Bulb Spacing Calculator
Find how many tulip, daffodil or allium bulbs a bed needs at a given spacing, in a square or staggered grid, and how deep to plant them.
🌱 What is Bulb Spacing?
Bulb spacing is the centre to centre distance between neighbouring flower bulbs when they are planted. It is the single decision that controls how many bulbs a bed swallows, how solid the display looks in its first spring, and whether the planting can keep going for a decade or exhausts itself in two seasons. Combined with the shape of the bed and the layout pattern you choose, spacing turns directly into a shopping list, because bulbs are bought by the hundred and the difference between 10 cm and 15 cm spacing more than doubles the order.
Gardeners meet this problem constantly. Someone planting a 3 m by 2 m front border with daffodils needs to know whether to buy 300 bulbs or 500. A landscaper quoting a municipal tulip bed has to convert a drawing in square metres into a purchase order and a labour estimate. A grower planting a cutting bed wants maximum stems per square metre without inviting botrytis. A gardener naturalising crocus in grass wants the opposite: wide, irregular spacing that will thicken up by itself over ten years. All four are asking the same geometric question with different answers.
Two things are widely misunderstood. The first is that layout pattern matters as much as spacing. A triangular or staggered grid, where every row drops into the notches of the row before it, packs roughly 15 percent more bulbs into the same bed than a square grid at the same centre to centre distance, because the rows sit only 0.866 times the spacing apart instead of the full spacing. It also reads as more natural, since no straight line of bulbs is visible from any viewing angle. The second is the fence-post effect: a 3 m row at 12 cm spacing holds 26 bulbs, not 25, because there is a bulb at both ends. In a small bed those edge bulbs can be a tenth of the total, which is the usual reason a quick area-divided-by-spacing-squared estimate comes up short.
Planting depth follows a separate rule that has nothing to do with spacing: plant a bulb about three times its own height deep, measured from the base of the bulb rather than the tip. A 5 cm tulip goes into a 15 cm hole, a small 2 cm crocus into a 6 cm hole. This calculator handles both questions at once. It counts bulbs exactly for the pattern you pick, reports the row structure so you can lay a line out in the bed, converts the count into a planting density you can compare against catalogue figures, and applies the depth rule to the bulb size you enter.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Daffodil Border, Staggered Rows
3 m by 2 m bed, 12 cm spacing, triangular layout, 4 cm bulbs
Example 2 — Tulip Strip in a Square Grid
4 m by 1.5 m strip, 15 cm spacing, square grid, 5 cm bulbs
Example 3 — Imperial Foundation Planting
10 ft by 4 ft bed, 6 in spacing, triangular layout, 1.5 in bulbs
Example 4 — Dense Crocus Carpet, Square Grid
8 ft by 3 ft edging, 4 in spacing, square grid, 1 in corms
❓ Frequently Asked Questions
🔗 Related Calculators
How many flower bulbs do I need per square metre?
At 10 cm spacing in a staggered layout you need roughly 115 bulbs per square metre, at 12 cm about 80, and at 15 cm about 51. A square grid at the same spacing gives about 13 percent fewer. Enter your bed size and spacing above for an exact count rather than a rounded density.
How far apart should tulip bulbs be planted?
Tulips are normally planted 10 to 15 cm apart, about 4 to 6 inches. Use 8 to 10 cm for a dense bedding display that will be lifted after flowering, and 12 to 15 cm where you want the bulbs to stay in the ground and build up clumps over several seasons.
How deep should I plant bulbs?
The standard rule is three times the height of the bulb. A 5 cm tulip bulb goes in a 15 cm hole, a 6 cm daffodil in an 18 cm hole and a small 2 cm crocus in a 6 cm hole. Measure the depth to the base of the bulb, not to its shoulder.
What is the difference between square and triangular bulb spacing?
In a square grid every bulb sits at the corner of a square of side s, so rows are s apart. In a triangular or staggered grid each row drops into the notches of the row before, so rows sit only 0.866 times s apart. That packs about 15 percent more bulbs into the same area.
Why is the row spacing multiplied by 0.866?
Three neighbouring bulbs in a staggered layout form an equilateral triangle of side s. The perpendicular height of that triangle is s times the square root of 3 divided by 2, which is 0.866 times s. That height is the distance between adjacent rows.
How many daffodil bulbs fit in a 3 by 2 metre bed?
At 12 cm staggered spacing a 3 m by 2 m bed takes 510 bulbs in 20 rows that alternate between 26 and 25 bulbs. That is 85 bulbs per square metre. Widening the spacing to 15 cm drops the requirement to about 310 bulbs.
Does the calculator count the bulbs on the edge of the bed?
Yes. It uses the fence-post count, so a 3 m row at 12 cm spacing holds 26 bulbs rather than 25: there is a bulb at both ends. That matters most in small beds, where the edge bulbs can be a tenth of the total.
Can I plant bulbs closer than the recommended spacing?
You can for a one-season display, and commercial bedding schemes often go as tight as 6 to 8 cm. The cost is that crowded bulbs compete for water and nutrients, produce smaller offsets and are much more prone to grey mould and basal rot in a wet spring.
How much extra should I order beyond the calculated number?
Add about 5 percent. Some bulbs arrive soft or mouldy and are not worth planting, a few get damaged during planting, and a small reserve lets you replace anything that rodents dig up in the first few weeks after planting.
Does bulb spacing change for layered or lasagne planting?
Yes. In a layered pot the large late bulbs go in the deepest layer at their normal spacing, and the smaller earlier bulbs sit in the gaps above them. Run the calculator once per layer using that layer's own bulb size and spacing, then add the layers together.
How deep do I plant bulbs in a container?
Slightly shallower than in open ground, typically two to two and a half times the bulb height, because a pot has limited depth and drains faster. Keep at least 2 cm of compost below the bulb base and 2 cm above the tip so the roots and shoots both have room.
Should spacing change between clay and sandy soil?
Spacing stays the same but depth changes. In heavy clay plant a little shallower than the three times rule, since cold wet soil at depth encourages rot. In free-draining sand plant a little deeper, which protects the bulb from frost heave and from drying out in summer.