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Be a Better Gardener: A second season for bulbs

Tiger lilies (Lilium lancifolium) are winter hardy to USDA zone 3 and put on a good show in summer gardens.
May 13, 2019 11:39 am Updated: May 13, 2019 11:42 am


Most of the gardeners I know don’t think about bulb planting until the fall. By doing so, however, they miss another, extra season of bulb beauty. Summertime brings its own selection of bulbs to the garden, and the planting time for these mid-season delights is right now.

Summer bulbs offer many of the same advantage as the fall-planted, spring-blooming bulbs. That is, they practically guarantee flowering and spectacular blossoms. What’s more, the summer bulbs, like their spring brethren, provide flowers for the garden at a time when little else is on show, for the summer bulbs bloom right through the dog days when other flowers flag. Nor are summer bulbs particular about soil; some will even thrive in damp soils that would cause most spring-blooming bulbs to rot.

One limitation of the summer-blooming bulbs is that most of them are not winter hardy in our region. This means you can treat them like annuals, replanting every year, or you can dig them up when the first frost threatens in fall and store their roots in boxes of sphagnum peat over the winter, then replant them the following spring.

One class of summer bulbs that offers many representatives winter hardy in our region is the true lilies. Tiger lilies (Lilium lancifolium), for example, are winter hardy to USDA zone 3. They used to provide quite a show in my front garden, self-seeding and proliferating, until they were cut down by an imported pest, the red lily leaf beetle, a few years ago. The recommended organic control is applications of neem oil at five to seven-day intervals, combined with handpicking of the adult beetles, but I wasn’t able to keep up with the spraying schedule.

To plant summer-flowering bulbs, wait until all danger of frost is past. Dig in a good dose of compost — virtually all of the summer-flowering bulbs like an organic-rich soil. Most prefer a well-drained soil, but cannas and elephant ears (Colocasia esculenta) also thrive in soils that stay consistently moist or even wet; I’ve seen both flourishing in pots set in the shallow parts of garden pools.

For summer-bloomers that make true bulbs, such as lilies, or corms, like gladioli and elephant ears, treat them as you would the more familiar fall-planted bulbs. Plant them three times as deep as the bulb is high, and make sure the buds or growing points are facing upwards. The kinds with tuberous or rhizomatous roots, such as dahlias or cannas, should be planted with the roots horizontal and any ‘eyes’ or buds facing upwards. Plant dahlia tubers 2 to 4 inches deep and canna rhizomes 4 to 6 inches deep.

Most summer-flowering bulbs prefer a sunny location. Some, in particular the large-leaved, tropical kinds such as cannas, elephant ears, caladiums and calla lilies, will grow well in partial shade but may not bloom in those conditions. You may not care; their flamboyant leaves add a lot to a shady border, providing a bold counterpoint to more delicate but colorful coleus and impatiens. These tropical bulbs, incidentally, are fast-growing and greedy feeders, so they benefit from monthly applications of some balanced organic fertilizer. Avoid high nitrogen fertilizers — the nitrogen content is represented by the first number in the three-number formula on the fertilizer label. Excessive nitrogen promotes leaf growth at the expense of the flowers and the roots.

Dahlias used to be a source of disagreements in my household, with my wife Suzanne as an enthusiastic admirer and me disdaining them as gaudy and obvious. I have since come around to agree with Suzanne. I am especially enamored of the kinds with dark foliage to set off the vivid flowers. A classic of this sort is ‘Bishop of Llandaff’ whose dark purple, almost black, leaves make an elegant setting for the fiery red peony-type blossoms. I’m still not entirely comfortable with the so-called ‘dinnerplate’ dahlias, whose outsized, 12 to 14-inch blossoms perch atop stems 3 to 4 feet high. They have an in-your-face quality that turns me off, but that may be just because I’ve never seen them used imaginatively. To produce the biggest blooms, the dinnerplate dahlias also require special treatment. They must be supported by stout stakes and the side shoots pinched off the main stem to encourage the plant to put all of its energy into the central blossom. If you don’t mind this extra fussing, the reward will be the biggest blossoms in the garden.

Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, located in Stockbridge, Mass. Its mission to provide knowledge of gardening and the environment through 25 display gardens and a diverse range of classes informs and inspires thousands of students and visitors on horticultural topics every year. Thomas Christopher is the co-author of Garden Revolution and is a volunteer at Berkshire Botanical Garden.