How to Grow Hardy and Tender Bulbs

Bulbs are the epitome of nature's talent for packaging, containing within themselves all of the essentials they need to grow and flower. Some don't even require soil — just witness a paperwhite narcissus blooming happily indoors in nothing more than a bowl of marble chips. But it is outdoors that bulbs really shine. Most are hardy and undemanding; some will even naturalize and provide color year after year. Whether for borders, cutting gardens, containers, rock gardens, or naturalistic plantings, bulbs deserve a place in every garden scheme.

Generally, bulbs are divided into two categories: the spring-flowering types, which are typically planted in the fall; and the summer-flowering bulbs, usually planted in the spring. Lilies (Asiatics, Orientals, tigers) are an exception to this rule; they can be planted in either spring or fall for summer blooms.

Another crucial consideration is whether the bulb is hardy or tender. Hardy bulbs (daffodil, crocus, hyacinth, tulip, lily, etc.) will survive the winter right in the ground to bloom again the following year. Tender bulbs (gladiolus, canna, dahlia, etc.), will also flower year after year, but in cold climates they must be dug up or "lifted" in the fall, stored indoors over the winter, then replanted the following spring.

Naturalizing Hardy Bulbs

A naturalized planting is one of the most popular uses for bulbs in the landscape. Instead of planting the bulbs in a formal bed or border, you scatter them in irregular groupings across an area of lawn or meadow, or at a woodland edge. For the most natural effect, avoid planting bulbs in straight lines or discernible patterns.

Naturalizing bulbs in your lawn works well with the smaller, daintier flowers like crocuses, puschkinia, squill (Scilla), grape-hyacinth (Muscari), or snowdrops (Galanthus). These bulbs flower early in the season and their foliage dies back fairly quickly. If you plant such bulbs in a lawn, don't mow until the foliage has yellowed and died back. At this point, the plant will have stored all the food it needs in the underground bulb to produce next year's bloom.

Most bulbs appreciate well-drained soil and sunlight. Keep in mind, however, that bulbs that flower early in the spring will have bloomed and faded long before deciduous shrubs and trees have begun to leaf out. So think of spring-blooming bulbs much like spring wildflowers. A fairly open woodland setting or orchard makes an ideal setting, particularly for long-stemmed showy ones like daffodils and early tulips, which can be seen and admired even at a distance.

Some bulbs need to be divided. For example, daffodils multiply enough to form dense clumps, which compromises the flowers. Dig after flowering (while you can still find them), divide the clumps, and replant immediately or store until fall.

For all bulbs, including larger daffodils and tulips, don't remove or mow over the spent foliage until it has withered naturally. For this reason, it's best not to plant these long-standing bulbs in a lawn or other formal area, where the dying foliage can cause an unsightly mess. Try planting these bulbs in a field or meadow, or somewhere else that you only mow once or twice a year. Or plant them at the base of deciduous shrubs or in mixed beds or borders where later-blooming plants will draw attention from the spent foliage.

Pre-chilling and Forcing Bulbs

Nearly all hardy, spring-flowering bulbs require a period of "chilling" or cold dormancy before they will begin to grow and bloom. For gardeners in most regions of North America, providing this cold treatment is easy. Simply planting the bulbs in the fall and leaving them alone over the winter provides plenty of cold treatment. Just make sure to select bulbs that are hardy in your growing zone.

However, people who live in very mild winter regions (Zones 9 and 10) must select their bulbs very carefully. Daffodils should be planted in December or January (the coldest time of the year), but other hardy bulbs, such as tulips, crocuses, and hyacinths, may require special treatment in mild-winter areas. Gardeners in these regions of the country should select from among the many varieties that are rated best in warm spring and summer conditions.

Many tulips will grow well as annuals in the South if the bulbs are prechilled. Other good bulbs for warm climates include crocuses, hyacinths, lilies, muscari (grape hyacinth), colchicum (autumn crocus), and alliums (ornamental onions).

The easiest way to prechill bulbs is to store them in the refrigerator, where temperatures can be easily maintained at 40 to 45 degrees F. Store them in breathable mesh bags, like the ones they are often sold in at garden centers. Then, when they have chilled for the requisite number of weeks, simply remove the bulbs from the refrigerator and plant them either outdoors in the ground or in containers.

If you have enough space in the refrigerator, you can even plant bulbs right in their containers and remove the whole pot at the end of the chilling period. Either way, place containers of bulbs that you're forcing into a warm, sunny spot and then sit back and wait for the bulbs to send up their green leaves. After their blooming period is over, you can continue to water the pots, letting the foliage die down naturally, then replant the whole mass of bulbs in the outdoor garden.

The most popular bulb for winter forcing is undoubtedly the paperwhite narcissus, which requires no period of prechilling before it will blossom. However, you can also add variety and color to your winter or early spring displays by prechilling many other types of bulbs, then forcing them in containers for indoor bloom.

It's common for florists to sell containers of forced bulbs that are all of one type, such as dark purple or pink tulips. This makes a smashing display, but you can also be creative by forcing several kinds of bulbs of different colors or even different species to make a mixed display.

Unless you're using a large container or you have a good eye for natural design, it's best to experiment with only a couple of types of bulbs in each pot. Plant bulbs that grow to roughly the same height and whose flowers will complement each other in form and color (pink alliums and white Dutch crocuses, for instance).

Pots sold for forcing bulbs tend to have no holes in the bottom, because many people grow paperwhite narcissus in a medium of small stones instead of soil, and so drainage is not an issue. It is possible to grow other bulbs this way as well, but keep in mind that you probably won't be able to replant them outdoors after they have blossomed unless you grow them in soil. When forcing bulbs in potting soil, make sure the container has drainage holes in its bottom and that you place a dish underneath it to catch the excess water, as with any other houseplant.

Tulips

Although tulips are technically considered perennials, many gardeners find that their bulbs are relatively short-lived and begin to decline over two or three years, producing smaller flowers and eventually dying out altogether. Unless your climate and growing conditions are ideal (hot, dry summers, cold winters, and well-drained soil), it can be difficult to coax some varieties of tulips into making a long-term commitment to your garden.

However, there are other types that, when given a little special care, will flower repeatedly and actually increase in size and beauty. These varieties are commonly known as "perennial tulips." Although there are other tulips that will put in an appearance reliably for years, this type contains many of the most highly recommended varieties. One note: When buying Darwin hybrids, keep in mind that the ones with deep color will naturalize better than those with pastel colors.

To create the best conditions for perennial tulips, top-dress the planting bed with well-rotted cow manure, or add a slow-release fertilizer in the fall (9-9-6 or lower profile). After the flowers have finished blooming in the spring, deadhead the spent blossoms and allow the foliage to mature and wither naturally, so the bulbs can gather energy for next year's bloom.

Lilies

Lilies are no more difficult to grow than other hardy bulbs, so long as you keep in mind a few of their important differences.

Plant lilies as soon as you get them, either in the fall or the spring. Because the bulbs lack the papery covering (known as a "tunic") that is common to other hardy bulbs, they can dry out quickly in storage.

Even more than other bulbs, lilies demand well-drained soil. Although lilies should be planted at a depth of 6 inches, you should till the soil to a depth of at least 12 inches, remove rocks and add organic matter such as leaf mold or peat moss to improve both the soil’s structure and drainage. Like other bulbs, lilies appreciate a little bone meal scratched in at the bottom of the planting hole, but do not really require other fertilizers at planting time. Instead, wait until the bulbs send up green leaves and then sprinkle a complete organic fertilizer around the plant and water it in.

Spread an organic mulch around lilies to help keep the soil moist and cool; use compost, well-rotted manure, or a longer-lasting mulch, such as wood chips or cocoa shells. As with other perennials, cover the bed over the winter with straw and/or evergreen boughs to help protect the bulbs from alternate freeze/thaw cycles.

During the flowering season, remove spent blooms, but try not to cut off more than a third of the stem, which can reduce the plant's vigor and longevity. This can be difficult to follow if you're cutting stems for indoor arrangements. So consider growing some lilies in perennial beds or borders, and others in a designated cutting garden.

Growing Tender Bulbs

Tender bulbs tend to belong to the summer-flowering group and include such popular garden specimens as dahlia, gladiolus, tuberous begonia, canna, and calla lily (Zantedeschia).

Technically, these are not "true bulbs," because they don't contain a tiny flower and stalk inside of them. Instead, the plants grow from bulblike structures known as corms (gladiolus), tubers (dahlia, caladium), and rhizomes (canna). However, they are just as dependable as true bulbs and can be grown in much the same way.

These exotic summer-blooming bulbs can be integrated into the perennial garden, but because they are so popular for arrangements, they're often planted right in the vegetable garden or in a special cutting garden. Plant tender bulbs about the same time as beans and other crops, after the last frost date in spring. Then, around the first fall frosts, when the garden's tender crops are winding down, dig up the bulbs and store them away for the winter.

These tender bulbs vary in hardiness, and it's impossible to give general growing instructions for all of them; different plants have distinct preferences about light, and soil structure and fertility.

Gardeners living in Zone 8 or warmer regions can successfully overwinter cannas, callas, and other types. However, by far the most popular way to grow these exotic tropical and subtropical natives is to dig up the plants around the time of the first fall frosts, allow the bulbs to dry for a short period, and then store them either in paper or mesh bags or placed in a shallow pan or box and covered with dry peat moss. Ideal storage conditions are dry, dark, and cool, around 40 to 50 degrees F.