How To Force Bulbs Indoors

Flower bulbs are particularly suited for an indoor cultivation with an early flowering. This is called “forcing” the bulb.
Here’s how to enjoy large, beautiful flowers in your home, even out of season.

Plants | Water | Gravel | Soil

Which plants are best suited?

flower bulbs
Forcing involves artificially recreating winter conditions to accelerate the flowering of the plant.
Most bulbs are well suited to this exercise. Those with a heavy gauge and short stems that are the most successful.
Depending on the forcing technique used, it is necessary to distinguish between:

  • Spring-flowering bulbs: amaryllis, hyacinths, tazetta daffodils, Armenian Grape Hyacinth, crocus, and tulips.
  • Summer-flowering bulbs: achimenes, curcuma, gloriosas, gloxinias, haemanthus, lachenalia, lilies, sprekelia vallota, veltheimia, and calla.

There are 3 ways to grow these plants by forcing them: in water (with a carafe), in gravel, or in a soil mix (potted).
The first two are the easiest to make, they require few resources and offer the finest aesthetic effect. However, they relate only to spring-flowering bulbs.
Be aware that forced bulbs will not be able to bloom again (save for the amaryllis).

Water – Carafe bulbs

water bulbs
Forcing bulbs in a carafe is a technique that dates back to the seventeenth century. The bulbs best suited for this task are hyacinths.
Unless otherwise stated, and for an implementation between mid-September and mid-November, the bulbs need to be prepared beforehand.
To do this, enclose them in a plastic bag and place them in the crisper compartment of your fridge for six weeks. They’ll be ready when they’re out of the fridge.
The thermal shock should not be applied to some bulbs, such as the amaryllis and hyacinths (in which case you can proceed to the next step).

Once the bulbs are out of the fridge, you can prep the carafe, filling it with water.
Place the bulbs inside the container.
Be careful that the bulb should never be in contact with the water, otherwise it may rot. Keep about an inch between the bulb and the water surface. Roots will emerge, attracted by the proximity to the water.
The pitcher must then stay in the dark between 50°F/10°C and 55.5°F/13°C, until the appearance of a shoot between 2.5 in/6 cm and 3 in/8 cm. You can then place it in any room in your house, with some natural light and a temperature between 60°F/16°C and 68°F/20°C.
Periodically readjust the water level. The flowers should show up a month later.

To prolong flowering, place your plant in a room where the temperature does not exceed 64°F/18°C. This applies to all bulbs grown indoors, regardless of the forcing technique used.

Gravel bulbs

gravel bulbs
The easiest forcing technique, and a good workshop for children, is using gravel.
Bulbs (except for daffodils and amaryllis) are prepared the same way as for cultivation in a water carafe (i.e. to be placed six weeks in the fridge).

For the container, all you need is a perfectly sealed pot. You can let your imagination run wild as to which one you want.
Line the bottom of the pot with coarse gravel (thickness between 1.5 in/4 cm and 2 in/5 cm).
Place the bulbs inside it, while ensuring they do not touch each other.

You can then fill the rest with gravel (without filling the pot up to the top). You want to cover in part the bulbs. Then add water, until it reaches the base of the bulbs.
When roots develop, they will set the bulbs in the gravel.
Until the shoots are between 2 in/5 cm and 2.5 in/6 cm, keep the container in a room without light, and a temperature between 50°F/10°C and 53.5°F/12°C.
Make sure the bulbs always have water. To prevent the water to languish, mix a few pieces of charcoal in the gravel.
After their stay in the dark, you can let them find some light and heat.

Soil – Potted bulbs

potted soil bulbs
For all bulbs, whether spring or summer, forcing them in a soil mix is the best solution to just enjoy an early flowering.

  • Here are the different steps:
  • Plant the bulbs in late January/early February. Provide a container with a water outlet, the bulbs do not like excess humidity.
  • Line the bottom of the pot with a drainage layer of about an inch.
  • Fill the pot with a permeable and aerated mixture: 1/3 garden soil, 1/3 sand and 1/3 compost. You can replace a third of the sand with garden soil if it is not that compact.
  • Tamp the mixture and sprinkle well with water before placing the bulbs.
  • Bury the bulbs two-thirds in.
  • Place the pot in a dark and cool room (a garage or basement, for example). Bury it in a larger container, between 6 in/15 cm and 8 in/20 cm of peat kept moist.
  • Dig them up after eight weeks. Yellowish shoots should be apparent. The pots can then be brought indoors, but must remain in the dark for a couple of weeks, at a temperature between 50°F/10°C and 60°F/16°C.
  • They can then be placed in the light at room temperature. Crocuses and hyacinths require a cooler temperature.
  • The flowers will bloom in 20 to 30 days.
  • Continue to provide them with light and plenty of water until October.
  • During the months from November to January, let the bulb dry completely, remove the foliage. Keep the bulb out of its container dry. Separate the bulbs before replanting.

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