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.
Bulbs, as a rule, are graded according to size expressed in inches or centimeters (a centimeter is equal to about 2.5 inches). In some lists the bulbs may be listed according to circumference, which is about three times the diameter. A bulb or corm having a circumference of 2.25 or 3.0 inches has a diameter less than an inch. For exhibition blooms, select the top or exhibition size. For garden beds, first or second size bulbs will be adequate and sometimes preferable. In tulips, select the second size for outdoor planting. The daffodil bulb is perennial so that the largest bulbs are the best. Bedding-size hyacinth are preferred for outdoor planting because their spikes are not so heavy and therefore are less likely to be marred by the battering winds of early spring. Do not buy cheap bulbs because they are either diseased or small or otherwise undesirable. Recommended sizes of bulbs are shown in the illustration, all drawn to the same scale.
Bulbs in the Flower Border:
Bulbs are very effective in the flower borders and flower beds, where they may take their place among the other flowers as a unit in the succession of bloom from spring to fall. They make the border colorful in early spring while other plants are making their plant growth, and die down and disappear as they are displaced by the other plants of the border. In the border, the bulbs should be massed irregularly in groups of six to twenty-five.
Bulbs Among the Shrubs:
Groups of bulbs may also be spotted in the shrub border. Clumps of the low-growing crocus and grape hyacinth, and the larger and more brilliant tulips and narcissus will be found very effective.
Bulbs in the Rock Garden:
The smallest types of bulbs may be used to good advantage in the rock garden. They should be planted in clumps beneath such rock plants as will not form a solid mat over the surface of the soil. They will make their contribution in color and fragrance in their season and then they will withdraw and be hidden by the later-blooming rock plants above them. Especially adapted for the rock garden are crocus, snowflake, snowdrop, glory of the snow, squill, winter aconite, dogtooth violet, grape hyacinth, coral lily, and Tulipa kaujmanniana.
Bulbs for Shady Spots:
Shady spots in the yard may easily be beautified by the use of narcissus, camassia, crocus, dogtooth violet, and many of the lilies. Of course, the soil in such places must be well enriched with plenty of good compost.