Tool
Bulb planting calculator
Use the size of the bulb to work out planting depth and spacing — and how many you need for a bed.
Your result
Plant about 15 cm deep, 13 cm apart
- Bulb size (cm)
- Bed length (m)
- Bed width (m)
That is roughly 49 bulbs per m², or about 49 bulbs for this bed.
What this calculator does
Bulbs are planted at a depth tied to their own size, and the usual rule of thumb is two to three times the bulb's height deep, spaced about two to three times its width apart. Enter the bulb's approximate size and the tool applies that rule, then works out how many sit in a given bed. It is a starting point: the packet or supplier often gives exact figures for a particular variety.
When to use it
- Working out how deep to plant bulbs of unknown size.
- Deciding how many bulbs to buy for a border or pot.
- Spacing a drift so it looks full without over-crowding.
How to use it
- Measure the bulb. A rough diameter is enough; bulbs vary, so round to the nearest centimetre.
- Measure the bed you want to fill, inside the edges.
- Read the result for depth, spacing and bulb count, then adjust to taste.
Worked example
A tulip bulb about 5 cm across, planted three times its own size, goes in roughly 15 cm deep and about 12–13 cm apart. That is nearly 64 bulbs per square metre — so a bed 1 m by 1 m takes around 56 bulbs once the edges are allowed for.
Typical planting depths
| Bulb | Usual depth |
|---|---|
| Tulip | 10–15 cm |
| Daffodil | 10–15 cm |
| Allium | 10–15 cm |
| Crocus | 5–8 cm |
| Lily | 15–20 cm |
| Garlic clove | 5 cm |
Depth suits the bulb's size, but soil matters too — plant a little deeper in light, sandy soil and shallower in heavy clay.
Limitations
- It is a rule of thumb. Some bulbs, such as lilies, prefer deeper planting than their size alone suggests.
- Square spacing only. Naturalised drifts are scattered, not gridded, and often look better for it.
- It ignores soil and drainage. Poor drainage is the main cause of bulb rot; add grit if in doubt.
Frequently asked questions
Which end of the bulb goes up?
The pointed end is the shoot and goes up, the flat, rooty end down. If unsure, plant on its side — the shoot finds its own way.
Can I plant bulbs closer than this?
For a bold one-season display in a pot, yes. In the ground, tight spacing crowds the bulbs and reduces flowering in later years.
Why is my clay soil a problem?
Bulbs rot in wet, heavy soil. Plant shallower, add grit beneath each bulb, or grow them in pots instead.
Related guides
Sources and research notes
Depth and spacing follow the common two-to-three-times rule from horticultural guidance; exact figures vary by bulb and soil.