Gardening with Native Plants: Summer Shift

Rusty-patched bumble bee

Rusty-patched bumble bee (Photo: Kymberly C.)

August brings mostly warm days, and perhaps subtle cooler hints of fall. It can be a rainy month, or a time when dry conditions deepen. Garden colors begin to shift to fall hues. Early August marks the halfway point of the average growing season, as measured between the last 32-degree-Farenheit day in the spring and the first 32-degree-Farenheit day in the fall. One hundred and sixty days is the average length of the growing season for the Madison area. Garden tasks include weeding, managing aggressive native species, trimming along paths, seed collecting, preparing for our annual Native Gardening Conference, and monitoring bumble bees.

Our new garden area, the dry prairie, was established one year ago with more than a thousand plants. We added several hundred more plants in 2022. So far, five native short grasses are planted in curved zones, and forbs are placed in drifts. June grass (Koeleria macrantha), a cool season grass, already bloomed and is setting seed. Side-oats grama (Bouteloua curitipendula) and northern prairie dropseed (Sporobolus heterolepis) began blooming in July, and purple love grass (Eragrostis spectabilis) and little bluestem (Schizochyrium scoparium) will come into flower this month. Forbs in bloom early this month include: mountain mint (Pycnanthemum virginianum), purple prairie clover (Dalea purpurea), and rough blazing-star (Liatris aspera). Old-field goldenrod (Solidago nemoralis) will flower later in August. The weeds we observed (and pulled) last year are still a factor, but there are fewer pokeweed and crabgrass seedlings, at least so far. One benefit of keeping up with weeding in this young garden is that we’ve noticed several native solitary bee species digging areas of bare soil to create narrow underground chambers for their egg-laying and provisioning.

Brown-belted bumble bee
Brown-belted bumble bee (Photo: Emma T.)

When monitoring bumble bees in the gardens this season, we typically find six to seven species, including the endangered rusty-patched bumble bee (Bombus affinis). For most of July we saw only female workers (gathering pollen for the larvae growing colony). But recently, we also observed some male bees and large newly hatched future queens, especially of species like two-spotted bumble bee (Bombus bimaculatus) that typically emerge early in the spring. During this month, most bumble bee colonies transition from growing the number of female workers to producing bees that mate – males and future queens. Females continue to forage this month for the developing larvae in the nest.

I am offering a free bumble bee workshop on Saturday morning, August 13, from 9 a.m. to 12 p.m. This session will include an overview of Wisconsin bees, bumble bee biology, life cycle, photography, basic ID, and submitting your findings to Bumble Bee Brigade. We will spend time in the field looking for bees and practicing photography, weather permitting. If you are interested in monitoring bumble bees in your garden or places you visit, please register by emailing me by August 10. Space is limited.

Savor late summer in your garden and at the Arboretum!

—Susan Carpenter, native plant garden curator