Eastern Redbud: Early Flowers Mark the Beginning of Spring
By T'ai Roulston, Curator
The eastern redbud (Cercis canadensis) is well loved, commonly planted, and native to most of the eastern United States. It has few detractors, mainly contrarians that denigrate anything common and literalists who find the buds and flowers not sufficiently red to earn the name. Aside from these minor blemishes, it is a plant to behold, propagate and appreciate, from both an aesthetic and an ecological viewpoint.
As a wild plant, it is home in open woodlands, especially the edge where forest yields to field or roadside, lots of light but not too dry. As a small tree, it goes unnoticed until just before bloom, when the rose-pink flowers burst from clustered buds along the stems. Their sprays of color stand out even more when the backdrop is leafless trunks of oaks and maples, a wispy pink before a wall of gray. As much as we appreciate it, we are not their biggest fans. The eastern redbud is a key floral resource for many of our bees.
When the redbud blooms, in March or April depending on the spring, bumble bee queens have just emerged from a hole they dug last fall and seek to start a colony. At first, they feed themselves on nectar and pollen and then they search the ground for an abandoned mouse nest or some other hidden cavity to rear their young. When that is found, they collect nectar and pollen to feed their first workers, which they alone must rear for several weeks. It is a dangerous time to be a bumble bee queen. They must leave their nest to forage, leaving no protection for their developing offspring. They themselves are large and plump, a tempting morsel for a hungry bird, so each time they leave the nest they risk their own life and that of their offspring. So at that time of year, finding plants with lots of flowers rich with pollen and nectar is key: the more flowers in the landscape, the less time they and their offspring are exposed.
Redbud is a great plant for them to find. All of the six common bumble bee species at Blandy forage on redbud. In the woodland section of the Native Plant Trail, they link the redbuds with their flight, moving tree to tree like hikers who hop on stones to cross a river. Whole trees are full of them, their legs swelling with pollen as flower petals fall below. In our area it may be the most important tree for bumble bees, ensuring success for the colonies that will later converge on milkweed, bee balm and our garden vegetables. Many other bee species use it too. The blue orchard bee, a native species that helps pollinate our fruit trees, has been shown to collect mostly redbud pollen in Virginia before the orchards bloom. A study that examined how many warm days in spring it takes the blue orchard bee to emerge from its nest concluded that it seems to use the same temperature cues used by redbuds to flower, thus always emerging at a good time to find redbud in bloom. When you see the redbuds this year look to see who found it first.
The eastern redbud is widespread in the eastern United States. It hits all states outside New England (I too, no longer tolerate that cold). To the west, it skips the northern prairie and peters out in the face of the western deserts. A couple of varieties, C. canadensis texensis and C. canadensis mexicana, push the species into Texas but that's about as dry and hot as it wants to go. The western species (California redbud or western redbud) continues the redbud line all the way to the west coast, so almost all of the continental United States has a redbud species the locals can champion.
As a horticultural tree, it is easy to grow. It can take full sun or substantial shade, tolerate soils from alkaline to acidic, and is tolerant of pollutants like ozone, which has helped boost its recent popularity as a street tree. It grows quickly and lives a decent life, 50-75 years. It is not without disease, fungal canker being among the worst, but it still tends to live quite a while even when infected. Old redbuds often grow flowers directly from their trunks, something called cauliflory, a common trait in tropical trees but rare in temperate. Several of the older ones in the Native Plant Trail do this, but it's not known why it happens. Like people, even old trees can grow things in unusual places.
As easy as it is to grow, it still has some enemies in the wild. One of our most serious invasive plants in our forests is the Amur honeysuckle, which often forms dense thickets in the understory where redbud tends to grow. Not only will the honeysuckle steal the light, it also puts allelochemicals into the soil that inhibit the growth of other plants, redbud especially.
Some may know the redbud as the Judas tree. The very similar European redbud, Cercis siliquastrum, is called the Judas tree because Judas Iscariot was said to have hanged himself on the tree after betraying Christ, causing the pure white flowers to become tinged with blood. If you prefer less shame and sacrifice in your selection of ornamental trees, pre-betrayal colors ('Alba') are available in both the European and the American species. Either way, it is an important tree of the forest that also enlivens the yard in spring.