When to Plant Spring Flowering Bulbs

The first blooms of Snowdrops pushing through the cold ground in late winter are a welcome sight for any gardener – it signals the oncoming spring and a new gardening season. Snowdrops are shortly followed by Crocus, Iris, Tulips, Daffodils, and Winter Aconites, a breathtaking display of colors kissed by the spring sun. The warm days of summer and a garden in full bloom aren’t far off.

Planting spring bulbs: Depth, spacing, and soil quality are important

The term “flower bulbs” refers to true bulbs and other bulb-like structures such as rhizomes, stems, corms, tubers, and tuberous roots. Spring bulbs, also known as hardy bulbs, create some of the showiest and exciting flower blooms in the garden, from late winter to early summer, depending on the species. After blooming, they continue to grow and then store food in the bulb to ensure the plant’s survival through deep winters and periods of drought. After their growth is complete, the leaves die back and the plant becomes dormant until the following spring.

Most spring bulbs, with the exception of tulips and hyacinths, can be naturalized – that is, each bulb multiplies, creating additional bulbs and flowers each season. These can be separated after blooming for plantings elsewhere or left to grow freely to fill in large areas.

Soil Quality

When planting bulbs, soil quality is important. If you plant them in dense clay or otherwise wet and soggy soil, chances are they may fail. Make sure the soil drains well. If not, mix a few inches of compost in with the soil, or plant the flowers in raised garden beds. Add bone meal and a general fertilizer (avoid high nitrogen) at planting time to encourage robust blooms and growth. Fertilizer should be mixed into the top 8 inches of soil and not the hole the bulbs are planted in, as it may burn the roots.

Temperature matters

Which month in fall to plant spring-flowering bulbs depends on where you live. They must be planted in autumn to give them time to establish roots and experience roughly 10-12 weeks of chill before establishing top growth in spring. The optimum time to plant is when soil temperatures drop below 60 degrees F (this is usually when air temperatures are regularly 40-50 degrees), roughly 6-8 weeks before your typical first hard frost. If your corner of the world doesn’t get frost, you can still force spring blooms by storing spring bulbs in your refrigerator for 12-16 weeks and then planting them.

Depth and spacing

The rule of thumb when planting bulbs is to plant them 3-4 times as deep as the width of the bulb. Spacing depends on the variety, its mature size, and its ability to naturalize (see chart below). Water in the bulbs after planting, but they generally won’t need additional water during the fall unless it’s an unusually dry season. Cover with 2-3 inches of mulch after planting and spray a rodent repellant to discourage squirrels or other rodents from digging up your new bulbs (this apparently is a delicacy for them). If rodents are particularly nasty in your area, add a wire mesh such as hardware cloth or chicken wire on the soil surface and hold it in place with bricks until the ground freezes. Planting in masses will provide the best flower display rather than one here and there, which makes the flowers in bloom look rather lonely.

Average spring bulb planting dates by Zone

• Zones 4 and 5 September-October
• Zones 6 and 7 October-November
• Zones 8 and 9 – November-December
• Zone 10 – Late December-early January

Resources:

• What is my Hardiness Zone?
• To learn when your first frost date is, see our first and last frost guide here.
• To learn the ins and out and ups and downs of planting fall bulbs, see our flower bulb planting guide here.

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