The Bulb Depth Rule Is a Ratio, Not a Fixed Number

Bulb planting depth guidance is expressed as a ratio — roughly two to three times the bulb's own height, measured from the base to the tip — precisely because bulb size varies so widely. A small crocus corm might be an inch tall, calling for a two-to-three-inch planting depth; a large daffodil or allium bulb can be two to three inches tall on its own, needing four to eight inches of depth to match the same ratio.

Planting too shallow leaves bulbs vulnerable to frost heave and rodent disturbance; too deep delays or weakens emergence since the shoot has further to travel using stored energy. Checking the specific bulb's height, not a blanket depth for the whole bed, keeps the ratio accurate.