Forcing Hardy Bulbs Indoors
Many fall planted, spring flowering bulbs may be grown indoors to bloom during winter. Some of the most commonly indoor forced bulbs are small early tulip varieties, crocuses, daffodils, narcissus, and hyacinths. Pot these bulbs in a well-drained planting mix and containers with drainage holes. Plant the bulbs so that they are only half covered with potting soil. Allow for 2.5 cm (1 in.) or more of soil below the bulbs. For best results plant bulbs with same flowering time in same container.
Most hardy outdoor bulbs require a cool dormancy period at 3-10 C (35-50F) after they are potted. A cold room or an extra refrigerator can be put into use for this purpose. However, apples or cabbages must not be in the same area since they release ethylene gas which will damage flower buds. These bulbs require total darkness during dormancy; be sure to cover the bulb pots if they are located in an unheated porch or daylight-exposed area.
The length the cool period varies depending on the type and variety of bulb. The cooling requirements for some of the popular forcing bulbs have been listed below to help you with choosing compatible bulbs.
Name of Bulb |
Number of weeks to |
| Crocus | 5-8 |
| Grape Hyancinth (Muscari) | 8-10 |
| Freesia (tender summer bulb) | 6 |
| Hyacinth | 10-12 |
| Iris Danfordiae | 5-8 |
| Iris reticulata | 5-8 |
| Narcissus (except Paper whites) | 10-12 |
| Siberian Squill (Scilla) | 6-10 |
| Striped Squill (Puschkinia) | 6-10 |
| Tulip | 10-12 |
During the cool period keep the soil barely moist; check every week or so to make sure the soil does not dry out. If the bulbs are kept too wet the they can rot; dust bulbs with Bulb Dust before planting or soak them in a Benomyl solution to prevent such problems. Benomyl also controls the growth of mould on the soil surface.
Once bulbs show signs of shoot development move them into a warmer, 15 C (60 F), brightly lit location and keep the soil evenly moist. Warmer temperatures may damage the flowers. After the buds appear the pots may be moved into any light for display. After blooming bulbs can be discarded (they cannot be forced again) or saved for planting outside later in the spring.
Hyacinths can be forced in special hyacinth glasses which are filled with enough water to touch the base of the bulb. They will still need to be cooled in water-filled glasses for 10-12 weeks.
Amaryllis (Hippeastrum species)
These bulbs, usually associated with Christmas, can be easily forced to flower indoors. They produce four to six large flowers, 20-22 cm. (8-9 in.) on thick, hollow stems, in colours of red, salmon, pink, coral red and white or white and pink stripes.
Amaryllis should be planted in August to October for flowering during the Christmas season. Before planting, soak the base of the bulb in a shallow dish of lukewarm water for 12 hours. Pot the bulb in rich sandy soil to which bone meal or a complete commercial fertilizer (5 ml. or 1 tsp.) to a 15 cm. (6 in.) pot) has been added. Select a pot that allows for 2.5 cm. (1 in.) of space between the bulb and the edge of the pot. Set the bulb so that the neck and one-half of the bulb are above the soil surface. Firmly pack the soil around the base of the bulb. Keep the soil only slightly moist until the bulb starts to grow, thereafter keep the soil evenly moist.
Amaryllis
Keep potted amaryllis in a cool place until their roots are well developed. If you want an early bloom increase the temperature to 70-75 F when the leaves appear. After flower buds form feed these bulbs lightly with a complete fertilizer every two weeks throughout the blooming season. After the flowers fade cut them off. Remove the stems after they die, leaving at least 2 inches of stem on the bulbs. These plants will now produce large green strap-like leaves. During the summer they need a sunny location; they may be put outdoors. Sink the pots into the ground up to the rim and water and fertilize them like you would any sun-loving annual or perennial. Bring them indoors before the first hard frost. Gradually reduce the watering and place the bulbs in a cool dark room. When the leaves have withered cut them off. Allow the bulbs to rest for several months in a cool frost- free dark place until the first signs of growth appear then repot the bulbs and repeat the whole process.
Paperwhites (Narcissus tazetta)
These bulbs produce fragrant white daffodil-like flowers with very little effort at all. They cannot be grown outdoors but are popular indoor flowering bulbs. They do not require a cold dormancy period to encourage blooming. Plant these bulbs in pebbles in a shallow pan filled with water to just below the top of the pebbles, and they will bloom in a few weeks. Since they cannot be forced twice they are discarded after blooming. Other similar bulbs include:
- Chinese Sacred Lily - white and dark yellow
- Constantinopel - double white with orange centres
- Grand Soliel D'or - yellow