Spring Bulb Calculator

Spring bulbs are planted in fall and bloom months later, so the number you buy now decides how full your beds look next spring. This spring bulb calculator tells you how many tulips, daffodils, crocus, hyacinths, alliums or grape hyacinths fit a planting area at the right spacing, how many to buy with a small spare, and how deep to plant them. It works in square feet and inches, like the other tools on the site.

Bulbs are sold by the bag or by the dozen, and the spacing on the package is given in inches, which makes it hard to know how many to order for a bed measured in feet. The calculator does that conversion for you and rounds the purchase up so you are not short on planting day.

How to use the spring bulb calculator

1. Enter the planting area in square feet. Multiply length by width for a rectangular bed. For a round bed, multiply 3.14 by the radius squared.
2. Choose the bulb type. Each type has its own spacing and planting depth, so the count changes with your selection.
3. Read the results. You get the number of bulbs to plant, the number to buy including a 5% spare, the spacing between bulbs and the depth to plant.

The count assumes bulbs spaced evenly across the whole area, which gives a full, dense look. Many gardeners plant in clusters and leave gaps, in which case you will need fewer. The section on planting designs below explains how to scale the number up or down.

The spring bulb math

Bulbs are spaced on a grid, so the number that fit depends only on the area and the spacing. A square foot is 144 square inches, and each bulb takes up a square as wide as its spacing.

Bulbs to plant = area (sq ft) × 144 ÷ spacing (in) ÷ spacing (in)
Bulbs to buy = bulbs to plant × 1.05, rounded up

Worked example: a tulip bed

A bed of 20 square feet is planted with tulips at 5 inch spacing. The bed holds 20 × 144 ÷ 25 = 115 bulbs. With a 5% spare, you buy 115 × 1.05 = 120.75, which rounds up to 121 bulbs, so a typical bag of 100 plus a second smaller bag would cover it.

Worked example: daffodils along a border

A 50 square foot border takes daffodils at 6 inch spacing. The bed holds 50 × 144 ÷ 36 = 200 bulbs, and with the spare you buy 210.

Worked example: crocus in a patch

Crocus are small and planted close, at 3 inches apart. A 100 square foot area planted at full density holds 100 × 144 ÷ 9 = 1,600 bulbs, and the purchase with spare is 1,680. Because crocus are usually scattered in loose drifts and not planted in a solid mat, most gardeners buy a quarter to a half of that number, so a lighter planting uses far fewer.

Bulbs per square foot

If you plant at the spacings used by the calculator, you can estimate quickly:

• 3 inch spacing (crocus, grape hyacinths): 16 bulbs per square foot
• 5 inch spacing (tulips, hyacinths): about 6 bulbs per square foot (5.76)
• 6 inch spacing (daffodils, alliums): 4 bulbs per square foot

Spacing and depth for each bulb

The calculator uses these typical figures. Your package may give a slightly different range, and if it does, follow the package.

• Tulips: 5 inches apart, 6 to 8 inches deep
• Daffodils: 6 inches apart, about 6 inches deep
• Crocus: 3 inches apart, 3 to 4 inches deep
• Hyacinths: 5 inches apart, about 6 inches deep
• Alliums: 6 inches apart, about 6 inches deep, with the largest varieties spaced wider
• Grape hyacinths: 3 inches apart, about 3 inches deep

A common rule of thumb is to plant each bulb at a depth of about three times its height, measured from the base of the bulb, with the pointed end up. That gives small bulbs shallow holes and big bulbs deep ones, and it is a useful check if you are planting a bulb that is not on the list.

Choosing bulbs and thinking about bloom time

Bulbs bloom in a rough sequence through spring, and planting a few types together stretches the display. Crocus are among the first, often flowering in late winter or very early spring. Daffodils and hyacinths follow, tulips come next in mid spring, and alliums bloom in late spring into early summer. The exact dates depend on your climate and on the variety, but the order is dependable.

Pick firm, plump bulbs. Large bulbs, which are usually labeled with a size in centimeters, tend to produce bigger flowers, and soft, moldy or shriveled bulbs are best left in the store. Buy as early as you can for the best selection, and store the bulbs in a cool, dry, ventilated spot until planting, not in a sealed plastic bag.

When to plant spring bulbs

Plant in fall, once the soil has cooled and a few weeks before the ground freezes. Bulbs need a period of cold to bloom well, and they also need time to grow roots before winter. In much of the northern United States that means September through October, and in milder areas it can run into November or December. If you have missed the usual window, bulbs planted late, as long as the ground is not frozen, will often still bloom, though sometimes a little later or smaller.

Check your area’s first frost with the frost dates by ZIP code tool, and look up your zone with the growing zone finder. In warm climates, where winters do not give bulbs enough cold, tulips and hyacinths are often chilled in a refrigerator for about six to eight weeks before planting, kept away from ripening fruit, since the gas it releases can harm the flower inside the bulb.

How to plant spring bulbs

1. Pick a spot with good drainage. Bulbs rot in soil that stays wet. Most bulbs like full to part sun, and many bloom before trees leaf out, so spots under deciduous trees can work well.
2. Loosen the soil. Dig the bed to the planting depth and mix in a little compost. Our compost calculator shows how much your bed needs.
3. Dig a trench or individual holes. For a lot of bulbs, a single wide hole at the right depth is faster than digging each one.
4. Set the bulbs pointed end up. Roots grow from the flat base. If you cannot tell which end is up, plant the bulb on its side, and it will find its way.
5. Space them evenly. Use the spacing from the calculator, or arrange them in a loose cluster.
6. Cover and water. Backfill the soil, press it gently and water well to settle it and start root growth.
7. Mulch. After the soil has cooled, add a layer of shredded leaves or bark. The leaf mulch calculator shows how much you need.

Planting designs: clusters, drifts and layers

How you place bulbs matters as much as how many you plant. Straight rows look stiff, and most designers prefer clusters, with an odd number of bulbs in each group and a natural, scattered outline. A drift of 25 daffodils looks richer than the same bulbs spread one at a time across a bed.

A simple way to plan a cluster is to take the full-density number from the calculator and plant about half to three quarters of it, leaving gaps where perennials will fill in. For naturalizing, scatter bulbs by hand over the area and plant them where they land.

You can also layer bulbs in one deep hole, an approach sometimes called lasagna planting. The largest bulbs, such as tulips or daffodils, go at the bottom, a layer of soil goes over them, and smaller bulbs such as crocus go closer to the surface. The layers bloom in sequence, and one bed puts on a display for weeks.

Protecting bulbs from squirrels, voles and deer

Tulips and crocus are the favorite foods of squirrels, chipmunks and voles, and tulip flowers are a favorite of deer. Daffodils, alliums, hyacinths and grape hyacinths are generally less appealing to these animals, which makes them reliable choices where wildlife is a problem. If you want to plant tulips anyway, covering the bed with chicken wire or hardware cloth until the ground freezes, or planting the bulbs in wire cages, keeps most diggers out. Daffodil bulbs are poisonous if eaten, so keep them away from pets and small children.

Caring for bulbs after they bloom

After the flowers fade, leave the leaves in place. The leaves make the food that the bulb stores for next year’s flowers, and cutting them too early weakens the plant. Wait until the foliage has yellowed and withered, usually about six weeks after blooming, before removing it. Snipping off spent flower heads on tulips and daffodils helps the plant put energy into the bulb and not into seed. Tying or braiding daffodil leaves is not recommended, since it reduces the leaf area that collects sunlight.

Many bulbs, especially daffodils, return and multiply year after year. Tulips often fade after a few seasons, particularly hybrids, so many gardeners replant them every year or two for the best display. A low-nitrogen bulb fertilizer in fall or at the first sign of growth in spring helps bulbs that you want to keep.

Fitting bulbs into your garden plan

Bulbs are some of the easiest plants to place, because their foliage fades just as perennials grow in and cover it. Plant them among hostas, daylilies and other perennials that come up late, and the leaves hide the dying bulb foliage. The garden planner can help you map the spots, and the plant spacing calculator covers your vegetables and other plantings. The fall garden prep guide lists the other jobs that go along with bulb planting.

Common bulb planting mistakes

• Planting too shallow. Shallow bulbs are easy prey for squirrels and may flower poorly. Use the depth rule.
• Planting upside down. The pointed end goes up. Bulbs planted upside down may struggle to emerge.
• Soggy soil. Bulbs rot in wet ground. Choose a well-drained spot or raise the bed.
• Cutting the leaves too soon. Wait for them to turn yellow, or next year’s flowers will be smaller.
• Planting in rows. Clusters and drifts look more natural than straight lines.
• Buying too few. A small number of bulbs looks sparse. Use the calculator and round up.
• Planting too early in warm weather. Bulbs planted into warm soil can sprout leaves too soon. Wait for the soil to cool.

Frequently asked questions