Bulbs are planted on a grid, and the grid spacing is the whole design decision. Too wide and you get isolated flowers in a sea of mulch; too close and you get a competitive thicket where none of them reach full size. The usual figures are somewhere between three and five times the bulb’s own width, which for a standard daffodil or tulip means ten to twenty centimetres. Because the count goes with the square of the spacing, halving the gap quadruples the number of bulbs — which is why this is worth working out before ordering rather than after.
Bed, spacing and pack size
Spacing decides the count, and the count decides whether it looks like anything.
Result
The count goes with the square
This is the thing that surprises people. Spacing bulbs at twenty centimetres in a twelve square metre bed takes three hundred. At ten centimetres — half the gap — it does not take six hundred, it takes twelve hundred, because halving the spacing doubles the number in each direction and the two multiply. The area of bed each bulb gets falls by four.
The practical consequence is that the cheap-looking option is rarely the cheap one. Ten-centimetre spacing across a border that looks modest on paper is a four-figure bulb order, and the usual response — buying fewer and spacing them wider — produces a display that reads as a few scattered flowers rather than as a drift.
What the spacing is actually for
Bulbs are competing for light, water and nutrients in a fairly narrow window, and the spacing decides how hard they compete. Too close and the foliage shades the neighbours before the bulbs have finished building next year's flower, which shows up as a good first spring and a disappointing second one. Too far apart and each bulb does well individually but the display has no mass.
The rule of thumb is three to five times the bulb's own width, centre to centre. A large daffodil bulb is about five centimetres across, so fifteen to twenty-five centimetres. A crocus corm is about one, so five centimetres and very dense indeed. Small bulbs are cheap precisely because they are small, which is why a crocus lawn is affordable and a tulip one is not.
A grid is how you count them; it is not how you plant them. A block of bulbs in straight rows reads as a municipal planting.
Plant in odd numbers — seven, fifteen, twenty-three — in irregular drifts that are wider than they are deep, and let the spacing vary a little.
Depth, and what happens if you get it wrong
The usual depth is two to three times the bulb's own height, measured from the shoulder of the bulb rather than from the tip. A large daffodil goes down fifteen to twenty centimetres; a crocus goes down seven or eight. Too shallow and the bulb is lifted by frost, or splits into offsets and stops flowering; too deep and it uses its reserves getting to the surface and produces weak growth.
In heavy or wet soil, plant a little shallower and add grit under the bulb, because standing water around the base rots it faster than cold does. In light sandy soil, go a little deeper, because it drains freely and dries out.
| Bulb | Spacing | Depth | Per m² |
|---|---|---|---|
| Daffodil, large | 15 to 20 cm | 15 cm | 25 to 44 |
| Tulip | 10 to 15 cm | 12 cm | 44 to 100 |
| Crocus | 5 to 8 cm | 7 cm | 160 to 400 |
| Hyacinth | 15 cm | 12 cm | 44 |
| Allium | 20 to 30 cm | 15 cm | 11 to 25 |
| Snowdrop | 5 to 8 cm | 7 cm | 160 to 400 |
A worked example
- The gridA 6 x 2 m bed at 20 cm spacing takes 30 bulbs along and 10 across.
- The countThat is 300 bulbs, or 25 per square metre.
- PacksAt ten to a pack, 30 packs, or $240 at $8.
- CloserAt 15 cm the same bed would take 520 — 40 along and 13 across.
- Much closerAt 10 cm it would take 1,200. Four times the 20 cm order.
Three hundred bulbs for a twelve square metre bed is a normal, generous order for large bulbs. Twelve hundred is a specialist naturalising project, and it is worth knowing which one you are doing before the pack of ten has been multiplied by a hundred and twenty.
When to plant, and what happens next
Daffodils go in from late summer to early autumn, while the soil is still warm enough for root growth. Tulips go in later — late autumn — because planting them early in warm soil encourages the fungal problems that take a tulip bed apart. Both need a period of cold, which is why a bulb forced indoors has to be chilled first.
After flowering, let the foliage die back naturally. It looks untidy for six weeks and it is the period in which the bulb rebuilds itself for next year — cutting it off, or tying it into a bundle, is the usual reason a daffodil bed becomes a leaf-only bed after two or three seasons.
The same grid arithmetic applies to everything planted in rows or blocks: the plant spacing figure does it for annuals and perennials with their own spacing rules, and the seed quantity figure handles the same bed sown from seed rather than planted from bulbs. If the bed itself is being built or refilled, the raised bed soil figure sizes the volume.
Do
- Count on a grid, then plant in odd numbers in drifts.
- Plant at two to three times the bulb's own depth.
- Let the foliage die back completely before tidying.
- Add grit under bulbs in heavy or wet soil.
- Plant tulips late, once the soil has cooled.
Avoid
- Halving the spacing and quadrupling the order without meaning to.
- Planting in straight rows, which reads as municipal.
- Cutting the foliage off while the bulb is still rebuilding.
- Planting tulips early in warm soil.
- Assuming bulbs come back forever — most decline after three or four years.
Where the numbers stop being true
This counts a square grid over the whole bed. Real planting is not a grid: edges are irregular, there is usually something already growing in part of the bed, and the area that can actually be planted is smaller than the area of the bed. Reduce by whatever is already occupied.
Nothing here accounts for the fact that bulbs multiply. A naturalising planting spreads by offsets and by seed, so a bed planted at twenty centimetres may be a solid drift in five years without another bulb being bought — which is the argument for starting wider than you think.
And the count is of bulbs, not of flowers. A proportion of any bulk order will not emerge: some are damaged, some are dehydrated, and some are simply not viable. On a cheap bulk pack, allow five to ten percent for that rather than expecting every one to appear.
How the figures are produced
Bulbs along is the bed length divided by the spacing, rounded up, and bulbs across is the bed width divided by the same figure, rounded up. Their product is the total. Packs are the total divided by the bulbs per pack, rounded up, and the rate per square metre is the total divided by the bed area. The grid drawing shows the layout, capped at sixteen markers across.
Questions people ask
How many bulbs per square metre?
Twenty-five at 20 cm spacing, forty-four at 15 cm, and a hundred at 10 cm.
How close can I plant them?
About three times the bulb's own width. Closer than that and they compete, and the second year suffers.
How deep?
Two to three times the bulb's height, to the shoulder. Fifteen centimetres for a large daffodil.
Why did half of them not come up?
Usually dehydration or damage in a cheap bulk pack. Allow five to ten percent.
Do they come back every year?
Daffodils mostly do, and spread. Tulips usually decline after two or three years, and are often treated as annual.
Can I plant in grass?
Yes, and it looks best that way. Scatter them and plant where they fall, and do not mow until the foliage has died back.