Gardening with Native Plants: Early Summer Gardening

Brown-belted bumble bee on cream wild indigo

Brown-belted bumble bee (Bombus griseocollis) on cream wild indigo (Baptisia bracteata)

The June calendar includes the end of spring and beginning of summer. This month, the fully developed tree canopy creates deep shade in the maple basswood garden and lighter shade in the oak hickory and savanna gardens. The prairie gardens and rain gardens have vigorous vegetative growth and early summer forbs and cool season grasses come into bloom. Garden tasks include weeding, edging, and monitoring pollinators. This year, because outdoor work was delayed two months due to the pandemic, we continue trimming and clearing dried material from garden beds.

The native plant garden and Arboretum grounds are open to the public but in-person garden tours and other programs are cancelled this summer (see COVID-19 updates). In place of one of our June tours, here is an overview of the native plant garden.

The native plant garden is located on four acres surrounding the Arboretum Visitor Center. Designed by landscape architect Darrel Morrison, it is a demonstration garden representing native plant communities of southern Wisconsin. Managed and cared for by staff, students, and community volunteers, it is a place for learning and promoting sustainable gardening techniques, plant identification, and pollinator conservation.

The garden includes a variety of woodland, savanna, prairie, and rain gardens. It is home to hundreds of native plant species and animals of these habitats. Staff and volunteers monitor some of these animals, including bluebirds, bumble bees, and monarchs.

Our woodland gardens include the maple-basswood and oak-hickory areas. These areas have spring flowers (ephemerals) blooming on the forest floor in April and May before the trees are fully leafed out. By June, those wildflower seeds are set, and some of the plant species have died back for the year. Others like mayapple (Podophyllum peltatum), wild ginger (Asarum canadense), and bellwort (Uvularia grandiflora) remain green throughout the summer, with leaves held horizontally to capture what little light reaches the forest floor.

Our two savanna gardens differ in soil type and species composition. The black oak savanna is on well-drained sandy loam soil and includes June blooming species like wood mint (Blephilia ciliata) and spiderwort (Tradescantia ohiensis). The canopy trees are Hill’s oaks (Quercus ellipsoidalis) in the black oak group. We have thinned some of the original trees to open this canopy. The bur oak savanna is on medium soil and has taller species in the understory. Species blooming this month include wild geranium (Geranium maculatum), golden Alexanders (Zizia aurea), and yellow pimpernel (Taenidia integerrima). The mature trees are bur oaks (Quercus macrocarpa); shrubs include gray dogwood (Cornus racemosa) and hazelnut (Corylus americana).

Prairie gardens include the sand prairie, lime prairie, dry-mesic, mesic, and wet-mesic prairie gardens. The sand prairie (best seen from the Visitor Center deck) has smaller, more widely spaced plants. Wild lupine (Lupinus perennis), fringed puccoon (Lithospermum incisum), large-flowered penstemon (Penstemon grandiflorum), and June grass (Koeleria macrantha) bloom and set seed this month. The lime prairie (soils are amended with limestone gravel) is also relatively dry. Prairie coreopsis (Coreopsis palmata), harebells (Campanula rotundifolia), and lead-plant (Amorpha canescens) bloom here in June.

The mesic prairie garden represents the tallgrass prairie community on rich soils with medium soil moisture. In June, cream and wild white indigo (Baptisia spp.) come into bloom, along with Canada anemone (Anemone canadensis), ox-eye (Heliopsis helianthoides), and spiderwort.

Two rain gardens are usually managed annually with prescribed fire but were not burned this spring. This may affect the growth of plants as they grow up through the dried material from last year. Species blooming in June include iris (Iris virginica), smooth penstemon (Penstemon digitalis), blue-joint grass (Calamagrostis canadensis), and angelica (Angelica atropurpurea).

May late spring and early summer in our garden inform and inspire you on the longest gardening days of the year.

—Susan Carpenter, native plant gardener

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