By forcing bulbs, you can have pots of blooms in your home in winter, because bulbs are storehouses containing embryonic leaves, stems and flowers. It is best to choose crocus, iris, hyacinth, muscari, narcissus and tulip varieties that are suitable for forcing. Use only healthy, firm, undamaged bulbs. You can stagger your planting from early October to late November.
How to grow bulbs indoors
- Use all-purpose potting soil or a porous artificial soil mixture.
- Plant the bulbs in low pan- or azalea-type pots of whatever shape and diameter you like. Usually 1 to 20 bulbs are planted per pot, depending on the type and size of the bulbs and the diameter of the pot. Use containers with drainage holes, because the bulbs may rot if they are kept too wet.
Type of bulbs
10 cm pot
15 cm pot
Crocus 5 to 6 10 to 12 Iris 9 to 12 18 to 20 Hyacinth 1 3 to 5 Muscari 6 10 Narcissus - 3 Miniature Narcisse 2 5 Paperwhite Narcisse - 5 Scilla 5 to 6 10 to 12 Tulip 3 6 to 7
- Cover the base of the pot with enough potting soil so that the tip of each bulb will be exposed once the container is filled. Arrange the bulbs side by side, but not touching. For tulip bulbs, place the flat side of the bulb facing the edge of the pot, so that the largest leaf will grow outwards. Add soil around the bulbs and tamp the mixture down, without compacting it. Continue until the pot is full.
- Water the soil and place the pot of bulbs in a cool, dark spot (about 4°C), such as a garage or coldroom where the temperature does not drop below freezing, a refrigerator with an average temperature of 4 to 5°C, or outside near your home’s foundations in a spot protected from freezing and thawing. The soil must not be allowed to freeze during this period, when the roots are forming. This stage takes 13 to 24 weeks, depending on the variety of your bulbs.
- Crocus: 13 to 20 weeks of chilling
- Iris: 13 to 19 weeks of chilling
- Hyacinth: 13 to 18 weeks of chilling
- Muscari: 14 to 20 weeks of chilling
- Narcissus: 15 to 24 weeks of chilling
- Scilla: 15 to 18 weeks of chilling
- Tulip: 14 to 20 weeks of chilling
- After this period, move the pots into a room with bright light and a temperature of 13°C to 16°C for 10 to 21 days.
- Place them on a sunny windowsill as soon as the shoots are 10 to 15 cm high.
- Move the pots out of direct sunlight once the flower buds have coloured. Keeping them in bright light and cool temperatures will extend their blooms, which should last for 7 to 10 days.
- Remove the flowers after they fade, and allow the foliage to dry naturally. Leave the bulbs in the pot, store them in a cool place and plant them outdoors in autumn.
- Bulbs will probably not flower if you try to force them two years in a row. They need time to build up new stores of nutrients.
- You can buy some bulbs that have been pre-chilled. They can be forced in water.
- There is no need to fertilize bulbs, because they contain all necessary nutrients.
- Store any bulbs that you are not ready to plant in a cool (17°C), well-ventilated spot, in cardboard boxes or open paper bags. Avoid plastic bags, which retain moisture and increase the risk of rotting. Your bulbs will bloom from January to April depending on the variety and when you plant them.
Reference: Holland Bulb Forcer's Guide, available at the Jardin botanique de Montréal library, for consultation only.