April brings welcome spring to southern Wisconsin. In deciduous woodlands, small spring ephemerals emerge and flower, and tree canopy leaf-out begins. In prairies and savannas, several species bloom as green-up begins, especially on sites that have seen dormant season prescribed fire. It seems that every shade of green appears on the landscape this month. Bird song intensifies and nesting is underway for some species. Garden tasks include trimming, edging, looking for signs of spring, and avoiding areas too muddy to work. After a two year break due to the pandemic, volunteers will return to the Native Plant Garden this month, weather permitting.
With warmer April temperatures, dormancy breaks in the insect world as well. During the winter we planned gardens and plantings to support pollinators; this month we see some pollinators emerge to forage and reproduce. Some solitary bee species complete their life cycle for the year within a few short weeks in the spring. Found visiting early blooming willow, leatherwood, ephemerals, and non-native bulbs, ground-nesting bees come out from underground chambers and mate. The female bees begin populating new nest chambers with pollen provisions and one egg per chamber, laying a few dozen eggs that will develop over the next year.
In southern Wisconsin, April 15 is the average date for bumble bees to emerge from winter dormancy. These large bees mated last fall before overwintering. They must find a place to start their nest – usually underground or hidden above ground, as in compost or under plant material. They also must find adequate nectar and pollen to feed themselves and provision dozens of eggs, which will become the female workers in the first month of the colony. Those workers will then forage to support and continue building the annual colony of several hundred bees throughout the rest of the season. A healthy colony will produce multiple future queens and males later in the summer and early fall.
Early spring resources include flowering trees like plum and cherry (Prunus spp.) and Juneberry (Amelanchier spp.). Herbaceous plants like wood betony (Pedicularis canadensis), shooting star (Primula meadia), prairie smoke (Geum triflorum), and spring ephemerals are also used. Native plants are ideal for native bees, but non-native sources of nectar and pollen can help support them, too. Additional resources are provided by non-native spring bulbs like squill (Scilla spp.) and weedy mints like creeping Charlie (Gleochoma hederacea) and dead nettle (Lamium spp.), often found in untreated lawns.
The Arboretum is working with the UW–Madison Office of Sustainability to demonstrate and teach about the biological and ecological value of lawns that include flowering species. Instead of maintaining a turfgrass monoculture, the Arboretum has untreated lawns that include dandelions, red and white clovers, plantains, creeping Charlie, dead nettle, self-heal, and more. While none of these are native plants, they do provide resources and are used by many species. These lawns are managed without fertilizer, irrigation, or herbicides, reducing cost and providing healthier habitat.
For more information on pollinator-friendly lawns, see this Planting for Pollinators gardening resource from Minnesota state agencies and the Xerces Society.
Enjoy April in your garden and at the Arboretum!
—Susan Carpenter, native plant garden curator