = s. This is the same as the densest possible packing of equal circles in a plane — the hexagonal close-pack used in everything from atom crystals to honeycomb cells.

Standard Bulb Spacing (RHS / Cornell / Netherlands Flower Bulb Center)

Spacing is measured centre-to-centre. Most bulbs use a row-spacing of 1.25-1.5× the plant spacing.

  • Tulips: 12-15 cm spacing, 15 cm depth (2-3× bulb height). Bloom mid-late spring.
  • Daffodils: 15-20 cm spacing, 15 cm depth. Bloom mid-spring. Naturalise vigorously over many years.
  • Dwarf Daffodils (e.g. Tete-a-tete): 8-12 cm spacing, 10 cm depth.
  • Allium (giant ornamental onion): 8-15 cm spacing for smaller cultivars, 20-30 cm for giants like A. giganteum. 15 cm depth. Bloom late spring / early summer.
  • Hyacinths: 10-15 cm spacing, 12.5 cm depth. Bloom mid spring.
  • Crocus: 5-10 cm spacing, 7.5 cm depth. Bloom early spring. Excellent for naturalising in lawns.
  • Snowdrops (Galanthus): 5-10 cm spacing, 7.5 cm depth. Bloom late winter — the earliest spring bulb.
  • Muscari (grape hyacinth): 5-10 cm spacing, 7.5 cm depth. Bloom mid spring.
  • Iris Reticulata: 5-10 cm spacing, 7.5 cm depth. Bloom early spring.
  • Anemones (e.g. A. blanda, A. coronaria): 5-10 cm spacing, 5 cm depth. Soak corms 8-12 hours before planting.
  • Cyclamen (hardy cyclamen): 10 cm spacing, 5 cm depth. Bloom autumn / winter — exception to the spring-bulb pattern.
  • Bluebells (Hyacinthoides): 10 cm spacing, 10 cm depth. Bloom mid spring. Native to UK woodlands; plant in shade.
  • Fritillaria (crown imperial / snake's head): 20-30 cm spacing for crown imperial, 10 cm for F. meleagris. 15-20 cm depth.

Planting Depth Rule

The standard horticultural rule: plant the bulb at a depth 2-3× the bulb's vertical height, measured from the bottom of the planting hole to the soil surface. So a 5 cm tall tulip bulb goes 10-15 cm deep. Adjust:

  • Heavy clay soil: plant slightly shallower (avoid waterlogging) and add grit beneath the bulb.
  • Light sandy soil: plant slightly deeper (better moisture retention).
  • USDA zone 3-4 (very cold): plant 2-3 cm deeper for winter protection.
  • Zone 8-10 (mild): plant at standard depth, but most spring bulbs need pre-chilling 12-14 weeks at 5-9°C in the fridge before planting.

Naturalising vs Formal Display

  • Formal display beds: use rectangular grid with tight spacing (lower end of the recommended range). Replant or top up annually for tulips (which lose vigour after 1-2 years in most gardens). Daffodils and crocus can stay in place 5-10+ years.
  • Naturalising drifts: use triangular grid with the recommended spacing OR scatter handfuls and plant where they fall (toss-and-plant method). Best species for naturalising: daffodils, crocus, snowdrops, muscari, bluebells, anemones, allium. Worst: tulips (most modern hybrids decline rapidly).
  • Lawn naturalising: 50-100 bulbs per m² of lawn for a dense crocus / snowdrop carpet. Plant under tree canopies (deciduous) so bulbs get full sun in early spring before leaves emerge.
  • Cut-flower production rows: rectangular grid, tight spacing, single-cultivar rows for sequential harvest. Tulips for cutting: 8-10 cm spacing.
Real-World Example

Bulb Spacing Calculator – Worked Examples

Example 1 — Formal Tulip Border (Rectangular). 3 m × 2 m bed, 0.2 m border, 12 cm tulip spacing, 15 cm row spacing.
  • Usable area = (3 − 0.4) × (2 − 0.4) = 2.6 × 1.6 = 4.16 m².
  • cols = ⌊2.6 / 0.12⌋ + 1 = 21 + 1 = 22 columns.
  • rows = ⌊1.6 / 0.15⌋ + 1 = 10 + 1 = 11 rows.
  • Total bulbs = 22 × 11 = 242 tulip bulbs.
  • At $0.50 per bulb (typical wholesale single-colour) = $121.00 total.
  • Plant 15 cm deep in early-to-mid autumn (4-6 weeks before first hard frost).

Example 2 — Naturalised Daffodil Drift (Triangular). 5 m × 4 m woodland-edge area, no border, 18 cm daffodil spacing.

  • Usable area = 5 × 4 = 20 m².
  • row_height = 18 × √3 / 2 = 15.59 cm = 0.156 m.
  • rows = ⌊4 / 0.156⌋ + 1 = 25 + 1 = 26 rows (alternating offset).
  • Even-row bulb count: ⌊5 / 0.18⌋ + 1 = 27 + 1 = 28 per row × 13 rows = 364.
  • Odd-row bulb count: ⌊(5 − 0.09) / 0.18⌋ + 1 = 27 + 1 = 28 per row × 13 rows = 364.
  • Total bulbs ≈ 728 daffodil bulbs.
  • Compare to rectangular at the same 18 cm spacing: ⌊5/0.18⌋+1 = 28 cols × ⌊4/0.18⌋+1 = 23 rows = 644 bulbs. Triangular gives 13% more bulbs in the same space at the same minimum distance — the classic naturalising advantage.

Example 3 — Crocus Lawn-Naturalising Carpet. 10 m × 10 m of lawn, 8 cm crocus spacing, triangular grid.

  • Usable area = 100 m².
  • Density (triangular at 8 cm): 2 / (√3 × 0.08²) ≈ 180 bulbs / m².
  • Total ≈ ~18,000 crocus bulbs for a continuous carpet.
  • Practical alternative for naturalising on a budget: scatter 50-100 bulbs per m² randomly (toss-and-plant), giving ~5,000-10,000 bulbs total for the same area with a more naturalistic appearance.
  • Wholesale crocus bulbs: $0.10-$0.20 each in 1000+ quantities. Budget: $500-$2000 for a 100 m² carpet.

Example 4 — Mixed Border with Allium Accents. 4 m × 1 m border, 0.1 m border inset, 25 cm Allium giganteum spacing, rectangular grid.

  • Usable area = 3.8 × 0.8 = 3.04 m².
  • cols = ⌊3.8 / 0.25⌋ + 1 = 15 + 1 = 16 columns.
  • rows = ⌊0.8 / 0.25⌋ + 1 = 3 + 1 = 4 rows.
  • Total = 64 Allium giganteum bulbs at 15 cm depth.
  • At $4.00 per giant allium bulb = $256.00 total. Premium accent — use sparingly mixed with smaller, cheaper bulbs.

Example 5 — Cut-Flower Tulip Production Row. 20 m × 1.2 m grow-row, 8 cm spacing (tight, for cut flowers), 12 cm row spacing, rectangular.

  • Usable area = 24 m² (no border for production).
  • cols = ⌊20 / 0.08⌋ + 1 = 250 + 1 = 251 cols.
  • rows = ⌊1.2 / 0.12⌋ + 1 = 10 + 1 = 11 rows.
  • Total = 251 × 11 = 2,761 tulip bulbs per 20 m row.
  • Yield: 1 stem per bulb (single-flowered cultivars), so 2,761 saleable cut stems per row per spring.
  • At wholesale cost $0.40 per bulb and retail $1.50 per cut stem: $1,104 input → $4,142 output gross per 20 m row per season.

Who Should Use the Bulb Spacing Calculator?

1
Home Gardeners — Spring Border Planning: Plan a tulip / daffodil border, calculate exact bulb order quantity, avoid the common mistake of under-ordering (bare patches) or over-ordering (cramped, rotting bulbs).
2
Naturalising Drifts (Lawns + Woodland Edge): Calculate bulbs needed for crocus, snowdrop, daffodil, or muscari drifts. Use triangular grid for the natural look; budget 50-100 bulbs/m² for dense lawn naturalising.
3
Landscape Designers + Garden Contractors: Cost-out client bulb orders accurately (count × per-bulb price); compare rectangular formal vs triangular naturalistic install density side-by-side.
4
Cut-Flower Growers: Plan tight-spaced production rows for tulips, daffodils, and allium for the spring cut-flower market. Rectangular grid with reduced spacing maximises stems per square metre.
5
Public Park + Civic Planters: Calculate large-scale bulb plantings for parks, roundabouts, civic display beds. The triangular grid gives ~15% more bulbs per dollar at the same visual density.
6
Container Gardeners: Use the calculator with small bed dimensions (e.g. 0.5 × 0.3 m for a window box) to plan layered "bulb lasagne" plantings — tulips deep, daffodils middle, crocus top.
7
School + Community Gardens: Budget bulb orders for classroom planting projects. Crocus and snowdrops are fastest to flower (4-12 weeks after planting in spring) — best for impatient students.

Technical Reference

Bulb Anatomy and Planting Orientation. A true bulb (allium, daffodil, hyacinth, tulip, lily) consists of a basal plate (modified compressed stem) at the bottom from which roots emerge, surrounded by fleshy storage scales (modified leaves), all enclosed in a papery tunic (in tunicate bulbs like tulip and onion) or naked (in scaly bulbs like lily). Plant pointed end up, basal plate down. If unsure of orientation (rare for tulip / daffodil, common for some lily corms and anemone tubers), plant on their side — the shoot will find its way up and the roots will find their way down.

Hexagonal Close-Pack and Why Triangular Wins. The densest possible packing of equal circles in a 2D plane is the hexagonal close-pack, where each circle touches six neighbours. The triangular (offset) bulb grid is exactly this packing: alternating rows are shifted by half a spacing, so each bulb has six nearest neighbours at the minimum distance, and the row-height is s·√3/2 ≈ 0.866·s instead of the rectangular spacing s. Density: 2 / (√3 · s²) bulbs/m² for triangular vs 1 / s² for square (when r = s) — a ~15.5% increase. This is the same packing principle that governs honeycomb cells, soap-bubble walls, and the densest atom packing in metal crystals (FCC and HCP structures).

Spacing Sources.

  • Royal Horticultural Society (RHS) Bulb Planting Guide — the UK gardening standard reference.
  • Cornell Cooperative Extension Bulb Garden Guide — comprehensive US extension service guidance.
  • Netherlands Flower Bulb Information Center (iBulb.org) — the global authority on Dutch-bred bulbs (which is most of the commercial bulb market).
  • Royal General Bulb Growers Association (KAVB) — the cultivar-classification authority for tulip, daffodil, hyacinth, etc.

Planting Depth — The 2-3× Bulb Height Rule. Measured from the bottom of the planting hole (where the bulb sits) to the final soil surface. Standard depths:

  • Tulips, daffodils, hyacinths: 15 cm (6 in).
  • Allium giganteum: 20 cm (8 in).
  • Smaller allium, dwarf daffodil, hyacinths: 12.5 cm (5 in).
  • Crocus, snowdrops, muscari, iris reticulata: 7.5 cm (3 in).
  • Anemones, cyclamen: 5 cm (2 in).
  • Fritillaria imperialis (crown imperial): 20 cm (8 in), on its side to prevent water collecting in the hollow crown and rotting the bulb.

Best Planting Time by Region.

  • USDA zones 3-7 (most of US, UK, northern Europe): Plant September-November, 4-6 weeks before first hard frost. Bulbs need 12-16 weeks of soil temperatures below 9°C (48°F) for proper root development and bloom triggering.
  • USDA zones 8-10 (mild winter regions, e.g. California, Florida, southern Spain): Pre-chill bulbs in the fridge crisper drawer (NOT with apples or other ethylene-producing fruit) at 5-9°C for 12-14 weeks, then plant in late December-January. Tulips and hyacinths almost always need pre-chilling here; daffodils and crocus often don't.
  • Mediterranean climates: Iris, ranunculus, anemones, freesias do well planted in autumn for late winter / early spring bloom.

Bulb Grades and Sizes. Bulbs are sold by circumference (cm) — the larger the bulb, the more flowers and bigger blooms, but the higher the cost.

  • Tulips: 11/12 cm (standard), 12/+ cm (top-size), 14/+ cm (jumbo / display grade).
  • Daffodils: "Round" = 1 nose, "Double-Nose I (DN1)" = 2-3 noses (most popular for landscape), "Mother bulbs" = 3+ noses (for show / specimen plantings).
  • Hyacinths: 14/15 cm (standard bedding), 16/17 cm (top size), 18/19 cm (forcing / display).
  • Allium giganteum: 18/20 cm (standard), 22/24 cm (top size).

Pest and Disease Considerations.

  • Squirrels and voles eat tulip and crocus bulbs. Daffodils, allium, fritillaria, snowdrops, hyacinths are toxic / unpalatable and rarely touched. Protection: chicken-wire mesh over the bed or 1-2 cm of grit underneath.
  • Tulip fire (Botrytis tulipae): a fungal disease that destroys tulip bulbs. Crop-rotate — don't plant tulips in the same bed two years running.
  • Narcissus bulb fly: larvae burrow into daffodil bulbs. Remove yellowing foliage promptly after bloom and discard rather than composting.
  • Slugs eat emerging shoots in spring. Wool pellets, copper tape, beer traps, or organic slug pellets (iron phosphate-based) protect emerging foliage.

Naturalising Lifespan by Species.

  • Excellent (10+ years, multiplies vigorously): daffodils, crocus, snowdrops, muscari, allium, scilla, chionodoxa.
  • Good (5-10 years): hyacinths, dwarf iris, fritillaria meleagris, anemones.
  • Mediocre (2-5 years): most tulip species (Darwin Hybrid tulips are the most perennial).
  • Poor (1-2 years, treat as annuals): most modern tulip hybrids (Triumph, Single Late, Parrot — replant annually for best display); hyacinths in mild climates without proper chilling.

Top-Dressing After Planting. Apply a 2-5 cm layer of mulch (composted bark, leaf mould, or well-rotted manure) over the freshly planted bed in late autumn. This insulates against frost heave, retains moisture, suppresses weeds, and slowly feeds the bulbs. Don't use fresh manure (burns roots) and don't mulch too deeply (5+ cm can prevent shoots from emerging in spring).

Key Takeaways

Bulb planting density determines whether a spring display is spectacular or sad. The Bulb Spacing Calculator solves the count problem in one pass: pick from 13 popular bulbs (allium, anemones, bluebells, crocus, cyclamen, daffodil, dwarf daffodil, fritillaria, hyacinths, iris reticulata, muscari, snowdrops, tulips) or use Custom; choose rectangular for formal beds or triangular (offset) for naturalistic drifts (~15% denser at the same minimum bulb-to-bulb distance — equivalent to the hexagonal close-pack of equal circles); enter bed dimensions and an optional border inset. The result: exact bulb count, usable area in m², density per m², standard planting depth (2-3× bulb height), bloom window, and optional total cost. Spacing presets follow RHS, Cornell Cooperative Extension, and Netherlands Flower Bulb Information Center guidelines. Plant 4-6 weeks before the first hard frost in autumn; tulips in mid-autumn, daffodils and most other bulbs slightly earlier. For naturalising drifts, plant 25-50% more bulbs than the formal-grid count — bulbs look much better when they overlap and intermingle.

Frequently Asked Questions

What is the Bulb Spacing Calculator?
It is a planting-design tool for spring bulbs (tulips, daffodils, allium, crocus, hyacinths and 8 more) that solves the count-and-grid problem in one pass. Pick the bulb species, enter your bed dimensions and an optional border, choose rectangular (formal borders) or triangular / offset (naturalistic drifts, ~15% denser), and instantly get the exact number of bulbs to order along with planting depth, bloom window, density per m², usable area, and optional total cost. Spacing presets follow Royal Horticultural Society (RHS), Cornell Cooperative Extension, and Netherlands Flower Bulb Information Center guidelines. Custom-plant mode lets you enter any spacing for species not in the preset list.

Pro Tip: Pair this with our Plant Spacing Calculator for perennials and shrubs.

How far apart should I plant tulip bulbs?
Standard tulip spacing is 12-15 cm (5-6 in) centre-to-centre for a formal display border, with rows 15 cm apart. For cut-flower production rows (where you want maximum stems per m²), tighten to 8-10 cm. For naturalised drifts (rare for tulips, since most modern hybrids decline rapidly after the first year), 15-20 cm with the triangular grid. Plant 15 cm (6 in) deep measured from the bottom of the planting hole, and 4-6 weeks before the first hard frost. In mild climates (USDA zone 8-10), pre-chill in the fridge for 12-14 weeks before planting in late December.
How far apart should I plant daffodil bulbs?
Standard daffodil (Narcissus) spacing is 15-20 cm (6-8 in) centre-to-centre with rows about 20 cm apart. Plant 15 cm deep. Dwarf daffodils (Tete-a-tete, Minnow, Hawera) sit at 8-12 cm spacing and 10 cm depth. Daffodils are excellent naturalisers — they multiply vigorously and last 10+ years in the same spot — so for naturalised drifts, the triangular grid gives the most natural-looking density. Spacing too tight crowds the bulbs and reduces flower size after a few years; spacing too wide leaves gaps even after multiplication.
Rectangular or triangular grid — which is better?
Triangular (offset) grids pack about 15% more bulbs into the same area at the same minimum bulb-to-bulb distance (the hexagonal close-pack — same principle as honeycomb cells). It also looks much more natural — no obvious rows from any viewing angle — making it the gardener's favourite for drifts of daffodils, crocus, allium, snowdrops, and muscari. Rectangular grids are best for formal display beds, parterres, and cut-flower production rows, where uniform rows and predictable spacing matter (easier to weed, harvest, or replace gaps). Both produce the same blooms — the choice is aesthetic and operational.
How deep should I plant bulbs?
The standard horticultural rule: plant the bulb at a depth 2-3× the bulb's vertical height, measured from the bottom of the planting hole to the final soil surface. So a 5 cm tall tulip bulb goes 10-15 cm deep. Standard depths for common bulbs: tulips, daffodils, hyacinths, allium 15 cm; dwarf daffodils, dwarf hyacinths 10-12.5 cm; crocus, snowdrops, muscari, iris reticulata 7.5 cm; anemones and cyclamen 5 cm. Plant slightly deeper (2-3 cm extra) in USDA zones 3-4 for winter protection; slightly shallower in heavy clay soil to avoid waterlogging.
When should I plant spring bulbs?
USDA zones 3-7 (most of US, UK, northern Europe): Plant September-November, 4-6 weeks before the first hard frost. Daffodils and most other bulbs go in slightly earlier (September-October); tulips can go in last (October-November). Bulbs need 12-16 weeks of soil temperatures below 9°C (48°F) for proper root development and bloom triggering. USDA zones 8-10 (mild winters): Pre-chill bulbs in the fridge crisper drawer at 5-9°C for 12-14 weeks (NOT with apples — they release ethylene gas that kills bulb embryos), then plant in December-January. Crocus and daffodils sometimes flower without pre-chilling here; tulips almost never do.
How many bulbs do I need per square metre?
Depends on species and grid: large bulbs (daffodil, allium, fritillaria) at 15-20 cm spacing: 25-45 bulbs/m² rectangular, 30-50 bulbs/m² triangular. Medium bulbs (tulip, hyacinth) at 12-15 cm spacing: 45-70 bulbs/m² rectangular, 50-80 bulbs/m² triangular. Small bulbs (crocus, snowdrops, muscari, iris reticulata) at 7-10 cm spacing: 100-200 bulbs/m² rectangular, 115-230 bulbs/m² triangular. For dense lawn-naturalising carpets of crocus or snowdrops, gardeners often plant 200-500 bulbs/m². For sparse naturalising drifts, 25-50 bulbs/m² scattered handful-style produces a more natural look.
Can I use this for lily, dahlia, or gladiolus?
Yes — pick Custom plant from the species dropdown and enter your own spacing. Standard guidance: Lily bulbs: 20-30 cm spacing, 15-20 cm depth. Dahlia tubers (NOT a true bulb — a tuberous root): 60 cm spacing, 10-15 cm depth, plant after last frost in spring (not autumn). Gladiolus corms: 10-15 cm spacing, 10 cm depth, plant succession-style every 2 weeks from late spring for continuous summer bloom. Iris (rhizomes, NOT bulbs): 30-40 cm spacing, just below soil surface. Begonia tubers: 30 cm spacing, 2.5 cm deep.
Why does my bulb count seem high?
Bulbs look spectacular only when planted at high density. A 3 × 2 m tulip border at standard 12 cm spacing genuinely needs 240+ bulbs for a proper display — many gardeners under-order based on intuition and end up with sparse, disappointing beds. Two practical adjustments: (1) for budget reasons, use larger spacing within the recommended range and the triangular grid (gets you to ~85% of the visual impact at ~75% of the bulb cost); (2) for naturalised drifts, scatter handfuls and plant where they fall instead of using a strict grid — visually equivalent to ~50-70% of the calculated count.
What about bulb lasagna (layered planting)?
"Bulb lasagna" is a high-impact technique where you plant 3-4 bulb species at different depths in the same container or bed for sequential bloom. Bottom layer (15-20 cm deep): daffodils or large tulips. Middle layer (10-12 cm): hyacinths, dwarf daffodils, smaller tulips. Top layer (5-7 cm): crocus, muscari, snowdrops, iris reticulata. Each layer sits on top of the layer below — bulbs find their way up around obstructions. Use this calculator three times — once per layer at the appropriate spacing — and combine the bulb counts. A 0.5 × 0.3 m container (15 m² × small fraction) can easily hold 30-60 bulbs across 3 layers for an 8-10 week sequential display.
How much do bulbs cost?
Wholesale prices (per bulb, in 100+ quantities): Tulips $0.30-$0.80 (specialty / new cultivars up to $2). Daffodils $0.40-$1.20 (Double-Nose II $0.60-$1.50). Hyacinths $0.60-$1.20. Crocus $0.10-$0.20. Snowdrops $0.30-$0.60 (in-the-green far better than dry bulbs). Allium giganteum $3-$5 (premium accent). Muscari, scilla, chionodoxa $0.10-$0.25. Fritillaria imperialis $5-$12 (very premium). Retail at garden centres adds 30-60% markup — order from specialist bulb suppliers (Brent and Becky's, Colorblends, Old House Gardens, Sarah Raven, Peter Nyssen) for the best pricing on volume orders.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our ToolsACE horticulture team combines published bulb-planting guidance from the Royal Horticultural Society (RHS), Cornell Cooperative Extension, and the Netherlands Flower Bulb Information Center with a fast browser-based grid solver. The calculator covers 13 of the most popular spring and naturalising bulbs — tulips, daffodils, dwarf daffodils, allium, crocus, hyacinths, muscari, snowdrops, bluebells, anemones, cyclamen, fritillaria, and iris reticulata — plus a custom-plant mode for anything else. Two grid modes are supported: rectangular (cols × rows, ideal for tidy borders) and triangular (offset rows packed at row-height s·√3/2, about 15% denser at the same minimum bulb-to-bulb distance — the gardener's favourite for naturalistic drifts). Border insets, mixed bed/spacing units (cm, in, m, ft), planting depth, bloom-window, and optional cost-per-bulb are all handled in one pass.

RHS Bulb Planting GuideCornell Cooperative ExtensionNetherlands Flower Bulb Information Center

Disclaimer

Estimates based on standard bulb-spacing guidance from RHS, Cornell Cooperative Extension, and the Netherlands Flower Bulb Information Center. Actual bulb requirements vary with cultivar size (jumbo vs standard vs miniature grades), soil type, USDA hardiness zone, and naturalising vs formal-display intent. For mass-naturalising drifts, gardeners often plant 25-50% more bulbs than the formal-grid count. For wet, heavy clay soils, increase planting depth slightly and add grit; in zones 3-4, plant deeper for winter protection. This tool does not replace site-specific horticultural advice.