Bulbs are little capsules of life, storing the energy flowers need to sprout healthy roots that dig deep into the chilled soil throughout the winter months. Planting bulbs in the fall ensures that these roots are strong and well-established, leading to brilliant shows of color in March, April and May. It also exposes them to the cold temperatures they need in order to thrive. The right time to plant bulbs depends on where you live, and special care may be required for certain varieties of flowers.
Plant Bulbs According to Your Hardiness Zone
The USDA Climate Hardiness Zone Map breaks the United States into 11 growing zones, based on average annual winter minimum temperatures. Use this map to determine your growing zone, and then refer to the following table for your fall bulb planting schedule.
Zone 1 (below -50 degrees F): Early September
Zone 2 (-50 to -40 degrees F): Early September
Zone 3 (-40 to -30 degrees F): September
Zone 4 (-30 to -20 degrees F): Late September to early October
Zone 5 (-20 to -10 degrees F): Late September to early October
Zone 6 (-10 to 0 degrees F): Mid-October
Zone 7 (0 to 10 degrees F): Early November
Zone 8 (10 to 20 degrees F): Early November
Zone 9* (20 to 30 degrees F): Early December
Zone 10* (30 to 40 degrees F): Mid-December
Zone 11* (Above 40 degrees F): Late December
*Additional chilling may be required to grow spring-flowering bulbs in these regions.
Additional Care Required for Colder and Warmer Zones
If your growing zone falls to either end of the spectrum, there are certain steps you should take to ensure that your bulbs will perform to their fullest potential. In the coldest areas, zones 1-4, bulbs should be planted in September so they have time to get established before the ground freezes. After planting, cover them in a 3-4 inch layer of mulch like hay, straw or shredded leaves to protect them from freezing injury during winter.
The warmest areas, zones 7-11, may not get cold enough for certain varieties of flowers. Large-flowered tulips, hyacinths and crocus will need supplemental chilling before planting. Place them in the refrigerator crisper drawer for 8 to 10 weeks, but keep them away from fruits and vegetables, which give off a gas that can inhibit bud growth. In these areas, where damaging temperatures are rare, bulbs can be planted well into December or early January.