How to Vernalize Tulips and Other Fall-Planted Flower Bulbs in Zones 8 & Above
Fall-planted flower bulbs such as tulips, daffodils, hyacinth, or crocus are wonderful additions to the landscape, but if you live in warmer winter climates (as in USDA zones 8 and above), these bulbs will need to be pre-chilled or vernalized before planting to successfully bloom. If you are in zones 4-7, your bulbs will receive enough natural chilling over the winter to bloom successfully and will only need to be dug up and divided every 3-4 years.
Spring-Blooming Flower Bulbs That Don’t Need ChillingSome bulbs do not need to be pre-chilled and here are some examples:
- Dutch Iris
- Scilla peruvian
- Paperwhites, Carlton, Erlicheer, Thalia, and Avalanche are daffodil varieties that can be grown without pre-chilling.
Bulbs that Will Need Pre-Chilling if You are in USDA Zones 8 and Above
Now for the flowers that need to be pre-chilled for about 3 months.
- Glory-of-the-Snow (Chiondoxa)
- Grape Hyacinth (Muscari)
- Iris reticulata
- Snowdrops (Galanthus)
There may be more varieties that need pre-chilling, but these are the most common.
How to Pre-Chill Your Bulbs
Use your refrigerator and dedicate a drawer or area to your bulbs and do not have any apples, or pears in the area as they emit ethylene gas that can be damaging to the flower bulbs. The temperature should be set to between 35-45°F. Never try to rush the process by putting the bulbs in the freezer. Remove the bulbs when they have gone through the chilling period but not before you are ready to plant. Note: Do not place them outside in the sun prior to planting.
What Happens If You Don’t Pre-Chill?
If you don’t pre-chill your bulbs and plant them a couple of things can happen. First, they may not flower at all or if they do flower they may be on short necks with incomplete flowers. If your bulbs come pre-chilled (some bulb companies pre-chill their bulbs-ours are pre-chilled), they should produce flowers the first year and be grown as an annual or you can dig them up in early fall and go through the pre-chilling process again, although successful flowering may be decreased.
Spring blooms are possible from some of our favorite bulbs, it may take a little more effort, but the pay off is worth it–a garden full of colorful blooms.