Planting bulbs requires thinking ahead: spring-flowering bulbs need to be planted in fall in order to bloom come show time. The bulbs need a certain amount of time to get established before winter's freezing weather sets in, and they need enough time exposed to cool soil temperatures to be properly chilled. But fall doesn't occur at the same time on the calendar in San Antonio, Texas, as it does in Minneapolis, Minnesota. So how do you know when to plant? Follow the steps below and you'll have plenty of flowers come springtime.
The simplest way to know when to plant bulbs is to use the USDA Climate Hardiness Zone Map as your planting guide. This map breaks the country into 11 growing zones based on average annual winter minimum temperatures. First use the map to find which hardiness zone you live in. Then, consult the list below to know when to plant spring-flowering bulbs in your zone.
Zone 1 (below -50° F): Early September
Zone 2 (-50 to -40° F): Early September
Zone 3 (-40 to -30° F): Mid-September
Zone 4 (-30 to -20° F): Late September to early October
Zone 5 (-20 to -10° F): Late September to early October
Zone 6 (-10 to 0° F): Mid-October
Zone 7 (0 to 10° F): Early November
Zone 8 (10 to 20° F): Early November
Zone 9* (20 to 30° F): Early December
Zone 10* (30 to 40° F): Mid-December
Zone 11* (Above 40° F): Late December
* Additional chilling may be needed to grow spring-flowering bulbs in these regions.
In coldest areas (zones 1 through 4), bulbs grow and perform best if planted early enough to get established before the ground freezes. Mulch the bed a month after planting with a 3- to 4-inch layer of hay, straw or shredded leaves. This will allow the soil to stay warm enough for the bulb roots to get established and will protect tender bulbs from freezing injury during winter, especially if the snow cover is sparse.
In the warmest-winter areas (zones 7 through 11), select bulb varieties that are best adapted to warm winters, such as wild tulips native to southern Europe. Most large-flowered tulips, hyacinths and crocus will need additional chilling before planting to successfully flower in the spring. To chill the bulbs before planting, place them in the refrigerator crisper for 8 to 10 weeks (but keep bulbs away from fruits or vegetables, which they give off ethylene gas and can cause the bud inside the bulb to abort), then plant. Since the ground rarely freezes deeply, if at all, in these areas, bulbs can be planted into December or even early January.