Combine bulbs and perennials to extend bloom

We usually think of using spring bulbs for ostentatious displays of color that an- nounce the arrival of spring. While no one can argue about the beauty of such plantings, spring bulbs have another use--one that's more subtle but just as useful in the landscape. By incorporating spring bulbs into mixed borders and other landscape plantings, you can extend the bloom season of perennial plantings with minimal maintenance, while adding colors, textures and forms not available with perennials.

This strategy works well because the needs and habits of flowering bulbs and perennials are similar in many ways. In certain other ways, they are different but complementary. One of The Netherlands' most famous landscape architects, Mien Ruys, expressed it this way: "The fundamental vitality and expression of bulbous plants receive an added dimension in combined applications." Thus, bulbs have a place in mixed plantings, not just the monocultures we so often see.

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Ruys' statement reminds us of the similarities between these two groups of plants. Perennials grow in nearly every climatic zone around the world, and a large percentage of them display excellent winter hardiness. In areas where consistent snow cover occurs, many marginally hardy varieties also can thrive. This also applies to practically all of the bulbous plants I discuss here and reinforces the complementary nature of bulbs and perennials. This should be no surprise considering that perennial and bulbous plants often occur side-by-side in their natural habitats.

Because naturalized bulbs require treatment similar to many perennials, they necessitate little extra effort. Naturalized bulbs enjoy an annual application of compost in fall, as do many perennials. Also, during the summer, when the bulbs have withdrawn underground, take care not to disturb them when you cultivate around them. In fact, you should leave them alone as much as possible, another characteristic they share with many perennial plants. Thus, naturalized bulbs often fit well, culturally speaking, in perennial plantings.

Extending the flowering period In a mixed planting, the bulbs will emerge first in the spring (though you can extend their flowering period into early autumn if you include tender summer-flowering bulbs that bloom along with perennials). Mixed borders usually peak in summer, when most perennials are in bloom. Although it is possible to use spring-flowering perennials to lengthen the overall flowering period, it makes more sense to leave this task to spring-flowering bulbs and focus on the perennial show during the summer. Bulbs provide a much greater variety of early season choices.

The bulb show starts early, with small species such snowdrop (Galanthus nivalis), winter aconite (Eranthis hyemalis), glory-of-the-snow (Chionodoxa murielae), Siberian squill (Scilla siberica) and Crocus (several types). Then come the narcissi, tulips and hyacinths, and finally the ornamental onions (Allium) in June, bringing an end to the spring-bulb season. A few exceptionally late bloomers include Alliums and lilies (Lilium) that flower well into the summer months.

A factor that enhances complementary plantings is the ability of bulbs to naturalize. Many types gradually multiply by self-seeding or producing bulblets that eventually grow into new plants.

Variety is virtually unlimited The herbaceous perennial plants are a group of unequaled variety. From early in the growing season until late in the year, perennials provide even greater variety than bulbous plants. Their growth habits vary widely, just as their flower colors and sizes do.

In contrast to bulbous plants, perennials do not usually die back quickly after flowering--they remain green. For this reason, take the decorative value of their foliage into consideration along with their bloom. In addition, some perennials remain green throughout winter (for example, Arabis caucasica). Others, such as Hosta, have highly attractive foliage and yet others have attractive flower stalks that retain ornamental value far into the winter season (for example, Achillea filipendulina).

Hemerocallis, Hosta and Astilbe probably are the three most popular perennials among landscapers, and they top the list for good reasons. They are tough, problem-free and adaptable to a variety of growing conditions. However, all three share a disadvantage: They do not provide any visual interest during the winter.

For those who want more from their plants, many perennials possess interesting features throughout the year. For instance, ornamental grasses that retain dead stalks in winter can create a beautiful contrast to the ice and snow and produce intriguing sounds and motions. Or consider evergreen ferns: They provide charm after other plants have gone dormant.

Considerations for combinations Effective combinations are not a lot of work to create, but they require careful planning. Although experience is still the best teacher, start with a few of the basic concepts:

* When combining various perennials, pay attention to plant qualities that provide a function (other than aesthetics) in the area you're planting. For instance, a planting of Phlox stolonifera under large rhododendrons looks much more attractive and natural than using bark chips but does basically the same job of covering the soil and keeping down the weeds. Grouping perennials around a tree, boulder or bird bath in a lawn reduces trimming and, at the same time, improves the appearance of the feature.

* Consider all ornamental aspects of plants, including their appearance during non-flowering periods and their overall growth habits. Because most perennials only bloom for a few weeks of the season, you should include plants with a range of foliage forms, textures, colors and heights. A well-balanced border should have several species blooming at any one the time, blended in such a fashion that foliage provides interest and contrast when the plants are not in flower. A rule of thumb is that, at any given time, 10 to 15 percent of the border should be in bloom. The remainder, of course, will consist of foliage. Because this amounts to 85 to 90 percent of the planting, the importance of using foliage to its best advantage is obvious.

* When combining perennials with bulbous plants, you have two basic options:

* Combinations in which the perennials and bulbs flower at about the same time. In this case, colors, obviously, play an important role and should complement each other. For example, Brunnera macrophylla, with its blue flowers, makes a lovely partner for white- or yellow-flowering narcissi. The Christmas rose (Helleborus orientalis) pairs beautifully with the striped squill (Puschkinia libanotica [scilloides]).

* Combinations in which the bulbs flower first, while the later-blooming perennials are in earlier stages of growth. The flowering of one type becomes a festive aperitif for the other, such as an opening cushion of Geranium (cranesbill) with the white-flowering Narcissus triandrus 'Thalia'.

In plantings where the bulbs and the perennials do not bloom simultaneously, the bulbs' colors and heights are not as critical. Nevertheless, warm yellow flowers are popular for these early display, perhaps as a harbinger of the spring sunshine that is on its way.

Perennials will overgrow and disguise withering bulb foliage. This is useful because you must allow bulb foliage to wither naturally before removing it if the bulb is to bloom again the following season. Later, you can use annuals to fill in around perennials such as poppies and Virginia bluebells that go dormant after blooming.

* Groups of plants can frame or otherwise complement others. Conifers enhance perennial borders and frequently are used as a backdrop for them. Likewise, perennials nicely complement woody ornamentals. A planting of gray or silvery perennials neatly delineates where the lawn ends and the ornamentals begin. Such designs give a sense of definition and perspective to the whole landscape.

Integrating perennials and bulbs in a holistic way achieves a natural unity of forms and types. You cannot create this effect by using just one or two groups separately and certainly not when you use bulbs alone.

Experiment with plant types and design styles. Do not expect perfection instantly and don't crowd your plantings. Allow several seasons for the plants to mature and fill in. After all, a landscape of any scale is always a work in progress.

Carol J. Sutton, of CJS Communications, Vancouver, B.C., is the U.S. and Canadian representative of Plant Publicity Holland.

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