April brings many transitions in the garden: temperatures rising, days lengthening, buds breaking, animals and insects emerging, seeds germinating, and more gardening. The land comes to life. At the Arboretum, our long-term phenology records include 43 April events; 70 percent of those events are records of “first flowering.” About half of these records note bloom times for our largest plants – trees and shrubs – with relatively tiny flowers. The other records make note of herbaceous early spring blooming species in woodlands and prairies.

Trees and shrubs blooming this month hold flowers in catkins or clusters, or they have conspicuous petals.  Some species bloom before their leaves have expanded. Many species are wind-pollinated, at least in part. Copious amounts of pollen are produced in wind-pollinated species, and evolution favors plant with forms that allow pollen to travel without obstruction and land on a female flower to later produce fruit. (Unfortunately, these generous amounts of pollen may cause spring seasonal allergies, too.) Some early blooming trees and shrubs are also pollinated by early emerging bumble bee queens, mining bees, cellophane bees, and flies.

Some of these April blooming species are “dioecious,” meaning they mostly have male and female flowers on separate plants. Examples include box elder (Acer negundo) and red maple (Acer rubrum), which bear their flowers in pendulous clusters. These trees’ wind-dispersed seeds are carried in winged fruits. Red maple seeds can germinate early in the summer. Another dioecious species, red cedar (Juniperus virginiana) releases pollen from the small pollen cones on one tree to the seed cones on another. Its seeds are dispersed by birds and other animals. Pussy willow (Salix discolor) is a dioecious shrub; the familiar soft buds are the male catkins before they bloom. Other species such as trembling aspen (Populus tremuloides) and Eastern cottonwood (Populus deltoides) are “monecious,” with separate male and female flowers on the same plant. The flowers bloom on narrow catkins and mature seeds are wind-dispersed on cottony hairs. American hazelnut (Corylus americana) is a monecious shrub, with long male catkins and clustered female flowers with short purple styles.

Late in the month, Juneberry (Amelanchier spp.) and American Plum (Prunus americana) come into bloom as the leaf canopy is starting to develop. These two species have “perfect” flowers with conspicuous petals. Stamens and styles are produced within the same flower. Insects visit these flowers to pollinate them, and birds and other animals disperse the seeds that develop in fleshy fruit.

At ground level, April brings many wildflower blooms in savanna and wooded sites. Some of these species are true ephemerals, for example, Dutchman’s breeches (Dicentra cucullaria), toothwort (Cardamine concatenata) and spring beauty (Claytonia virginica). Others, including bellwort (Uvularia grandiflora), bishop’s cap (Mitella diphylla), and bloodroot (Sanguinaria canadensis), maintain their leaves into the summer months. In open sites, April flowers include pasqueflower (Anemone patens), and prairie-smoke (Geum triflorum). April weeds include garlic mustard (Alliaria petiolata), yellow-rocket (Barbarea vulgaris), and creeping Charlie (Glechoma hederacea).

While these wildflowers bloom, you may observe solitary bees and new bumble bee queens foraging or searching for nest sites. Resources for monitoring and identifying the latter are at Bumble Bee Brigade.

As we part leaves to find small spring flowers emerging in our gardens, let’s not miss the spring pollinators flying and buds flowering overhead.

—Susan Carpenter, native plant garden curator