Bulb forcing can bring the bright colors and fragrances of spring indoors during winter. Daffodils, tulips, hyacinths, crocuses, and other spring flowering bulbs can be forced indoors from December through March.
Purchase bulbs from a local garden center as soon as they arrive in the fall. Bulbs are generally available from September through November. Bulbs also can be purchased from mail-order nurseries. They should be large, firm, and unblemished. So-called “bargain” bulbs and damaged bulbs may bloom poorly. Large, high-quality bulbs produce the largest, most attractive flowers.
Many different spring-blooming bulbs can be used for forcing, but some have better success than others. These species are typically the most successful for the home gardener.
- Tulip (Tulipa)
- Daffodil (Narcissus)
- Hyacinth (Hyacinthus)
- Crocus (Crocus)
- Grape Hyacinth (Muscari)
With a little more experience, these species are great ones to try next.
- Snowdrops (Galanthus)
- Dwarf Iris (Iris reticulata/Iris danfordiae)
- Siberian Squill (Scilla)
- Striped Squill (Puschkinia)
- Glory of the Snow (Chionadoxa)
- Windflower (Anemone)
- Lily-of-the-Valley (Convallaria)
Specific cultivar recommendations for some of these species can be found in this publication: Forcing Flower Bulbs
Spring-blooming bulbs will require a chilling period of at least 12 to 15 weeks to initiate a well-developed root system, stems, and flower buds. Additionally, they typically take 2 to 4 weeks to grow and bloom once removed from the cold treatment. This means that to have bulbs in bloom during winter, you need to plant the bulbs and start the cold treatment in early fall. Count back 14 to 19 weeks (chilling requirement + time to bloom) from the desired bloom date to determine the latest week you can pot the bulbs and start the cold treatment. For most bulbs, to have blooms in mid-December, potting should occur by the beginning of September. For blooms by Valentine's Day, potting should occur by mid-October.
While the bulbs need a minimum of 12 to 15 weeks of chilling time to come into flower, they do not have a strict maximum number of weeks they must be in cold storage. It is possible to pot all the bulbs at the same time in the fall and remove them over a 2 to 4 week period in the winter after the minimum 12 to 15 week chilling time has been met. This allows for a succession of blooms and more time to enjoy brightly colored spring flowers in winter.
Most bulbs are forced in a well-drained, commercial potting mix. Any type of container can be used for forcing as long as it has one or more drainage holes and is twice as deep as the bulbs to be planted.
The first step in planting is to partially fill the container with potting soil. Then place the bulbs on the soil surface. Adjust the soil level until the bulb tips are even with the rim of the container. Generally, 3 hyacinths, 3 to 5 daffodils, 5 to 7 tulips, and 10 to 12 crocuses will fit in a 6-inch-diameter pot. Forced bulbs typically look more attractive when planted densely - don't be afraid to place this close together in the container. Plant flat-sided bulbs, such as tulips, with the flat side facing the edge of the container. This allows the first leaves to form a border around the edge of the pot improving the appearance.
Once the bulbs are in place, add additional potting soil until the bulb tips show just above the soil surface. The level of the potting mix should be ½ to 1 inch below the rim of the container. After potting, water each container thoroughly. Water the newly planted bulbs from the top or partially submerge the pots in a tub of water until the soil surface is wet. Finally, write the name of the bulb variety (cultivar) and planting date on a label and insert it into each pot.
Different types of bulbs can be planted in a single container for a colorful indoor display. For example, crocuses or grape hyacinths can be planted in a container with tulips or daffodils. The larger bulbs are planted first and completely covered with soil. The smaller bulbs are then planted on top of the larger bulbs. While they may not all bloom at the same time, you will have color for several weeks.
Basic Steps to Planting Bulbs for Forcing
|1. Choose a container that has drainage holes and is twice as deep as the bulbs to be planted.
|2. Partially fill the container with potting soil.
|3. Arrange the bulbs on the surface of the potting mix. Containers are more attractive when planted densely. Avoid injuring the bulbs; don’t press them into the potting soil.
|4. Fill the container with additional potting soil to within 1-1/2 to 1 inch of the container’s rim. The tips of the bulbs should stick above the potting mix
After planting, the potted bulbs need to be exposed to temperatures of 40 to 45°F for 12 to 15 weeks. The bulbs will not bloom properly without the cold period. Critical root growth and flower development occur during this period. The best places for cold storage are a refrigerator, cool cellar, or outdoor trench. For best results, do not allow the bulbs to freeze. Water the bulbs regularly throughout the forcing period and keep them in complete darkness. Many plants begin sending up shoots before the cold treatment is complete. Be careful not to damage these shoots. If containers are stacked on top of one another, arrange them in a single layer to prevent shoot damage.
Do not chill bulbs in a location where fruit is being stored. Ripening fruit, such as apples, give off ethylene gas that can inhibit flower development and plant growth. If chilling in a refrigerator where apples or other fruit also are being stored, first place the potted bulbs in a plastic bag. During cold storage, remove the plastic bag containing the potted bulbs approximately once a month. Open the bag for 1 to 2 hours to allow for air exchange, then reseal the plastic bag and place it back in the refrigerator.
Annual flower beds and vegetable gardens are possible sites for outdoor storage and allow Mother Nature to provide the cold treatment. In late October or November, dig a trench that is at least 1 foot deep and wide enough to accommodate the containers. Place the pots in the trench, cover with straw, and place a tarp over the area.
After 12 to 15 weeks of cold storage, roots should be visible through the drainage holes. Also, yellow shoots should have begun to emerge from the bulbs. If the bulbs are at the proper stage of development after their chilling period, move the containers to a warmer (50 to 60°F) location that receives low to medium light. Leave them in this area until the shoots turn green, usually 4 to 5 days. Then move them to a brightly lit, 60 to 65°F location. Keep the plants well-watered. Turn the containers regularly to promote straight, upright growth.
On average, bulbs will flower 2 to 4 weeks after removal from cold storage. Smaller bulbs tend to come into bloom sooner than larger ones, but the number of weeks varies slightly based on the cultivar, light levels, temperature, and other environmental factors.
For a succession of bloom during the winter, remove a few pots from cold storage every 1 to 2 weeks.
Tulips, hyacinths, and most other spring flowering bulbs are usually discarded after forcing. Most don’t bloom again when planted outdoors and attempts to force them again are usually unsuccessful. Daffodils, however, are an exception. Many forced daffodil cultivars perform well when planted outdoors. Hyacinths forced in hyacinth glasses also should be discarded.
The care after flowering is important if attempting to save forced daffodil bulbs. After flowering, remove the spent flowers and place the plants in a sunny window. Water regularly until the foliage begins to yellow. At this point, gradually withhold water until the foliage withers and dries. Carefully remove the bulbs from the potting soil, allow them to dry for 1 to 2 weeks, then store them in a cool, dry place until fall planting. When planting outdoors, be sure to plant them at the appropriate depth for outdoor planting - typically a depth equal to three to four times their maximum bulb diameter.
Several types of bulbs, in particular hyacinth, can be forced without soil in a vase of water.
Vases and Containers
A special hourglass-shaped forcing vase (sometimes called a hyacinth glass) is often used to grow a single bulb. The lower part is filled with water and the upper part holds the bulb. Sometimes a container partially filled with marbles, pebbles, or gravel can be used. The water is filled to just below the gravel and the bulbs are placed on top. Whether using a forcing vase or pebbles, it is important that the bulb never sits directly in water.
Use Pre-Chilled Bulbs
Pre-chilled bulbs are available from garden centers or mail-order nurseries. If you cannot find pre-chilled bulbs, you can chill them yourself in the refrigerator. Place them in a paper bag in a location that is 40 to 45°F for 12 to 15 weeks. A refrigerator works well as long as you are not storing them with fruit. Ripening fruit, such as apples, give off ethylene gas that can inhibit flower development and plant growth. During the chilling period, check on the bulbs frequently to be sure they are not drying out or staying too wet. Remove any rotting or dried-out bulbs as soon as they are noticed.
Keep the Bulb Out of the Water
Place the pre-chilled bulbs in the container or vase and fill it with water so the water comes in contact with the small developing roots, but never touches the base of the bulb. If water touches the bulb itself, it will rot. Check the water level frequently and add water as needed to keep the roots in water (but not the bulb!). Monitor the water level carefully, especially in the first week as the water can quickly drop below the developing roots.
Fill with water as needed and replace water 1 to 2 times a week or when it becomes cloudy.
Rotate the vase frequently to promote straight upward growth and blooms should open in 2 to 4 weeks.
You made need to provide support for taller stems or blooms as they can easily tip in vases. One easy way to provide support for tall stems is to utilize a partially filled glass cylinder. By placing the bulbs on top of gravel and water in the bottom quarter of the cylinder, the leaves and stems can grow up and be supported by the upper half of the cylinder. Bulbs can also be buried in gravel to provide extra support, as long as careful attention is paid to not allow the water to come in contact with the base of the bulb.
After Bloom Care
Bulbs forced in water should be discarded after bloom.
- How do you force spring-flowering bulbs indoors?
- How do you force tulip bulbs indoors?
- How do you force daffodil bulbs indoors?
- What are some good daffodil varieties for forcing indoors?
- Are there any bulbs that don't need a cold period when forcing them indoors?
- Is it possible to save tulip bulbs that have been forced indoors?