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A Guide to Forcing Flower Bulbs

Spring-blooming bulbs are one of the most magical and anticipated treasures of the garden, appearing out of the bare ground to quickly offer color and signal winter’s end. Many of these same bulbs can brighten an indoor space months earlier if they are potted in fall and given the proper treatment. Here’s how to force spring bulbs into a winter bloom indoors.

Tricked into bloom in pots indoors, bulbs add color and cheer midwinter.

Tricked into bloom in pots indoors, bulbs add color and cheer midwinter.

Bulbs That Need a Cold Period

Some bulbs require a period of cold temperatures before they will bloom. These include tulips, hyacinth, grape hyacinth (Muscari spp.), crocus, daffodils and most other spring-blooming bulbs. Of these, tulips and daffodils are the most challenging, so if you’re looking for a safe bet, opt for crocus, hyacinths and others.

1. Select a wide, shallow pot in which to plant the bulbs, and get enough bulbs so that they’ll fill it when planted shoulder to shoulder. Ignore the recommended spacing for the bulbs; that applies for long-term plantings in the garden. Pots look best when crowded. Outdoor planting depth also does not apply to pots. The pot need be only deep enough to leave about two inches of root space beneath the bottom of the bulbs.

2. Add enough pre-moistened potting mix so that the tops of the bulbs sit within an inch below the pot’s rim when they are placed on the mix. Add all of the bulbs and cover them with more potting mix.

3. Move the entire pot to a cold area where it can stay for the recommended chilling period for the type of bulbs you’re growing. This can be anywhere from 10 to 18 weeks; here’s a helpful guide. The temperature in your chilling area should run between 35–45˚F, and it should be dark. This may be a cold garage or basement, an unheated but enclosed porch, a crawl space beneath the house or other cold but not freezing area. To simulate darkness in an area like an unheated porch or breezeway, just place a sheet of cardboard over the top of the pot. This will also allow you to stack multiple pots and save space. An extra refrigerator can also be used for storing potted bulbs.

4. At the end of the chilling period, place the pot in bright but indirect light at room temperature. Water lightly if the soil is dry. Within weeks the bulbs will begin to sprout. Once they have a couple inches of growth, move them into direct light. When they begin to bloom, indirect light and cool room temperatures will prolong the display. Discard the bulbs after they bloom, as they are unlikely to perform well again.

Bulbs That Don’t Need a Cold Period

Certain other bulbs do not require chilling before they will bloom. These include some of the most popular bulbs for forcing: amaryllis and paperwhite narcissus. They’re popular because they’re so easy.

1. Paperwhites and amaryllis can be forced in soil. Amaryllis should be buried only up to their shoulders, while paperwhites can go a bit deeper.

2. These bulbs will also grow and bloom if simply placed in a container of pebbles and water. Situate the bulbs so that the pebbles support them and their bottoms just barely touch the top of the water in which the pebbles sit. Roots will grow down into the water.

3. Place them in a dark, cool (ideally, 50–58˚F) spot for a couple of weeks, then move them into bright light and warm temperatures, where they will continue to grow and bloom.

4. Paperwhites generally bloom within four weeks of planting, while amaryllis can be slow to get growing. Expect amaryllis to bloom eight to twelve weeks after planting.