Zones for Planting Tulips

Tulip Facts

• Tulips grow from specialized roots called tunicate bulbs that are broad on one end and pointed at the top where the plant emerges. Like other spring bulbs, they contain an embryonic plant, that includes the flower and nutrients to support it until the following spring. The tunicate bulb takes its name from the layer of tissue, or tunic, it adds each summer. The cues for the embryo within the bulb to start growing begin with temperature -- a period of chilling, placement in soil where the temperature is below 60 degrees Fahrenheit and the increasing light of the spring sun.

USDA Zones 3 through 5

• Tulip bulbs sit 6 to 8 inches below the soil's surface, so bulbs easily attain their chilling requirement of 12 to 16 in the colder areas that include USDA zones 3 through 5. This poses few problems where the days get shorter and the first hard freeze comes in October or early November. Plan in these areas in October after the soil temperature falls below 60 F during the day, but you can still plant through the end of November if the ground does not freeze.

USDA Zones 6 through 8

• Planting in USDA zones 6 through 8 happens later in October through the first weeks of December, but spring comes sooner, too. If you live in USDA zone 8b, you may choose to refrigerate the bulbs after you buy them to guarantee the bulbs will receive a full three- to four-month chilling period. After their chilling period, plant them in December. Depending on local conditions, tulips in USDA zone 8 may not successfully perennialize, or come back in succeeding years.

USDA Zones 9 through 11

• Tulips in USDA zones 9 to 11 should be treated as annuals -- if they are to bloom in succeeding years, you must refrigerate them and plant them in December through early January and dig them up after their foliage fades in early summer. In these areas, summer is typically too hot -- and sometimes too dry -- for tulips to survive, so during the heat of summer, return them to the refrigerator. Refrigerated bulbs should never rest near apples or other fruits that off-gas ethylene, a chemical that hastens the ripening process.

Forcing Tulips

• Florists perform something called forced blooming or bulb forcing to get tulips to bloom at a specific time. Around 22 weeks before sale, the bulbs are kept at 40 to 45 F, then planted in pots, watered and placed in bright light in a greenhouse. The plants bloom in six to eight weeks later, the same time as if they were planted in the ground. By controlling the temperature and light, the florist can manipulate bloom time.