Planning a Bulb Garden

Any garden designed specifically to showcase bulbs requires special planning, otherwise there will be short bursts of flowering followed by long periods with no bloom.

Bulbs are classified according to their flowering season: late-winter and spring flowering, summer flowering, and fall flowering. Within each seasonal group, there are early, midseason, and late bloomers. Among spring-flowering bulbs, for example, late-winter flowering bulbs, such as snowdrops and Iris reticulata, are followed by early spring bulbs such as Dutch crocus, and Siberian squill.

By mid to late season such bulbs as narcissi and tulips are blooming, which are finally followed by very late season bulbs such as alliums. Within each bulb category, there are further divisions. Tulips, for example, are available in early, midseason, and late varieties. In the same way, among the summer bloomers, there are early, mid-season, and late lilies. In fact, a bulb garden composed of only lilies can bloom right through the summer if care is taken in selecting varieties.

One advantage of bulbs over many other garden plants is their adaptability. Although most bulbs prefer full sun or only light shade, their leaves generally sprout in early spring before deciduous trees and shrubs leaf out. Thus, some bulbs, specially spring bloomers, can be grown successfully in spots that are shady much of the year. Just about any soil is acceptable, although a generous addition of organic matter to poor soils is wise.

The only thing bulbs will not tolerate is waterlogged soil. If your chosen site stays moist or wet for long periods, consider planting bulbs in raised beds so they get the drainage they need. Bulbs can also be easily grown in containers as long as the containers are placed where they will not freeze solid during the winter.

Most hardy bulbs (lilies are a notable exception) lose their leaves in early summer, so it is important to plan ahead to fill in the gaps. Clusters of annuals and perennials, for example, can be interplanted among groups of bulbs. Ground covers and bulbs make an even better marriage: Bulbs will grow right through the ground cover, bloom, then disappear from sight until the following year. Choose an open, shallow-rooted ground cover to minimize competition with the bulbs.

Bulbs look best planted in groups rather than scattered randomly through the garden or planted in straight rows. Clusters of at least 3 to 5 large bulbs such as lilies; 7 to 10 medium-sized bulbs such as tulips, narcissi, or hyacinths; and 12 or more small bulbs such as crocuses or Siberian squills are fine. Avoid mixing bulbs: They rarely give an interesting display. Leave spaces between each cluster of bulbs to interplant ground covers, annuals, or perennials, which will help cover up the foliage of the bulbs as they fade.

Usually, tall-growing bulbs are planted at the back of the border or in the middle of the bed with smaller bulbs in front and medium-high ones in between. But it is also possible to grow bulbs of all sizes in a single space. Tall bulbs need deep planting, so put them in first. Then add a layer of soil, and place medium-high bulbs directly over them; finally, another layer of soil and then small bulbs. Since small bulbs flower first, the same spot will offer a succession of bloom. A good combination would be early crocuses, midseason hyacinths, and late tulips.

Massive formal plantings of spring bulbs, as commonly seen in public gardens, are also possible in the home garden but require some effort. In such cases, a hundred or more of the same bulb may be required to fill the bed. After blooming, either treat the bulbs as temporary visitors -- composting them and replanting the bed with summer flowers -- or remove the fading bulbs to an out-of-the way spot where they can ripen. They can then be replanted in the formal bed the following autumn after the summer flowers have finished their display.

The most beautiful bulb gardens often are not formal beds or mixed borders but naturalized plantings. In such cases, bulbs are chosen to suit the present conditions and are then planted permanently so they seem to have always been part of the landscape. In such cases, the elaborately colored, fully double hybrid varieties are usually forsaken for bulbs that more closely resemble wildflowers. Bulbs that are inherently tough and spread on their own are ideal choices.

Obviously, rigidly formal plantings are not recommended for naturalized gardens. In fact, one common planting method is to toss bulbs into the air and plant them where they fall. Another method is to lay out a garden hose in an irregular pattern that resembles a meandering stream and then plant bulbs within its limits.

People who enjoy multiplying plants find most bulbs to be obliging: They increase in number on their own. Any time you have to disturb a bulb, you'll find numerous bulbs of various sizes where the original bulb was planted. The largest ones can be replanted immediately and will bloom the following year; the smaller ones can be replanted or grown in an out-of-the-way spot for a few years until they reach flowering size. Naturalized bulbs will also multiply prolifically, although it may take several years before the seedlings reach flowering size. Rhizomes, tubers, and tuberous roots can also be divided by cutting them into sections. Each section must have at least one eye.

The discussion has focused on hardy bulbs, but there is a wide variety of tender bulbs. These are hardy only in the warmest parts of the United States. Elsewhere, they are either treated as annuals and allowed to freeze in the fall or dug up and stored indoors in a cool and dry but frost-free spot over the winter.

In the next section, we'll talk about bulb definitions.

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Gardeners tend to refer to any plant with an underground storage organ as a bulb, but there are actually many different categories.

True bulbs are made up of modified leaves that are attached to a flat basal plate and that surround the following season's bud. Many true bulbs, such as tulips and narcissi, are surrounded by a papery outer tunic. In others, such as lilies and fritillarias, the bulb is covered by fleshy scales.

Corms look like bulbs on the outside, including the flat basal plate and the papery tunic. But when they are cut open, they have a solid starchy interior stem. Crocuses are an example of typical corms.

In the final section, we'll define tubers and rhizomes.

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Tubers and rhizomes share many similarities with true bulbs and corms, but they do have some key differences.

Tubers are modified stems with starchy interiors but no basal plate or tunic. Both roots and shoots sprout from the same growth buds, called eyes. The potato is a typical tuber. Tuberous roots are similar to tubers but are really swollen roots. Dahlias produce tuberous roots.

Rhizomes are thickened underground stems. They grow in a horizontal direction, sprouting new sections as they go. The bearded iris (Iris germanica) has a typical rhizome.

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