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Growing Summer Bloomers in Containers

by Tovah Martin

In New England, as in other cool climates, it's easiest to grow summer-flowering bulbs in containers. Although some summer bulbs claim to be marginally hardy in our neck of the woods, it just doesn't seem wise to tempt fate. Not only are winters cold here, but autumns are unpredictable, creeping in with killing frosts when you least expect a cold snap. Those of us who don't keep our ears permanently tuned to the weather forecast find it easier and less stressful to whisk containers indoors when the temperature drops rather than run out with flashlight and shovel, trying to find stubs that are slipping into dormancy as the thermometer plummets.

Those are the practical reasons why I grow summer-flowering bulbs in containers. From a less objective standpoint, I host my eucomises, dahlias, hymenocallises, acidantheras (renamed Gladiolus callianthus), and callas in containers because they look lovely on my back porch. I put them in pots so that I can shuffle them around at whim. What's more, I can never remember the exact colors of the dahlias, so I move them into color compositions when they open. And even as it unfolds, Dahlia 'Swan's Gold Medal' changes hue daily as its seven-inch-wide blooms unfurl. Part of the fun of gardening is making a moveable feast for the eyes.

Focal Points in Containers

In areas where winters are long and cold and autumns are unpredictable, it's easiest to grow summer-flowering bulbs in containers, making a moveable feast for the eyes that can be rearranged at a whim. [Photo: David Cavagnaro]

I've dabbled in a few summer-flowering bulbs, but my forays are nothing compared with Becky Heath's, whose entire Gloucester, Virginia, garden is devoted primarily to bulbs, experiments in the field. Ask about her favorites for containers, and she'll immediately rush into long and fervent praise of lilies. "They're tall and regal, like models," she says, "but some people complain that they fall over. Ours never fall, and I realized that we've succeeded where others fail because most people don't plant lilies deep enough." For containers Becky recommends burying lily bulbs eight to ten inches below the soil surface. Of course, this requires a container that's deep enough to accomplish the feat. When the bulbs are buried properly, the plants make stem roots that serve as anchors, helping the lilies stand tall, no matter how briskly the breezes blow.

Lilies are Becky's favorite summer-flowering bulbs for the center of a container. Both Oriental and Asiatic lilies give a container height and provide a focal point around which smaller plants can play. The beauty of using lilies as the central figure is that their foliage is handsome before and after blooming. In that capacity, belamcandas, eucomises, crocosmias, cannas, ornithogalums, the taller alliums, and Gladiolus callianthus serve the same function as lilies—all promise blossoms, but they also boast commanding foliage to ride out the season. And all form the top note in a mixed container, although they're equally comfortable growing solo. Hymenocallises also make a certain amount of headway, especially when they're blossoming. However, they tend to send up their fragrant, large, spiderlike white blooms early in the season before your container is really taking off.

Some bulbs are grown for their summer foliage rather than blossoms, and colocasias fit that category. Valued for their immense, elephant-ear-like, heart-shaped leaves in shining green (Colocasia esculenta) or deep purple (C. esculenta 'Black Magic'), they rarely blossom. But who needs blooms when you've got 18-inch-wide leaves? Colocasias need a large container to balance out the leaf span and to act as ballast when the plant is in full glory. But there's no reason why you can't combine Colocasia with smaller, more diminutive bulbs. Colocasia hates to dry out, and the trick is to find a companion that will tolerate the moist conditions that elephant ears require. Caladiums, which also prefer moist conditions and require partial shade, might prove effective partners in a pot, forming a skirt around the colocasia's waist. Hostas, though not summer bulbs, would also tolerate the moisture, as would irises, but I grow my colocasias as a monothematic planter—they certainly hold their own without competition!

Cannas straddle the line between foliage plants and bloomers. Although they slipped from popularity when bedding-plant displays fell from favor, cannas rose again as container plants. With strong, upright stems that send their arrow-shaped leaves pointing straight toward heaven and with colors that range from deep burgundy to red striped with yellow, cannas will get your creative juices going. If all that foliage color isn't enough, cannas crown the affair with large bright yellow, pumpkin-orange, or fire-engine-red blossoms. Some gardeners find the flowers too gaudy for good taste. For those who are inclined toward propriety, a quick snip with the pruning shears will speedily remove the offending flower.

Some summer-blooming bulbs that work well as focal points have too much foliage to make them good bedfellows. Calla lilies and crinums fall into the too-plump-to-share category, and dahlias also seem to work best solo. For excitement, and to accentuate the majesty and colors of these beauties, I use glazed pots or ornamental urns. And I group them side by side with other plants like cupheas, coleuses, and fuchsias that make their colors pop. Dahlias prefer to be planted deep and dislike a very fertile soil. Although they rarely need supplemental watering when planted directly in the ground, they dry out often in a container and require regular soaking to form a continual supply of buds. The Gallery Dahlias—'Art Deco', 'Cezanne', 'Degas', Leonardo', 'Rembrandt', and 'Singer'—were specifically developed for containers, forming compact, well-branched growth that precludes the necessity of staking.

Smaller Bulbs

Becky Heath calls smaller companion plants "shoes and socks plants," because they fill out any container, furnishing a fluff of flowers and foliage around the base of a taller centerpiece. Trailing tuberous begonias can assume the role; achimenes, incarvilleas, and oxalises also work well in that capacity. In fact, all of the above are primarily grown in pots. Both Becky and I agree that they function best and look particularly handsome when framed in a container. To accompany larger containers, you might want to cluster a few smaller pots around them. Kaempferias, caladiums, alstroemerias, eucomises, oxalises, the smaller calla lilies, and achimenes make handsome companion plants.

Potting Bulbs

Be sure to follow planting instructions and install bulbs at the right depth whether you put them in a pot or plant them in the ground. [Photo: Brent and Becky Heath]

The trick to potting any container—whether it holds bulbs or any other type of plant—is to tamp the soil down to fill air pockets. Jar the container a few times while filling it (pick it up and knock it lightly on the ground a few times) to encourage the soil to settle. Moisten the soil before potting to help it firm up in its new home.

Most garden centers sell packaged potting soil specifically formulated for containers. It's easiest to purchase these premixed potting soils, but not all mixes are created equal. Test mixes for suitability by lifting the bag to gauge the weight of the contents. A very lightweight mix probably has a too-generous portion of peat moss and is deficient in loam and compost. Of course, you can always mix in compost purchased separately.

Most bulbs come with planting instructions—follow them, whether you're locating the bulbs in a container or in the ground.

After the Show Is Over

Container-grown bulbs should be overwintered in a cool, dry, dark area. Even if the bulb is hardy in your region, it's not likely to survive outdoors in a container. In fact, if the container is terra-cotta or cement, it should probably move indoors as well; if it is subjected to a cycle of repeated freezing and thawing, it might crack.

Most bulbs can endure a light frost (check the planting recommendations when the bulbs arrive); however, many begin to look tired before the season winds to a close. To coax dormancy along, withhold water, cut back the foliage to the base, shake off the soil, and let the bulbs dry in the sun for a few hours before bringing them indoors. They'll be ready to plant the following spring when frost is no longer a threat in your area. Or, get a jump on the growing season by starting them indoors in April or May.