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With the exception of a few types of bulbs that produce flowers in the fall, the majority of bulbs can be divided into spring blooming and summer blooming. Spring blooming bulbs include crocuses, tulips, daffodils, anemones, snowdrops, irises, hyacinths and fritillaria. These are hardy bulbs that are planted in the fall and require the cold weather of the winter months in order to sprout. Under the right conditions these flowers are perennials, and will reappear for a number of years. Some, such as daffodils, will naturalize, increasing in number over the years.
Spring flowering bulbs should be planted six weeks before the average date the ground freezes in order to allow roots to develop. Ideally, the bulbs should be planted before the first frost. A map has been developed that breaks the United States into sixteen bulb planting regions. This map is available in the internet, as well as in some gardening catalogs, magazines and reference books.
Region A is New England. Per the map, the optimum planting time for spring blooming bulbs is between September 15 and November 15.
Region B is the Mid-Atlantic Coastal region. Spring blooming bulbs should be planted between October 1 and November 30 in this region.
Region C is the Appalachian region. The planting period for bulbs runs from September 15 to November 30 in this zone.
Region D is the South Atlantic Coastal zone. The optimum planting time for this region is between October 15 and December 15.
Region E is the Great Lakes region. Spring blooming bulbs should be planted between September 15 and November 15 in this area.
Region F is the East Central region. Bulbs should be planted between October 1 and November 30.
Region G is the South Central zone. Planting of bulbs should take place between October 15 and December 15.
Region H is the Tropical zone, encompassing South Florida and Hawaii. Planting should occur between December 1 and January 31. However, because of the hot temperatures of this region, few spring blooming bulbs can be successfully grown.
Region I is the Gulf Coast region. The planting period for bulbs runs from October 1 through December 31. Spring blooming bulbs must be carefully selected to grow in this relatively mild region.
Region J is the Northern Central region. September 15 through November 1 is the optimum planting time for spring blooming bulbs.
Region K is the Central and Great Plains region. The planting period runs between September 30 and November 30.
Region L is the Rocky Mountains region. Bulbs should be planted between September 15 and November 1.
Region M is the Arid West. Bulbs should be planted in this region between September 30 and November 30.
Region N is the Northern Pacific Coast. Planting should occur between October 1 and December 1 in this area.
Region O is the Southern Pacific Coast. This region has two major fall planting seasons. Bulbs that are native to the Mediterranean and similar climates, such as freesias, should be planted from mid-August into December. Dutch bulbs should be planted from mid-October through late January.
Region P encompasses Alaska. The optimum planting time for spring blooming bulbs is between September 15 and October 15.
Well known varieties of summer blooming bulbs include lilies, dahlias, caladium and gladioli. Most summer blooming bulbs are tender bulbs, meaning they do not perennialize in areas that receive frost in the winter. In such areas they may be left in the ground to decompose and be replaced annually, or the bulbs may be removed from the ground and stored until it is time to replant.
Determining when to plant bulbs for summer blooms is less complicated than planting spring blooming bulbs. Summer blooming bulbs should be planted in spring, after the last frost. In areas with cold winters and late frosts, summer blooming bulbs can be started indoors during early spring, and planted outdoors after the last frost is past.
As a general guideline, in Canada and the northern United States summer blooming bulbs may be planted between April and June. In the central United States, bulbs should be planted between March and May. Planting should take place between February and April in the Southern United States.
For guidance on which bulbs should be planted, the gardener should first consult the Plant Hardiness Zones established by the United States Department of Agriculture. The map of the Plant Hardiness Zones is readily available on the internet or in gardening catalogs, books and magazines. This handy chart divides the United States into eleven hardiness zones. Zone 1 has average annual minimum temperatures of below -50 degrees Fahrenheit. The warmest zone, Zone 11, has average annual minimum temperatures above 40 degrees Fahrenheit. The gardener should confirm the bulbs that are to be planted are appropriate for the hardiness zone in which the gardener lives. Packages of bulbs generally contain a label that identifies the hardiness zones in which the bulbs will grow.
Bulbs are generally brought into garden centers just before the appropriate planting time for that zone. Bulbs should be planted promptly after purchase. Local garden centers can provide advice as to what bulbs are suitable for that zone, and when and how they should be planted. With a little planning, bulbs can bring the gardener pleasure for years on end.
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