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Our Backyard Gardens: Spring Pruning for Pollinators

By Amy Halsted

The olde rudbeckia stems provide excellent nesting sites for bees. Photo by Amy Halsted

To meet the needs of butterflies, moths, hummingbirds, wasps, flies, long-tongued and short-tongued bees, pollinator habitat plants in the backyard garden should be pruned in the spring. Pollinator plants should feature a variety of natives, bulbs, perennials, grasses, shrubs, trees, fruit trees, wildflowers, and annuals. 

Plant diversity creates opportunities, particularly for nesters. While many bees build ground nests, numerous bee species - leaf cutting, yellow-faced, mason, resin, carpenter, and more - nest in hollow, pithy, and dead stems. Raspberries, grape vines, sedums, lupines, asters, Joe Pye weeds, echinaceas, stonecrops, bee balms, rudbeckias, to name but a few, provide excellent nesting sites. 

Pollinators emerge from overwintering nests at various times during the spring, depending on the weather. This is also the starting point of their “developmental” year. In the case of bees, emergence includes collecting pollen and looking for future nesting sites. They pack pollen and nectar into stems to lay eggs using chambers divided by mud or plant material. Larvae hatch, develop through the year, hibernate during the winter, and emerge the following spring. Spring pruning takes into account that some pollinators are still hibernating while some are looking for yearlong nests. 

With pruners in hand, only a few patches of snow on the ground and daytime temperatures nudging fifty degrees, cut everything back. To create vertical nesting, leave plant stems between eight and twenty-four inches while recognizing that plant diversity (and relative stem width) supports a variety of pollinators’ body sizes which is generally range from one-tenth inch to one inch. Taller, wider plants are pruned to twenty-four inches while shorter, narrower plants will be eight inches. If in doubt, fifteen inches is a good height.

Butterflies and moths lay their eggs on plants, trees, and shrubs - particularly native species - which provide food and shelter for caterpillars. Spring blooming shrubs - forsythia, lilac, weigela, rhododendron, azalea, dogwood - are best pruned right after blooming. Leave four to six inches from a branch or stem node. Plants with pith-filled or hollow centers are prioritized for nests. Compost or bundle together the tops of plants to create additional nesting sites. By early summer, new plant growth will cover pruned stems that remain.

Emerging pollinator populations make for an exciting time in the garden. Watch pruned nesting sites to see insects exploring future nests while remembering that some of last year’s stalks may yet house overwintering adults, larvae, and pupae. Leaving stems during the growing season ensures larvae develop in the summer garden.

Pruning for pollinators is also an opportunity to inspire fellow gardeners and neighbors to create sustainable landscapes by leaving the backyard garden untended in the “usual” way. Installing a “Habitat” or “Pollinator Garden” sign broadcasts barren stems as potential homes for pollinating insects which carry pollen to the plants which depend on it for fertilization. By avoiding too much fall clean up, we can allow seed heads and stems to provide food and shelter for pollinators in the winter garden, while creating visual interest throughout the winter months. Leave pruning for the spring in order to nurture the yearlong pollinator development cycle.


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