April can be a month of all-too-rapid spring growth or all-too-slow development in our gardens and landscapes. Often, the month brings both as temperatures and precipitation vary widely. With warmer than average weather in February and March this year, some species in the native plant garden bloomed last month: wind-pollinated Eastern red cedar (Juniperus virginiana), American hazelnut (Corylus americana), and pasqueflower (Anemone patens), which is pollinated by small bees. Prairie-smoke (Geum triflorum) and shooting star (Dodecatheon meadii) rosettes (short stalks with many leaves close to the ground) have emerged, but the flowering stalks have not extended yet. When blooming, these two species do not produce nectar, but they are a pollen source for (and are buzz-pollinated by) bumble bee queens, and possibly by smaller bees who gather pollen to provision their eggs.

In woodlands and shaded gardens, spring ephemerals begin their weeks-long life cycle, including emergence, growth, flowering, seed set, and senescence, as the tree canopy fills with leaves. Plants emerging on the sunny forest floor may show red pigments before the photosynthetic system is fully active and the plants green up. Flowers may be held in within rolled leaves as they come through the leaf layer, or stalks may emerge first to break soil and uncurl as the stem lengthens toward light.

These small plants of the forest floor are very important for early pollinators. Bumble bee queens visit ephemerals for nectar and pollen during the crucial time they are establishing nests and raising the first group of female workers within the colony. Plants like Dutchman’s breeches (Dicentra cucullaria), Virginia bluebells (Mertensia virginiana), Jacob’s ladder (Polemonium reptans), wild geranium (Geranium maculatum) and woodland phlox (Phlox divaricata) are valuable nectar sources for large and small bees, butterflies, day-flying moths, bee flies, and wasps. Some of these plants host a specialist bee species that collects only its pollen to provision eggs. While there are published observations of plant-and-insect relationships for some native plants, your own observations could add to this knowledge. Photography and identification aids could allow you to explore this sometimes-hidden world in your own garden.

This will be our fourteenth season of monitoring bumble bees at the Arboretum. We began frequent photo surveys after a visitor from California in 2011 shared his photo of a rusty-patched bumble bee in the native plant garden. Fast forward to 2024, the Wisconsin Department of Natural Resources project Bumble Bee Brigade provides resources and training for bee photography, bumble bee identification, and submitting your photos. The project also shares hundreds of observations from throughout the state. Learn even more by participating in the Wisconsin Bumble Bee Observers Facebook group. We will offer two in-person workshops at the Arboretum in July and August during the bumble bee season – contact Susan Carpenter for more information or to register.

Garden tasks this month include trimming or moving aside last year’s dried plant material to allow emerging plants more sunlight, prescribed fire in several areas to stimulate growth of prairie and savanna species, and photo surveys to document the early spring bees and the plants they are visiting. As spring weather settles in, we’ll welcome new and returning native plant garden volunteers!

Enjoy April, in all its variability and promise for the growing season ahead.

—Susan Carpenter, native plant garden curator