Cutting Back on the Cut-Back

Traditionally, in late winter, mulching mowers have rolled into Lurie Garden to cut down all the previous year’s growth. While Lurie Garden’s first priority is to maintain the garden’s design, we also strive to increase its ecological value. Could the cut-back be more ecologically friendly?

In early 2018, the garden’s Director and Head Horticulturalist, Laura Ekasetya, embarked on a new experiment: In order to support plummeting populations of native bees and other bugs, parts of the garden would not be mowed.

During the growing season, many insects use certain standing plant stems as nesting sites, particularly the bottom 15 inches of the stem. According to insect expert, Heather Holm, “Cavity-nesting insects, which include some bees and solitary wasps, use standing plant stems to construct their nests. They chew the pithy material from the center of the stem to create a nesting cavity.” But clusters of delicate tulips intermixed with standing twigs wouldn’t be very Instagrammable, so it was decided to experiment slowly to see which areas could be left standing while not interrupting the design.

Laura surveyed the design plan. The garden’s design favors certain areas in the early spring. Places where tulips and crocus are meant to shine would be cut down completely as before. Areas less picturesque early in the year would be cut back to 15 inches. By mid-spring, the standing stalks would be camouflaged by the grown plants and look as they always have.

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 into pieces that are 3-12″ long and left behind. This layer of material acts as a natural mulch that keeps moisture in the soil, provides nesting materials for birds and insects, and fertilizes as it decomposes.

For 2019, the mowing plan included the expansion of areas reserved for insect habitat. As the seasons proceed, the staff will assess how everything fills out. Adjustments to the areas left standing will be made to offer the greatest value while not disturbing the intended design.

We may never know how many insects take advantage of the stems left for them, and that’s ok! As visitors come through the garden they may notice this unusual ‘gardening’ technique, learn about its benefits, and be inspired to be less severe with their loppers. If you hope to create a nesting habitat like this in your garden, Heather Holm says insects like “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.

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

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