The term “forcing” has always seemed a little harsh when referring to bringing flowerbulbs (tulips, hyacinths, etc.) into their flowering cycle prematurely in pots. “Enticing” or “tricking” seem more appropriate.
To trick or force flowerbulbs, we want to fool them into reacting as if they have already undergone the cooling period that bulbs planted in the ground experience over winter. To do this we need to pot them up and place them in a cool location for a long enough time to undergo the enzyme change within the bulb that causes the bulb to start its growth and flowering cycle.
It isn’t hard to do. Although any hardy bulb can be forced, some varieties are better suited to it than others. Very tall tulips, for instance, are not good candidates because they tend to get leggy and flop over when forced indoors due to lack of direct sun. Smaller and shorter varieties are the best candidates for forcing.
After selecting your bulbs, get some pots to use. Pots for forcing are generally shallow. They are referred to as “bulb pans.” For hyacinths, tulips, and daffodils a bulb pan about 6″ deep is perfect. Crocus, iris, and other smaller bulbs won’t need a pot more than 4″ to 5″ deep.
Place a couple of inches of soil in the bottom of the pot, then place the bulbs in the pot pointy side up. The bulbs should be placed very close together…even touching.
Then fill the pot the rest of the way with more soil and water thoroughly. Now your potted bulbs are ready for their cooling period.
They need to be chilled to 40 degrees or lower for at least three months. This can be done in an unheated basement, or in a spare refrigerator. It is also possible to chill them in the garden. To do this, dig a trench in your garden deep enough that the rim of the pot is at, or just below soil level.
Then fill in the trench around the pots with more soil. Cover your trenched bulb pans with mulch. Be sure that they stay moist. It’s OK if they freeze….that’s just they need. An inch or so of mulch on top and a couple of stakes so you can find them in mid-winter and you’re all done except for the waiting.
Starting in early February you can start bringing them in. It will take another 4 to 6 weeks for them to grow and flower. All over the country, greenhouse growers are planting bulbs in pots right now. They’ll put them into coolers and must pull them out at just the right moment so they’ll flower right in time for Easter. Timing is everything!
Forcing without chilling
There is one bulb you can force without the chilling period. Paperwhite narcissus are not a hardy bulb and can be forced without cooling them. For these, I like to use a glass containers filled with stones or glass chips or marbles so I get the added interest of watching the roots grow.
Simply nestle the base of the paperwhite bulb into the gravel, again placing the bulbs so that they are almost touching. Fill the bowl with water to just BELOW the base of the bulb. Don’t let the bulbs sit in the water since they might rot. Then, just step back and enjoy the show. Have fun!