Okay, now that spring has arrived, you can clean up the garden — sort of.
Wait for warmer weather
According to Savvy Gardening’s Spring garden clean up done RIGHT, we should wait until the daytime temperature warms to a consistent 10°C (or 50°F), so insects that have been overwintering in your garden have had a chance to wake up and leave their winter sheltering spot. The Xerces Society provides additional guidance for figuring out when its safe to start in their article Don’t Spring into Garden Cleanup Too Soon!
Who’s still taking shelter in the garden?
I was surprised to discover that while some butterflies migrate, others overwinter here. The North American Butterfly Association’s Questions and Answers page describes the types of butterflies that do migrate. However, other butterflies and moths overwinter here in one of their life stages, such as in a chrysalis camouflaged on a branch, or as an adult under leaves, bark or rocks. Adult Mourning Cloaks and Question Marks will take shelter in your winter pollinator garden, and emerge early in spring. The drink sap if there are no flowers blooming yet. Then, if the weather cools again, they seek cover to wait some more.
The Wild Pollinator Partners blog post Another good reason to hold back “cleaning up” the garden, describes recent research showing that after queen bumblebees emerge from underground in spring, they hang out in leaf litter as they slowly wake up. If we clean up leaves too soon, we risk raking and bagging queen bumblebees.
Leave the leaves
Continue to leave the leaves on the ground instead of stuffing them into leaf bags; they will decompose to become a free mulch substitute. For a tidier look, remove leaves near garden edges and start a leaf mulch pile elsewhere in your yard. You could also focus on leaving leaves just in shady areas where you’re trying to mimic humus-rich, woodland conditions.
Leave stems 15-inches above ground
Typically, when we clean up our gardens, perennials are cut back to ground level. Instead, cut pithy or hollow plant stems to 15 inches, so they can be used as cavity nests by solitary bees, like Mason Bees and Small Carpenter Bees. Some stems that are used for nests include Joe Pye Weed, Cup Plant, sunflowers, goldenrods, coneflowers, Swamp Milkweed, bee balms, raspberries, elderberries, roses, and sumac. In my garden, I have seen Small Carpenter bees use stems of Anise Hyssop, Ironweed, and Purple Coneflowers.
New plant growth will soon cover the awkward stems that remain.
Chop and drop
I now use the chop-and-drop method to clean up my spring garden. Once I cut off last year’s growth, I chop it up and leave it right in the garden. I used to put it all into leaf bags to be picked up for the city’s composting program. If there’s too much material for my liking, or if the stems are too hard to cut, I simply add them to my own compost pile or brush pile.