AMES, Iowa—Bulb forcing can bring the bright colors and fragrances of spring indoors during winter. Tulips can be forced indoors from December through March, if steps are taken in the fall to prepare the bulbs. Iowa State University Extension and Outreach horticulturists share tips on having tulips blooming indoors during winter.
What is needed to successfully force tulips indoors?
High quality bulbs, a well-drained potting mix and containers with drainage holes in the bottom are needed to successfully force tulips indoors. To enjoy tulips in winter, gardeners must begin the forcing process in late summer or early fall.
Which tulips can be forced indoors?
The best tulip types for forcing include the Triumph, Single Early, Double Early and Darwin Hybrids. For the best selection of bulbs, visit local garden centers in September as soon as the bulbs arrive. Select large, firm bulbs. Avoid small, soft or blemished bulbs.
How do you force tulip bulbs indoors?
Begin by partially filling the container with potting soil. Then place the tulip bulbs on the soil surface. Adjust the soil level until the tops of the bulbs are slightly below the rim of the container. The number of bulbs to plant per pot depends on the size of the container. Generally, four to five bulbs are placed in a 5-inch-diameter pot, six to seven bulbs in a 6-inch-diameter pot. When placing tulip bulbs in the container, position the bulb so the flat side of the bulb faces the wall of the pot. When positioned in this way, the large lower leaf of each bulb will grow outward over the edge of the container forming an attractive border around the edge of the pot. Once properly positioned, place additional potting soil around the bulbs. However, do not completely cover the bulbs. Allow the bulb tops (noses) to stick above the potting soil. For ease of watering, the level of the soil mix should be ½ to 1 inch below the rim of the container. Label each container as it is planted. Include the name of the cultivar and the planting date. After potting, water each container thoroughly.
In order to bloom, tulips and other spring-flowering bulbs must be exposed to temperatures of 40 to 45 degrees Fahrenheit for 12 to 16 weeks. Possible storage sites include the refrigerator, root cellar or a trench in the ground. When using the refrigerator for cold storage, place the potted bulbs in a plastic bag if the refrigerator contains apples or other ripening fruit. Ripening fruit give off ethylene gas that may impair flower development. During cold storage, water the bulbs regularly and keep them in complete darkness.
Begin to remove the potted tulip bulbs from cold storage once the cold requirement has been met. At this time, yellow shoots should have begun to emerge from the bulbs. Place the tulips in a cool (50 to 60 degree Fahrenheit) location that receives low to medium light. Leave them in this area until the shoots turn green, usually in four or five days. Then move them to a brightly lit, 60 to 70 degree Fahrenheit location. Keep the plants well-watered. Turn the containers regularly to promote straight, upright growth. On average, flowering should occur three to four weeks after the bulbs have been removed from cold storage. For a succession of bloom indoors, remove pots from cold storage every two weeks.