Spring bulbs in the Water-Smart Garden

Guest column by Dan Johnson
Posted 4/29/21

Some plants just like it dry — thriving in that spot that you thought was hopeless precisely because it has lean soil and never stays wet for long. Or, the plant may prefer a “wetter” season …

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Spring bulbs in the Water-Smart Garden

Posted

Some plants just like it dry — thriving in that spot that you thought was hopeless precisely because it has lean soil and never stays wet for long.

Or, the plant may prefer a “wetter” season followed by a drier dormant season. This is where lots of our best bulbs come in, hailing from the cold dry steppes of Eastern Europe and Central Asia, or the mountains and steppe of South Africa.

Denver Botanic Gardens’ Water-Smart Garden is nearly overtaken with flowering bulbs in the spring. Those that thrive here have a few things in common: They take advantage of abundant seasonal moisture, exploding into growth with leaves and flowers during our wettest season (April-early June). Then their foliage dries out and disappears, returning to a dormant condition as our season gets warmer and drier. They all tolerate long periods of cold, dry conditions.

Bulbs that get our earliest attention are the first to appear after a long winter. This includes smaller Iris reticulata, Muscari (grape Hyacinth) and the dozens of species tulips and crocus — these are the original forms that most hybrids were developed from. All of these are especially durable and resilient for many years in the right conditions, getting us through that last bit of wintry weather with a ray of hope.

When the smaller-species tulips begin to bloom, it’s easy to appreciate their jewel-like colors, and easy to understand how a “tulip craze” started centuries ago and still continues today.

The real showstoppers soon follow — ornamental onions, Allium and the foxtail lilies called Eremurus. These are native to open grasslands and mountain meadows from Europe to the Himalayas. The foxtails come in shades of pink and white, through yellow and orange, producing enormous spires of color from three-to-eight feet tall, above strappy leaves that soon disappear after flowering. Alliums are stunning with globes of flowers from white through many shades of purple and violet. Several species of allium are also native to arid portions of Colorado and the West, though most have smaller flowers.

Though not true bulbs — technically fleshy rhizomes — bearded iris are a staple in cold-climate gardens and they thrive in Colorado. While used easily in most traditional gardens, they are superbly adapted to drier gardens as well. The Water-Smart Garden features roughly a half dozen true bearded iris, but you will also see some of the more exotic looking specimens scattered through the plantings. These are called arilbred iris — complex hybrids between bearded iris and several wild species from dry regions of the Middle East. Not commonly grown, but well worth seeking out, they prefer drier summer conditions than the standard bearded iris. Their hallmark is often a goblet shape with ornate veining or brush marks on the petals, giving an exotic look.

Watering all these bulbs is hardly a concern. The Water-Smart Garden is rarely irrigated before May, and then is watered only between six and 10 times through the growing season. This varies, depending on precipitation, but the garden is always allowed to become quite dry between watering.

Keep in mind that the bulbs are just one layer in a diverse garden. This theme is echoed in the Steppe Garden, Plant Select Garden and parts of the Rock Alpine Garden. Visit us at the Denver Botanic Gardens often to see what each changing season brings.

Dan Johnson is the associate director of horticulture and curator of native plants for the Denver Botanic Gardens

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