Sustainable Landcare: Winter Perennials in the Highland Park Entry Garden

As the new year approaches and we anticipate changes in 2021, the observant park user may notice something is slightly different in the Highland Park Entry Garden.

This year, the Pittsburgh Parks Conservancy horticulturalists were credited as 'Sustainable Landcare Professionals,' and are working to implement new sustainable practices at this well-known city garden. Traditional horticultural practices suggest the fall is a good time to cut back your perennial flowers and tidy up before winter; instead, we have chosen to leave the perennial plants in Highland Park standing during the cold winter months. There are many benefits to this sustainable Landcare technique. When left standing, every plant serves multiple unique and vital winter functions that support a variety of species in our urban ecosystems.

For instance, although no longer green and lush, the old foliage of perennial flowers provide shelter for the eggs of beneficial insects and insulate the soil where roots, fungi, invertebrates, and other microorganisms must endure the winter. Many stalks that once held brightly colored flowers remain up right where they are protected from moisture and decomposers in the soil. These dried stalks also provide shelter and habitat for another suite of invertebrate eggs and larvae to survive the long cold months. Several perennial plants reproduce by seeds that remain atop dried flower stalks throughout the winter. Not only does this enhance their fertility by exposing them to the necessary cold temperatures needed for germination (a phenomenon known as “cold stratification”), but those seeds also provide a winter food source for a significant number of permanent and migratory bird species.

Furthermore, not cutting back perennial garden flowers in the fall is a boon to the plants themselves! Many species will maintain green leaves that continue to photosynthesize throughout the winter, thereby strengthening their roots, and supporting healthy soil communities below. When those leaves that do desiccate eventually fall to the ground, they begin to undergo the process of decomposition, ultimately recycling nutrients back into the soil where they can support next year’s growth.

But wait, there’s more! Perennial plants provide a benefit to humans during the winter months too. Many dried perennials offer a stunning aesthetic in the winter as well. Old Hydrangea blooms stand atop their dried stems like lollipops peering over the sleeping gardens. Amsonia foliage and dried Sedum flowers offer a welcome splash of color in the subdued winter landscape. Soft spikes of Liatris and sharp orbs of Echinacea contribute appealing textures while the bare stalks of Asiatic lilies (Lilium) zig-zag towards the sky. Although perennial blooms may be transient, the perennial garden provides an observant viewer year-round interest and delight.

By practicing sustainable Landcare in the parks, we support the Pittsburgh community - humans, plants, and wildlife alike. Towards the end of this winter, we will partner with the city to cut down and shred this perennial biomass in a place where it will serve its final function. Much like traditional mulch, these shredded perennials will restore nutrients and provide a layer of protection and insulation to the garden soil so that new growth can thrive in 2021!

By: Robin Eng, Restoration Gardener, Pittsburgh Parks Conservancy