Forcing Bulbs for Winter

By Patricia Hanbidge

November 3, 2024

Key points from this story:

• Forcing bulbs can mimic spring bloom
• Choose large, healthy bulbs to plant
• Plant bulbs close together for display
• Chill bulbs for 12-15 weeks to bloom
• Avoid storing bulbs near produce
• After blooming, bulbs can be replanted

This is an annual autumn chore for me that is truly worth all the effort it entails…especially when I did not get all the spring flowering bulbs planted in the garden!

However, if you too have been caught with some extra bulbs - do not fret - many of the hardy spring-blooming bulbs can be coaxed to bloom by a process called "forcing". Tulips, hyacinths, daffodils, crocus, scilla and miniature iris are all easily convinced to bloom as long as a simple process is followed.

When choosing bulbs to "force" bigger is truly better. Ensure that large, healthy bulbs, free of blemishes are chosen. I prefer to use selections that will not grow very tall to ensure that little or no staking is required during growth. Use any clean container with good drainage for potting up your treasures. Allow about 5 centimetres or 2 inches of soil below the bulb. The top of the bulb should be placed approximately even with the rim of the container. Use a loose potting mix that will drain easily. (Bulbs whether inside or out do not like "wet feet".) Position the bulbs with the pointed end facing up. If you are planting tulips, place the flattened side of the bulb towards the outside of the pot. It is not necessary to add fertilizer as the nutrition needed for bulbs to grow typically comes from the bulb itself. Bulbs should be planted very closely together for forcing in order to give a more attractive display. Add enough soil to fill the pot, leaving the very tips of the bulbs exposed if you are planting daffodils or the smaller bulbs like iris, scilla or crocus. Plant tulips deep in the pot as they seem to push up in the pot quite strongly. Water thoroughly. Label the pot with the type of bulb planted and the planting date.

The next step in the process is to give these hardy bulbs a period of exposure to cold or stratification. This is an essential step to ensure your bulbs will bloom. A root cellar is ideal for this purpose, but any area that remains just above freezing works very well. If you do not have any area suitable for this cold period, a chilling period in the refrigerator will also work. Ensure you do not store bulbs in the crisper with fruits or vegetables, as they produce ethylene gas that will damage the immature flower buds. You'll need to maintain a temperature between 2 and 10 degrees C (35-48F) for approximately 12 to 15 weeks depending on the type of bulb planted.

Each type of bulb will have different requirements for both the cooling period and the growing period. A good rule of thumb is that the growing period is shorter for the smaller, shorter bulbs. Crocus, hyacinth and daffodils all require about a 12 to 14-week chilling period. Tulips and miniature iris need about 15 weeks of chilling to get good bloom. The single, early flowering, short stature tulips will show the most success.

Once removed from the cold, place your containers in a cool, sunny location away from heating vents and drafts. When the stem tips begin to colour, they should be moved out of direct light and placed wherever they are to be displayed. Prolong the bloom period by moving pots to a cool location each night, even into the refrigerator if space permits.

Best yet, when the bulbs have finished blooming, cut off the blooming stems and move the containers to an unused basement corner to let the foliage die back naturally and "feed the bulb". These can then be planted outside to enhance your outdoor landscape next year!