Home Gardening Center Tip Sheet: Bulb Forcing Tips and TechniquesBy Sonia Uyterhoeven
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Forcing is a technique that imitates indoors the environment that bulbs encounter outdoors, thereby tricking them into flowering earlier. Most bulbs need a chilling or a cold treating period to flower successfully and put on their best show. Different types of bulbs require different chilling periods, generally between 12 to 16 weeks. Bulbs will perform well as long as they have had the minimum time that they need.
For chilling, the basic requirement is a cold, dark space where the temperature is below 50°F and above 32°F--generally 40 to 45°F is best. An unheated garage or a cellar is usually an ideal spot. Cold frames and window wells are also suitable; cover over the containers with dry leaves or several inches of straw and lay pine boughs on top to help insulate the bulbs. The vegetable compartment of your refrigerator is also a good option. Store the pot in a plastic bag with air holes punched in it and do not store with fruit such as apples that emit an ethylene gas which is harmful to their growth.
After the appropriate period of chilling time, the pots will start to show top growth and roots should be visible through the drainage holes. Bring the pots into a well-lit, unheated room of your house (approximately 50 to 65°F) for about a week. If your basement is the right temperature but not bright enough, fluorescent lights will do the trick. During this phase, you do not need direct sunlight, bright light is best--you are simply mimicking the arrival of spring with increased temperature and light. If light is coming from one direction, rotate pots every other day to keep flower stems straight. After this adjustment period you can bright them into a warmer area of the home, but temperatures in the 60s are best for the first three week until they are ready to flower.
Exposing bulbs to high heat too soon will cause the stems to flop, and the flowers may not open. In general, do not place bulb pots close to heating sources; the cooler the location, the longer the bloom.
Planting your bulb containers:
- Plant containers in September, October, and November.
- Select a pot that has drainage holes. If you would like to display your bulbs in ceramic containers with no drainage holes (cache pot), you can plant the bulbs in a plastic pot and slide it into the ornamental container when ready for display.
- Plant containers with a good commercial potting soil. All bulbs need good drainage.
- Since the bulbs are in the containers for such a short time, feeding is not essential. They generally have enough food stored in the bulb.
- Plant bulbs closely together in pots to create a full container, but give them enough space so that they are not touching each other. Plant bulbs with the pointed end facing upwards.
- Cover bulbs so that they are just below the soil surface. After you water, the soil level will settle so that the tips of the bulbs are just poking above the surface.
- Label your pots with the variety of bulbs and the time of planting.
- Water the pots thoroughly.
- Unlike clay (terra cotta) pots, plastic pots do not "breath." Water carefully so that they do not become waterlogged.
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Generous support for the Home Gardening Center has been provided by Kenneth and Ellen Roman.