Proper site selection is critical for success with bulbs. The soil must be well-drained and attention given to proper light conditions (full sun for most bulbs).
Soil in bulb beds should be heavily amended with organic matter. Well-aged compost works well. Application of organic matter should be followed by deep tillage, at least 12 in. deep. The bed should be leveled and smoothed, but not packed. Just prior to or after planting, it is a good idea to add two or three inches of mulch (wood chips, bark, etc.) to the soil surface. It may also pay dividends to place some type of edging or border around the bed to slow encroachment of grass or other weeds.
Spring flowering bulbs should be planted in the fall. They require a period of cold weather to bloom and because these plants are generally hardy, the best way to provide cold is let them reside in the soil over winter. In Idaho , the best time to spring plant bulbs is late September through mid-October.
Summer flowering bulbs should generally be planted approximately one week after the last frost. To estimate the last frost date in your area, look at the Idaho chart compiled by Ed Hume Seeds. Some bulbs, such as caladiums and begonias will benefit from being started indoors 6-10 weeks before planting outdoors. They should not be taken outside until all danger of frost is past. In much of Idaho , this typically means 2-3 weeks after the last average frost date. Cornell University Suffolk County Extension has compiled a great discussion of planting and managing summer bulbs.
As a general rule, bulbs should be planted two to three times deeper than the top-to-bottom measurement of the bulb itself. Summer flowering bulbs may be exceptions to this rule and planting instructions should be provided on the purchase package. Planting density varies widely according to species and personal preference. Specific instructions for many species are provided in the Dutch Gardens web site. This site also provides pictures, descriptions, and cultivation techniques for many bulbs.
Before planting, an application of fertilizer should be made. Bonemeal or a high phosphate fertilizer should be placed in the planting hole, followed by the addition of a small amount of soil to prevent direct contact of the fertilizer and the bulb, then the bulb planted. This can be followed up with a small amount of a complete fertilizer (equal to 1 to 2 lb nitrogen per 1000 sq. ft.) at the time the plants emerge. Bonemeal should be used with caution around dogs, who are attracted to the scent and may dig up bulbs planted with bone meal.
Bulbs are planted in the spring (for summer flowering) or fall (for spring flowering). Most bulbs are planted at least 4-8 inches deep, depending on the size. Fertilization at this time is recommended with a product high in phosphorus. Bone meal is an excellent choice,
Another excellent resource is the University of Illinois Bulbs and More web site.