Bulb Planting Calculator

The two rules that govern almost every bulb

Despite the huge variety of spring and summer bulbs available, planting them successfully comes down to two consistent rules: depth relative to bulb size, and spacing relative to bulb width. Depth affects winter insulation and how the emerging shoot finds its way to the surface; spacing affects both bloom size (crowded bulbs compete for nutrients and produce smaller flowers) and how full the display looks in its first year versus after a few seasons of natural multiplication.

Depth: two to three times bulb height

The classic planting depth rule is to measure from the base of the bulb (not the tip) to the soil surface, and aim for two to three times the bulb's own height. Larger bulbs like daffodils and alliums generally go toward the deeper end of that range, both because their vigorous root systems benefit from more soil volume and because greater depth offers more insulation against temperature swings for a bulb that will spend a long winter underground before flowering.

Spacing for bloom size vs. display density

Bulbs planted too close together compete for water and nutrients, often producing smaller flowers and weaker foliage over successive years even if the first bloom looks fine. Wider spacing gives each bulb more resources and generally larger, healthier blooms, but a newly planted bed at wide spacing can look sparse in its first year before bulbs naturalize and multiply to fill gaps. Many gardeners split the difference by planting in loose natural-looking clusters — odd numbers of 5, 7, or 9 bulbs grouped together with normal spacing within the cluster — rather than either a tight solid block or a sparse even grid.

Fall bulbs vs. summer bulbs

• Fall-planted (spring-blooming): tulips, daffodils, crocus, hyacinth, allium — plant 6-8 weeks before the ground freezes.
• Spring-planted (summer-blooming): dahlias, gladiolus, canna, caladium — plant after the last frost once soil has warmed.
• Spring bulbs are generally hardy and can overwinter in the ground in most climates.
• Many summer bulbs (especially dahlias and gladiolus) are tender and need lifting and indoor storage over winter in colder zones.

After-bloom care that affects next year's display

Once flowers fade, resist the urge to cut back bulb foliage immediately — the leaves continue photosynthesizing and storing energy in the bulb for next year's bloom for several weeks after flowering ends, and cutting them too early noticeably weakens future flowering. Deadheading spent flowers (removing just the bloom, not the foliage) redirects energy from seed production back into the bulb itself, which can meaningfully improve next season's display, especially for larger bulbs like daffodils and alliums.