Forcing Bulbs Indoors

By Valerie Podmore, CSU Extension-Denver Master Gardener since 2020

With the pandemic still lingering, many of us are staying at home which can give us a feeling of needing something to prevent cabin fever, and since we are pretty much finished up with the outdoor growing season, our thoughts turn to how to make our indoor space more plant-y and flowery. Forcing bulbs indoors is a great way to have flowering plants throughout the winter months to add some joy, color, and scent to our lives.

If you are like me, you’ve grown one of the more well-known winter bulbs, such as amaryllis, but not ventured into anything further. Let’s see if we can all learn to do this together!

Forcing bulbs is essentially a way of fooling the plant into thinking it’s spring so that it will bloom much earlier than normal. Many bulbs are bred for just this type of growing, but amaryllis, crocus, hyacinth, narcissus (daffodils and paperwhites), tulips and grape hyacinth are good bulbs to use.

Remember that different bulbs will bloom at different times so if you need to, ask the supplier, or pay attention to the bulb/plant information that usually comes with the bulb. Look for bulbs which are top quality, good-sized (bigger is better!) firm and free of mold or mildew. If the bulb has a paper-like covering just leave that, as it is normal.

You will want to use clean clay, ceramic or plastic containers which range from 6 to 8 inches deep with drainage holes. Use new potting soil (not garden soil) and fill your pot or container about 1/3 full. Place the bulbs in the soil with the hairy root end in the soil and the tips pointing up.

Handle the bulbs gently to prevent damaging them, but plant the bulbs close together. Add soil carefully making sure the bulbs stay upright, leaving the tips slightly exposed. Remember to consider the planting depth for the specific type of bulb you are working with. Finally, water the soil until moistened.

Now is the time to simulate the bulbs’ being in the ground over the winter, so you will want to give the bulbs a cold treatment of between 35-38 degrees Fahrenheit for a period of 12-16 weeks. Unheated locations such as a basement, cellar, cold frame or even a fridge work great. Cover the pot with plastic that has holed poked in it if you choose to go the fridge method.

Don’t let the bulbs freeze and rely on the supplier information to tell you how long the bulbs should be chilled. It all depends on type and size. Having said that, paperwhites (a type of daffodil) are one bulb that don’t require this chilling method.

Next step after you’ve been so patient, is to bring the bulb containers indoors! Find a warm location (about 60-65 degrees Fahrenheit) that receives indirect light and place them there. You should start to see shoots in about 3 to 4 weeks. Don’t forget to keep the soil moist as the bulbs start to bloom.

Once the bulbs are blooming you can move the containers to a cool location overnight to prolong flowering. Many of these forced bulbs will not be able to flower again next season due to the amount of energy it takes to produce blooms. The forced bulbs can be composted once they have finished blooming. Having said that (again!), amaryllis are a type of bulb that CAN be grown to bloom year after year.

While we may need to start the process of forcing bulbs earlier in the year than December, there’s no reason we can’t give it go now and see what happens. You can always check with local garden centers or other suppliers to see what they have left, or even use any bulbs you didn’t get planted in the ground. Have fun and enjoy the flowery reward!

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