Forcing Spring Bulbs

Mary Heie, Extension Master Gardener in Anoka County, November 25, 2015

Sometime after Christmas, nurseries will be featuring pots of spring bulbs that have been forced to flower indoors. Why not try this yourself?

Choose your favorite bulbs: tulips, daffodils, hyacinths, crocus, sillas, and grape hyacinths (muscari). Use good sized, top quality bulbs. If using tulips or daffodils, choose shorter varieties because the stems and leaves of taller varieties may flop over. Use plastic or clay pots that have drainage. These can be put in a decorative cache pot after the bulbs start to grow. Ordinary potting soil works well, but if you choose to mix your own, use garden loam and peat moss, three parts to one. Do not use ordinary garden soil from your backyard garden. There is no need to add fertilizer as the bulbs have enough food stored in them for one flowering.

Plant the bulbs close together and leave the pointed end (“noses”) exposed. How many can be planted in a pot? As an example, a 6-inch pot will hold 6 tulips, 6 daffodils, 3 hyacinths, 15 crocus, or 12 to 15 sillas and grape hyacinths. Tulip bulbs have a flat side that should be planted facing the rim of the pot because they produce a large leave that tends to lay flatter than the other leaves. Planting this way will make the pot look nicer. When planting, do not pack the soil and leave some space for watering. There is a special glass vase that is designed for a single hyacinth. It does not require soil and allows only the roots to reach the water.

Water the pots well and place them in a plastic bag with some breathing holes punched in it. The cold treatment comes next. The pots must be given a cold treatment for approximately 12 weeks in temperatures of 35 to 48 degrees. Refrigerators work very well for this. Any unheated area in a house or even cold frames with soil and mulch will work as long as the bulbs remain at the right temperature and do not freeze. Record two dates: when the cold treatment is started and when the pots are ready to be brought out.

After you bring them out, put them in a sunny location with a temperature of about 50 to 60 degrees. They can be moved to a warmer location after the bulbs have started to sprout. Once the bulbs have started blooming, they will last longer if they are placed in a cool location at night. Since different varieties of bulbs take different amounts of time to flower, the “older” advice was not to mix varieties in a pot. However, professionals have discovered that different varieties can be forced to flower at the same time by placing newspaper (two or three sheets) over the pots for about a week when they first come out of cold storage and begin to grow.

After the bulbs have flowered, the food stored is used up. Therefore they will not bloom again indoors. However, if kept alive and planted outside in the spring, they may flower again in a year or two, the time it takes to restore food to the bulb.

For more information, see: http://www.extension.umn.edu/garden/yard-garden/houseplants/forcing-bulbs-for-indoor-beauty-in-winter