Every gardener has experienced the horticultural equivalent of having "eyes too big for one's stomach."
With me, it occurs quite regularly every fall when I fall victim to over-buying from some of Howard County's beautifully supplied garden centers or from the lush spring flowering-bulb catalog. After cramming every possible corner of the flower bed with the new daffodils and digging up yet more lawn space to accommodate those irresistible tulips, there are still leftover bulbs. The Yankee in me can't throw them out.
This predicament is how I arrived at learning how to "force" bulbs indoors for winter and extra-early spring blooming. I discovered that many of my leftovers could be potted up, given a cooling period mimicking Howard County winter conditions and then coaxed into bloom in January and February. The colors and scents of spring are a real spirit-lifter during that period when you think planting time will never come.
Among the easiest spring flowering bulbs to force here are the fragrant hyacinths. Certain types of daffodils also work. Only a few of the tulips -- mostly Triumph varieties -- seem to adapt to forcing at home. Small bulbs like crocus and iris reticulata are especially fun to try because so many of their tiny bulbs will fit into one pot, providing a real show.
Almost any pot will do, as long as it has good drainage. Commercial potting soil or a combination of garden soil, peat and/or sand is fine.
Just like bulbs growing outside, those grown indoors will drown and rot in soggy soil. The flower bulbs need the growing medium for good, firm anchorage even more than they need the nutrients it provides. (Almost all the energy the bulb needs to bloom its first year is already present in the bulb.) Plant as many bulbs per pot as will fit, with -inch between them and from the edge of the pot. The larger bulbs such as hyacinth, daffodil and tulip should be placed so that their tops (that's the pointed end!) are about even with the top of the pot, with all but the tops covered with soil. The smaller bulbs should be similarly spaced, but can be covered with -inch or so of soil. A good soak will eliminate air pockets around the bulbs. After letting the excess water drain through, place the whole pot in a plastic bag with holes poked in it and put in a dark, cool place (40-45 F is ideal).
The bulbs should stay in this pseudo-winter state for nine to 12 weeks, so an out-of-the-way place is best. Routine checking for drying out and for mildew are all that is required while the bulb develops a strong root system. Our basement garage serves this purpose for me, although temperature varies a lot there. A spare refrigerator is great if you have it. Those county gardeners lucky enough to have cold frames can forgo the plastic bag and put the pot directly in the frame. Cover well with a "blanket" of leaves, compost or soil so the bulbs won't freeze. The same method works in window wells, although you may be visited by hungry squirrels and mice who love crocus and tulip bulbs.
Although most of these bulbs look best when planted in groups of five or more in one pot, hyacinths are also attractive when planted singly. And the scent of just one in bloom will waft through several rooms.
After nine to 12 weeks of hibernation, the bulbs will have a significant root system and usually have begun top growth. At this point, the pot should be taken out of the dark and slowly introduced to lighter, warmer conditions. If you have several pots, some may be kept in cool storage a while longer for later forcing.
A gradual transition from this dark, cool environment to a warm, bright room is important. If it happens too quickly, long, gangly leaves with a few small flowers will result. A cold north window is good for the bulbs' first few days out, or use ordinary fluorescent lighting kept a few inches from the tops of the leaves. Ideal temperature is between 55 and 60 F.
When the stems and buds are well developed, (one to two weeks) you can move the pot to a sunny, warmer location. Ordinary house temperatures are fine. The plants can be kept in bloom longer by returning them to cool conditions at night. Remember the one day it took the outdoor tulips to bloom and die in last spring's heat wave?
Once the bulbs have been forced into early bloom, they will not do it again. Some people have success with letting the bulb foliage die down naturally, fertilizing regularly and then planting the bulbs outside. But these bulbs will take a year or two to regain the energy needed to bloom.
Tulips may never recover, so it is best to throw them away or add them to the compost pile.