Early spring gardening: A call to preserve pollinator habitats amidst seasonal clean-up
Colorado State University Extension
The first crocuses are emerging, grape hyacinths that haven’t been demolished by the bunnies are nearly flowering, and I spotted a ladybug crawling through the mulch around my roses this weekend. The recent warm weather has definitely brought on the gardening itch. So, is it time to start cutting back last year’s plant stalks and cleaning up the other debris that accumulated this winter? For the sake of our pollinators and other beneficial insects, maybe not.
The recent Colorado Native Pollinating Insect Health Study notes that the first step to pollinator conservation is protecting existing pollinator habitat, including food resources, reproduction sites, and nesting and overwintering sites – like last year’s plant debris. Queen bumblebees, some butterfly and moth larvae – like the white-lined sphinx moth – and other arthropods overwinter in debris left on the ground.
This isn’t the only place you’ll find overwintering insects. Of Colorado’s native bee species, approximately 30 percent are cavity nesting. Important nesting sites include plant stalks with spongey piths. This includes annuals like sunflowers and the stalks of many perennial plants, like roses and raspberries. Insectfriendly
Leaving areas of bare, sunny ground provides important nesting and overwintering habitat for insects.avoiding these areas until insects have begun to emerge is also important.
cavities may also include holes in trees left by other wood boring insects, and crevices in house siding and wood fences. If you are going to cut plants back early, stick the stalks in the ground in a protected location so insects can emerge when the time is right.
More importantly, of Colorado’s more than 1,000 native bee species, approximately 70 percent are ground nesting, meaning they overwinter in the soil. This means many of our overwintering pollinators are
one careless step away from catastrophe. It’s important to be mindful of where you walk lest a stray garden clog spell disaster for an overwintering insect. Overwintering insects are vulnerable, both because they often overwinter in a juvenile stage (e.g., larvae), and because they are exothermic (they cannot regulate their own body temperature, like humans) and cannot be active until temperatures have warmed enough to support movement, usually when temperatures are reliably around 50 degrees
Fahrenheit.
Leaving areas of bare, sunny ground provides important nesting and overwintering habitat for insects. Avoiding these areas until insects have begun to emerge is also important.
There are other reasons to avoid working the soil until the weather is warmer and drier. Soil structure is fragile and working the soil using practices like digging or tilling too early in the spring risks destroying soil peds, or aggregates, that create a soil’s pore space along with overwintering insects. Healthy soil is composed of approximately 45 percent mineral content (the “dirt” of soil), five percent organic matter, approximately 25 percent water and 25 percent air. These last two – air and water – are contained in the pore space in uncompacted soil.
Rather than scratch that gardening itch by cleaning up last year’s debris, I left the insects to their rest, and decided to spend a few hours simply sitting in the sun with a good seed catalog, leaving cleanup for another day.
Micaela Truslove is a Commercial Horticulture Specialist at Colorado State University Extension. For more information, visit extension. colostate.edu or call 303.678.6286