Bulbs

How Deep to Plant Bulbs to Protect Them From Freezing?

Ill.: 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: 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?!

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, laidbackgardener.blog will continue its mission of demystifying gardening and making it more accessible to all.

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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