Tulips, hyacinths, daffodils, crocuses and grape hyacinths can be forced into bloom inside during the winter, and with proper planning it is possible to have a continuous supply of blooms from late January through April.
Use 6-inch pots and plant three to six tulip, hyacinth or daffodil bulbs, or seven to 15 crocus bulbs in each one. Extra-short bulb pots are best.
Use a mixture of one part topsoil, one part peat and one part sand. The mixture anchors the bulbs and serves as a moisture source. Thus, it must be well-drained and yet retain sufficient moisture. Fertilizer should not be added to mixture.
Use only top size No. 1 bulbs for forcing, preferably those sold for that purpose. The very earliest to bloom are the "prepared bulbs" - those that have been subjected to cool refrigeration. They may bloom from Christmas on. These prepared bulbs are recommended for planting in Southern and California gardens where the very minimum amount of cold is all that can be expected.
The bulbs need the cold in order to break dormancy and develop a root system.
Tulips should be planted with the flat inside of the blub against the inner side of the pot. In this way the largest leaf grows over the rim of the pot making a more attractive display.
It is most important that when the bulbs are planted they are not forced into the soil. Put them in the pot and cover them with soil so that only the tip of the bulb is exposed. Then water thoroughly to settle the soil.
Then store the bulbs in a dark, cool (35 to 48 degrees F.) place, such as your cellar to garage. A cold-frame can be used, or dig a trench and put the pots in it and cover them with 6 to 9 inches of straw, hay, leaves or some other similar mulching material. Any place that is dark with suitable temperatures can be used. If it gets too cold, the bulbs may be ruined, and if it is too warm quality will be affected.
They must be stored for a minimum of 13 weeks. During this period, water them when the soil becomes dry.
After the cold treatment has been completed they can be brought into the house, a few at weekly intervals.
The plants require three to four weeks to bloom. The best temperature for blooming is 60 degrees; keep them out of direct sunlight. Since the bulb contains most of the food it needs, it is not necessary to fertilize.
Bulbs that have been forced indoors are usually of little value for planting in the garden later on.