How Long to Chill Bulbs for Forcing
Chill hardy bulbs at 35 to 48F: hyacinths 12 to 15 weeks, tulips, daffodils, crocus, and grape hyacinth 15 to 17, snowdrops 10 to 12. Paperwhites and amar...
Published by ThriveThyme
forcing bulbs bulb chilling tulips hyacinths indoor bulbs
The Short Answer
Most hardy bulbs need 12 to 17 weeks at 35 to 48F before they will bloom indoors. Then they take 2 to 4 weeks in a warm room to flower. Paperwhites and amaryllis need no chill at all.
Pick a bloom date on the Bulb Forcing Desk and it counts back to the day to pot.
Chill Chart
| Bulb | Weeks of cold | Weeks to bloom after | Total weeks from potting |
|---|---|---|---|
| Paperwhites | None | 4 to 6 after potting | 4 to 6 |
| Amaryllis, Dutch-grown | None | 6 to 8 after potting | 6 to 8 |
| Amaryllis, South African-grown | None | 3 to 5 after potting | 3 to 5 |
| Snowdrops | 10 to 12 | 2 to 4 | 12 to 16 |
| Hyacinths | 12 to 15 | 2 to 4 | 14 to 19 |
| Squill | 12 to 16 | 2 to 4 | 14 to 20 |
| Tulips | 15 to 17 | 2 to 4 | 17 to 21 |
| Daffodils | 15 to 17 | 2 to 4 | 17 to 21 |
| Crocus | 15 to 17 | 2 to 4 | 17 to 21 |
| Grape hyacinth | 15 to 17 | 2 to 4 | 17 to 21 |
| Dwarf iris | 16 to 17 | 2 to 4 | 18 to 21 |
Cold weeks are from Penn State Extension. Weeks to bloom after the cold are from Iowa State Extension. Paperwhite times are from MU Extension and amaryllis times from Iowa State.
Why the Tables Differ
Extension tables do not all agree. Mississippi State lists shorter ranges, such as 11 to 14 weeks for hyacinths, 14 to 17 for daffodils, and 8 to 12 for grape hyacinth. Variety and the exact temperature both matter.
The best test is the pot itself. Start checking at the low end of the range. Roots poking out the drain hole and shoots an inch or two tall mean the bulbs are ready.
- Too little cold: Mississippi State notes late-flowering varieties come up with short stems.
- Too much cold: early-flowering varieties can get long stems. Still, Iowa State notes there is no strict maximum, so you can hold pots in the cold and bring a few out every week or two for a longer show.
Bulbs That Were Already Chilled
Pre-chilled bulbs from a store have some of the cold behind them. So do bulbs you kept in the fridge before potting. Mississippi State says to subtract those weeks from the chill time. The desk has a box for this.
Best Temperature
- MU Extension: 35 to 48F, with 40F ideal.
- UW-Madison Extension: start at 45 to 50F for the first 3 to 5 weeks, about 3 weeks at 38 to 42F, then about 35F for the rest. A fridge at a steady 35 to 45F also works.
- Keep the pots dark and the mix just moist.
- Keep fruit out of the same fridge. Ripening fruit gives off ethylene gas that damages the flower bud.
- A garage or cold frame works if it stays above 20F.
Sources
- Penn State Extension, Forcing Flowering Bulbs for Indoor Beauty
- Iowa State University Extension, How to Force Spring-Flowering Bulbs Indoors
- Mississippi State University Extension, Forcing Cold-Hardy Bulbs Indoors
- University of Missouri Extension, Forcing Bulbs for Indoor Bloom
- UW-Madison Extension, Forcing Bulbs
- Iowa State University Extension, All About Amaryllis
Next Steps
Step-by-step potting is in how to force tulips, daffodils, and hyacinths indoors. For quick holiday bloom, see paperwhites and amaryllis. Then plan it on the Bulb Forcing Desk.