Q:
Why do the bleeding hearts in my garden go dormant in summer, when so many other perennials are bright green or in flower?
Bob Connolly, Hartford, CT
Bleeding hearts go dormant in summer. To extend the growing season of ephemeral wildflowers, water regularly, fertilize lightly, and apply compost in spring.
Photo/Illustration: Jennifer Blume
A:
Horticulturist Charles W. G. Smith replies: Bleeding hearts (Dicentra spectabilis) are included in a group of spring-blooming perennials called ephemeral wildflowers. These diverse plants, including spring beauty (Claytonia virginica), hepaticas (Hepatica spp.), and trilliums (Trillium spp.), thrive in deciduous woodlands. The special growing requirements of ephemeral wildflowers combined with specific environmental stresses cause many of these plants to enter dormancy at a time most of us regard as the height of the growing season.
Stated most simply, growth and dormancy are opposites that are driven by changes in environmental conditions. The most important environmental factors affecting growth and dormancy are light intensity and duration, moisture, and temperature. Early spring provides optimal conditions for the rapid growth of ephemeral wildflowers. Sunlight is intense through leafless trees, the nights are short, moisture levels are excellent, and temperatures are moderate. At this time, many perennials, shrubs, and trees are just breaking dormancy, while ephemeral wildflowers are at maximum growth. As the season progresses, emerging tree leaves reduce light intensity. After the summer solstice, the nights begin to lengthen. Rain is less frequent and temperatures climb to levels that inhibit photosynthesis. These factors initiate dormancy in many ephemeral wildflowers, often as soon as early summer.
The changes within the plant are initiated by changes in levels of specific hormones. When conditions for growth are optimal, the hormones that are associated with growth, such as auxins, are high, while levels of hormones regulating dormancy, such as abscisic acid, are low. When optimal conditions for growth change, the balance is reversed.
Though bleeding hearts and other ephemeral wildflowers are frequently dormant by midsummer, these plants can be kept green and attractive for a few weeks more with a little special care. To delay initiation of dormancy in ephemeral wildflowers, follow these simple guidelines: Water regularly throughout the growing season, apply a water-soluble fertilizer at one-quarter strength every two weeks, and apply a 1-inch-deep layer of compost mulch in spring and refresh as needed.
