How Deep to Plant Bulbs to Protect Them From Freezing?

Ill.: http://www.clipartmax.com, montage: laidbackgardener.blog

Question: How deep should I plant my bulbs (hyacinth, daffodils, tulip, etc.) so they don’t freeze?

Stephane Pratt

Answer: In fact, bulbs can tolerate freezing once well rooted. The important thing is to plant them early enough (at least 4 to 5 weeks before the ground freezes hard) so they can produce roots beforehand, because their growth starts in the fall, out of sight underground, then stops during the cold of winter before resuming in earliest spring, as soon as the soil begins to thaw.

Frost line depth in North America. Photo: http://www.adirondackalmanack.com

It would be illogical to try to plant the bulbs deep enough for them to completely free of frost. Throughout much of the spring bulb planting areas of North America, the frost line (the depth to which the ground freezes) is over 18 inches (45 cm)! In Canada, it’s generally over 4 feet (120 cm)! Even in mild Great Britain, you can also calculate 18 inches (45 cm) in most areas. Imagine the planting hole that would be needed to protect your bulbs from frost in Alaska! (And yes, gardeners do grow tulips, daffodils, etc. in Alaska.)

Follow the Rule of Three

Plant bulbs at a depth equal to 3 times their height and at a spacing equal to 3 times their diameter. Ill.: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux

Simply apply the “rule of three”* for most bulbs: plant the bulb at a depth of about 3 times its height. Thus, most of the larger bulbs will be about 6 to 8 inches (15 to 20 cm) deep and the smaller ones, some 3 to 4 inches (8 to 10 cm). This ensures that the bulb is well covered with soil when the soil begins to freeze.

*While we’re at it, the rule of three also applies to the spacing of the bulbs: space them at a distance equal to 3 times their diameter.

Moreover, if you don’t plant your bulbs deeply enough, they’ll move downwards in the soil. They have contractile roots that will pull them down, albeit gradually, to the appropriate depth for their species.

Ain’t Ma Nature wonderful?!

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “How Deep to Plant Bulbs to Protect Them From Freezing?

  1. Without frost, we just plant them deep enough to develop strong stems.

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