Bulb Spacing Calculator

How to use this bulb spacing calculator

What this calculator does. This tool estimates the number of bulbs that can be placed in a rectangular garden bed while respecting a chosen border, spacing within each row, and spacing between rows. It supports a rectangular grid and a staggered triangular grid. The result is a geometric planting estimate, not a guarantee of survival, flowering, or mature plant health; soil, cultivar size, drainage, sunlight, and local climate still matter.

When to use it. Use it when planning a new bulb bed, checking how many bulbs to order, comparing a dense display with a looser naturalized layout, or preparing a row-by-row planting plan before work begins.

1. Choose Plant grid. Rectangular keeps positions aligned; triangular offsets every second row by half of the within-row spacing.
2. Select a bulb under Plant select, or choose Custom spacing. Then enter Length, Width, and Border in metres.
3. Enter Plant spacing (s) and Row spacing (r) in centimetres. Results update as you type.
4. Read Number of plants, Area, Usable area, Rows, and Average plants per row. Review the row table for staggered-row differences.
5. Use Download Excel to save the current assumptions and planting plan, or Reset to restore the documented defaults.

Input guide. Plant grid is required and accepts Rectangular or Triangular (staggered); triangular packing may fit more positions because alternate rows use half-spacing offsets. Plant select is required and supplies a practical example spacing for Allium, Crocus, Daffodil, Hyacinth, or Tulip; choose Custom when following a supplier's cultivar-specific directions. Length and Width are required decimal metre values greater than zero and must each exceed twice the Border. A realistic bed might be 5 m by 2 m. Border is a required nonnegative metre value, such as 0.10 m; increasing it reduces usable dimensions. Plant spacing (s) and Row spacing (r) are required positive decimal centimetre values, such as 10 cm. Smaller spacing raises the count, but crowding bulbs beyond the grower's recommendation can reduce air movement and future room. Enter decimals with a period, not a comma, and do not use scientific notation or unit letters in the fields.

Output guide. Number of plants is the exact whole count of valid geometric positions. Area is the full bed footprint in square metres. Usable area removes the border strip from all four sides. Rows is the number of row centerlines that fit across the usable width. Average plants per row divides the final count by the number of rows and can be fractional even though each row count is whole. The table's Offset from edge is measured from the bed's outer edge to each row centerline; Pattern identifies aligned or half-offset rows; Plants in row gives the row count; Cumulative plants is the running total.

Worked example. With a 5 m by 2 m bed, a 0.10 m border, 10 cm plant spacing, 10 cm row spacing, and a rectangular grid, the usable dimensions are 4.8 m by 1.8 m. The first bulb sits at the border and each additional bulb needs another 0.10 m. Therefore each row has floor(4.8 ÷ 0.10) + 1 = 49 bulbs, and the bed has floor(1.8 ÷ 0.10) + 1 = 19 rows. The displayed total is 49 × 19 = 931 plants.

Learn more. The Royal Horticultural Society's bulb planting guidance explains why planting depth, site conditions, and bulb type should complement any spacing calculation.