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Bulb Planting: Why and How to Pre-Cool Flower Bulbs

Do I need to "pre-cool" my bulbs before I plant them? How does that work?


Spring-blooming bulbs need to be pre-cooled, or pre-chilled, in areas where the soil temperature doesn't cool down enough in the winter—generally USDA Zones 8, 9 and 10. Tulips, hyacinths and crocuses require pre-cooling here. To pre-cool bulbs, put them in the fruit/vegetable drawer of the refrigerator for 8 to 14 weeks. Don't store them with ripening fruit, though, which can give off ethylene gas, which damages the bulbs. Then plant the bulbs immediately in the garden or containers.

To avoid having to pre-cool your bulbs in regions with mild winters, choose bulbs that don't require it. These include daffodils and narcissus, iris, freesia, scilla, alliums and triteleia, among others. A good bulb catalog will indicate which selections are appropriate for warm winters and which require pre-cooling. Many bulb companies also offer pre-cooled bulbs; they will keep you order in cold storage and ship it to you at planting time (December or January in warm areas).

Image: Mariluna
Learn more about growing bulbs with Horticulture's Bulbs CD, a compilation of articles on bulb techniques, design and cultivation advice and favorite bulbs to grow.

Check out our two illustrated how-to downloads: Bulbs and Gardening with Bulbs & Tubers.

Plant bulbs fast and easy with Clarington Forge's Bulb Planter tool.

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