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?
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.
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
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?!