Forcing Spring Flowering Bulbs
Are you looking forward to spring blooming bulbs? It turns out there is a way to “force” bulbs to grow and flower when you want them to. At the Smithsonian Gardens Greenhouse Facility, we have been forcing flowering bulbs for decades, although the practice has been in use since the 1800’s. The process starts with selection of the variety of flowering bulb (usually Narcissus or Tulips) by the Smithsonian Gardens Interiors team along with a finish date. The Production team then counts backward approximately 14-16 weeks from that date, which is usually late October or early November of the previous year. For example, we planted Tulips and Narcissus on November 14, 2022, with a finish date planned for March 8, 2023.
Once the bulbs are planted in 4” or 6” pots, they are watered thoroughly and placed inside our walk-in cooler at 45-55 degrees F. We then wait about 2 to 4 weeks until we see roots poking out of the bottom of the pots. The temperature is then lowered to 35-40 degrees F for the remainder of the cooling period. The goal of this temperature manipulation is to trick the bulbs into thinking that they are going through the natural fall/winter/spring temperature progression. Two weeks before the finish/installation date, the bulbs are moved into a greenhouse that mimics typical spring temperatures with 68˚F days and 63˚F nights. They are watered with a calcium-based fertilizer and drenched with a plant growth regulator to protect them from stem topple. These bulbs will start growing their “blooms off” as soon as they experience the warm greenhouse temperatures! Once the bulbs start to bloom, they will be shipped to their display location.
If you are forcing bulbs at home, use pots with holes in the bottom to allow for drainage. Plant the bulbs (4-5 Tulips or 3 Narcissus together) in a 6” pot that is three-quarters full of soil. Cover the bulbs with enough soil to blanket their necks slightly, and water enough where water drains from the bottom of the pot. Then place the pot in your refrigerator, a cooler in an unheated garage, or buried outside in a leaf pile. After about 14-16 weeks, remove the pots from their chilly environment, put them in a sunny location, and enjoy! They should flower within a couple of weeks. Next year, get a jump on spring with this fun process!