Even though the majority of bulbs will grow in almost any kind of soil, practically all bulbous plants thrive best in a well-drained soil. In poorly drained soils bulbs deteriorate and finally disappear. While most bulbs will produce blooming plants in poor soil, many of them will give better results in good soil.
There are two general methods of planting bulbs. According to the first method, the bulbs are placed on the surface of the bed where they are to be planted, and then planted in an individual hole dug with a trowel. In placing the bulb in a hole made in this way, it is important that the base of the bulb be in full contact with the soil and not have an air pocket at the bottom. It is to avoid an air pocket that a trowel rather than the old method of using a pick or crowbar be used.
The second method, commonly used in formal gardens or large beds, consists in removing the top soil from the entire bed to a depth to which the bulbs are to be planted. Set the bulbs in place and shovel back the soil, being careful not to move any of the bulbs. This method can be used only where there are no perennials and involves a lot more work than necessary for home planting.
Depth of Planting:
Each kind of bulb, and in lilies each variety, has an optimum depth at which it should be planted. In general, bulbs should be planted from two to three times their own depth beneath the surface. In extremely light soils, bulbs may be planted somewhat deeper than in heavy clay soils. The depth of planting of each kind of bulb is shown in the accompanying illustration. The closer you follow this chart in planting, the better you will be pleased with the final results. Some bulbs are able to assume the right depth in the soil by means of "contractile" roots which, by becoming shorter and thicker, are able to pull the bulb or corm down to the correct level. It is in this way that seedling bulbs of some plants, as scilla, are able to travel from near the surface to several inches underground. In crocus the new corm is developed on top of the old each year, but the new corm is pulled down to the proper depth by the contractile roots.
Originally published in Organic Gardening, October 1949.