By James R. Feucht and James Klett, Colorado State University Cooperative Extension Specialists, Landscape Plants
If you want a rainbow of color in your garden next spring, start by planting bulbs this fall.
Bulbs purchased and planted in September will yield healthier blossoms in the spring. Bulbs purchased late in the season may have endured damaging storage conditions in garden centers and supermarkets. These bulbs usually will not perform as well as those purchased and planted early in the season.
When buying bulbs, look for the largest size within the type or variety under consideration. Sizes vary among varieties. Crocus, classified as a corm, but sold as a bulb, are small compared to the narcissus and many tulip bulbs. Some early flowering and species tulips are smaller than the hybrid cottage and Darwin types. Beware of differences between the metric and U.S. systems of measurements. Most imported Holland bulbs are sized by centimeters. Two-and-one-half centimeters equal an inch. Thus, a 5-centimeter bulb will be 2 1/2 inches in diameter -- a big difference.
Bulbs can be purchased from bulb catalogs, open bins and convenience pre-packs. Check the bulb's quality. This is easier to do when purchasing bulbs from an open bin rather than in packages. Check bulbs for bruising and mechanical damage and signs of mold or mildew. Don't consider bulbs that have produced green tips, an indication that growth already has started. One caution about buying bulbs from an open bin: They easily can be mixed together, and you could end up with bulbs you don't want. When selecting from an open bin, purchase bulbs that look like the others in the bin. Some slight color and shape differences exist among varieties. These clues will help you select correctly.
Decide where the bulbs will be planted and prepare the soil. Tuck bulbs into little spots here and there to add a splash of color in the spring.
Crocus creates a natural appearance around trees or in a rock garden. Species tulips bloom very early; they can be planted in with shrubs. You also can plant bulbs within a ground cover such as creeping juniper, but you may want to avoid most daffodils, because their foliage lasts so long through the season. You can cut the foliage of tulips, hyacinths and crocus sooner after the blooms have died down.
Bulbs do well in both sun and shade, but you may want to avoid hot, south exposures, particularly along the foundation of your home. Here the soil can warm up too early in the Spring, and the bulbs may emerge only to be killed back by freezing weather. South exposures also tend to dry over the winter resulting in poor bulb performance. A loose mulch, such as wood chips applied several inches deep after planting, will help. You can delay bulb emergence by mulching after the ground has frozen. Mulches insulate and keep the ground from warming up too quickly in the spring. Mulches also conserve moisture and prevent excessive weed growth.
Bulbs require a well-drained soil. Heavy clay soils usually are not suitable unless they have been amended with organic matter. Bulbs planted in poorly-drained soil are likely to rot or develop botrytis blight. Bulbs can be planted until late October, but September is best for good establishment. Plant bulbs deeper than seed, usually three to four times the diameter of the bulb. Be sure to plant them about 2 inches deeper in sandy soil.
Prepare the bulb bed by digging all of the soil from the area to be planted. Dig several inches deeper than necessary. (Planting guides, usually available from your garden center, suggest the ideal depth for each type of bulb.)
After soil is removed, add approximately one-third volume of compost or well-aged barnyard manure. Thoroughly mix these materials together, place the bulbs in the bottom of the pit according directions and backfill with prepared soil. It is not necessary to fertilize, as bulbs are storage organs that contain all the nutrients necessary for good root growth and shoot development. Fertilizers will not improve flowering ability, because the flower bud already is present in the bulb. If you've ever had bulbs that failed to flower, it was not due to lack of fertilizer, but rather that the bulb wasn't old enough or, for some reason, lacked a flower bud to begin with.
Water the area well and within a few weeks, the bulbs will begin to root. Keep the soil moist, but not soaking wet during this time. Then sit back and wait for a showy display of flowers next spring.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010