The mowing down of the garden in spring used to be straightforward – a crew would ride mulching mowers around the garden to make a clean palette for the anticipated crocus and tulips. While Lurie Garden’s first priority is maintaining the garden’s design beauty and accessibility for visitors, it also strives to increase its ecological benefit.

Laura passes out maps to the cut-back crew indicating which areas should be mowed completely.

In early 2018, Laura Ekasetya, the garden’s former Director and Head Horticulturalist, embarked on a new experiment to be more helpful to native bees and other bugs, especially in light of insect populations plummeting, by not cutting parts of the garden all the way to the ground.

In 2018 designated areas for reduced cutting were flagged to give the crew a visual guideline as to where to stop mowing.

During the growing season, many insects use standing spent plant stems as nesting sites, particularly the bottom 15-inches of the stem. According to insect expert, Heather Holm, “Cavity nesting insects which include most cavity-nesting bees and some solitary wasps use the hollow stems…A few bee species, including small carpenter bees and mason bees, construct their nests in pith-filled plant stems, chewing the pithy material from the center of the stem to create a nesting cavity.”

“A small carpenter bee enters a nest in a plant stem.” – Image and caption by Heather Holm.

An array of tulips wouldn’t be as instagrammable mixed in with a bunch of twigs sticking up from the ground, so it was decided to experiment slowly while leveraging the strengths of each area of the garden. Laura surveyed the overall design plan and chose areas that are a little less picturesque in the very early spring to leave 15-inch stems standing and areas where tulips and crocus bloom en masse were cut down completely as previously done. By mid-spring, the standing stalks were camouflaged by the grown plants and looked as it always has.

Areas that are mowed down completely are areas where a clean pallet is essential for the garden’s design features.

Even though most of the garden continues to be cut back completely, it still offers plenty of ecological value. As the mowers pass, the plant material is coarsely chopped to stem pieces that are 3-12″ long and left on the ground which acts as a natural mulch. This mulch keeps moisture in the soil, provides nesting materials for birds and insects, and fertilizes as it decomposes.

As the mulching mowers pass, the plant material is coarsely chopped and left on the ground which acts as a natural mulch. While some overwintering insect’s habitat could be damaged in this process it is the least damage we can manage and still balance efficiency and aesthetics. 

For 2019 the mowing plan included an expansion of the areas reserved for insect habitat. As the season proceeds, the staff will assess how the respective areas fill out, to see how the mowing/insect nesting areas for the next winter could be adjusted to add the greatest value.

The areas reserved for insect nesting habitat more than doubled between 2018 and 2019. The areas will be assessed during the year and be adjusted if needed for the following year.

We may end up not knowing how many insects take advantage of the stems left up for them, and that is ok. As visitors, maybe some who may care for other gardens, come through the garden they may notice this unusual ‘gardening’ technique, learn about its benefits, and cause them to not cut back their gardens as severely as they used to.

According to Heather Holm insects like plants with “long, linear, strong flower stalks.” In her book, Bees: An Identification and Native Plant Forage Guide she lists asters, goldenrods, thistles, bergamot, black-eyed Susans, and coneflowers as some plants they may favor for their nesting.

Signs are posted around the garden to inform visitors as to why stems were left standing, hopefully inspiring other gardeners to refrain from cutting back their gardens completely too.

Meanwhile, the Lurie Garden staff will be on the lookout for nesting insects this growing season. They will look for pith particles coming out of the tops of some of those stems or small fresh shavings on the ground around stems as evidence that keeping this nesting area is really paying off!

This is what success looks like! As insects burrow into a stem, pith can be left at the entryway to their new nest! These insects will emerge from these stems the following spring. Photo by Heather Holm.

Here is a great visual guide for this process.

Let us know if you find any nesting insects and what you think about our experiment, especially as the spring progresses!

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