In summer, the native plant gardens at the UW Arboretum sequester carbon while adding beauty and habitat. Designed by Darrel Morrison.

 

Gardeners new to the concept of carbon gardening often ask these two questions: What good soil management strategies will help maximize carbon sequestration? And, what would be a good plant palette to help accomplish this? Good questions both, to which I wish I could give detailed, specific answers. Carbon gardening in northern Illinois, where I live, differs from carbon gardening in other regions; each will require region-specific strategies and plant palettes. Everything depends on where the gardener lives and the conditions in which they are gardening. Thus, what follows is more in the way of a general discussion that might help point in the right direction than a series of rigid prescriptions.

Organic carbon sequestration is one of the oldest tricks in nature’s ancient playbook for global ecosystem regulation. These days, as we search for ways to pull excess carbon out of the atmosphere in order to mitigate global warming, new attention has focused on “natural climate solutions,” or managing land for carbon sequestration by conserving and restoring ecosystems and changing agricultural and gardening practices. Scientists calculate that these low tech methods could draw down over a third of global carbon emissions by 2030, while simultaneously rescuing ecosystems, strengthening biodiversity, managing water, and mitigating pollution.

So how can gardeners sequester carbon on their own property? It starts with healthy soil. As soil scientist and soil carbon sequestration proponent Christine Jones has said, almost anything done to improve soil health and structure will also increase carbon in the soil. Tried and true management techniques such as adding compost, mulching appropriately in garden beds and around trees, and reducing digging and tilling are vitally important, even fundamental practices when it comes to building healthy soil that develops and maintains good texture, storing carbon both short and long term.

However, there’s more. As I have learned about the ways that plants form ecological communities, I have come to understand that soil management requires attention to garden design and plant palettes as well. Maximum carbon sequestration occurs when multiple species of plants with similar cultural needs form a community with each other, other organisms, and the denizens of the living soil in which they grow. The complex ecological relationships and interactions among these community members literally create and maintain the conditions they themselves need in order to flourish. These interactions also enable short and long-term carbon sequestration. Community health is the reason that boreal and Amazonian forests, as well as wetlands, prairies, woodlands and savannas are able to store so much carbon, naturally. Each of these ecosystems is a different community comprised of yet other different, nested, smaller communities, and carbon storage mechanisms are different in each, yet store carbon they do, in ways we humans haven‘t been able to duplicate.

Consequently, the short answer for would-be carbon gardeners is to garden in such a way that allows plants and the living soil form a thriving, long-term community. Here lies the difference between most conventional gardening and carbon gardening: the latter practices a form of biomimicry by adding ecological functionality into the design mix, making it the premise from which all other decisions flow. Ecological gardeners, those who garden with native plants, garden for birds, pollinators and other wildlife, and regenerative food gardeners who grow organically and consider the needs of pollinators and beneficial insects are already practicing natural climate solutions. Their land is probably already functioning as a carbon sink, rather than being a carbon source, as so many conventionally managed, chemically dependent landscapes are.

But what can be done right now? What are some quick hacks and longer term strategies for ecological community building in the garden?

Ideally, all landscape design would proceed with ecological functionality in mind, incorporating it into every step of the installation and maintenance process. Crucial to carbon gardening is choosing plants with similar cultural requirements that suit the site and the existing soil, and will not require high-carbon inputs such as synthetic fertilizer, weekly mowing, frequent edging and hedge trimming or the use of leaf blowers. Nor would a carbon-storing design call for conservation-inappropriate practices such as weekly watering, leaving soil bare through the winter, or growing water-dependent exotic ornamentals in arid regions. Further, any plant mix should aim for at least 80% native plants. Every region has guilds of native plants—natural companions—that might be suitable for the soil and light conditions of the region’s gardens. And if starting with an established garden, there is no need to rip everything out and start over. Careful assessment and thoughtful changes such as adding native trees and bushes and surrounding them with a mixed understory/groundcover of low-growing perennials—a living mulch—so they can form a community, rather than isolating them in mulch islands, will improve carbon sequestration remarkably soon, though sequestering significant amounts of carbon is not a quick, do-and-done project. While soil will start improving rapidly near the surface, the downward percolation of soluble organic matter and its conversion to stable soil carbon takes longer; but this is what we should strive for.

Additional notes for consideration:

  • Think in four-dimensions. Your four-dimensional space extends as tall as your tallest tree grows, deeper than your plants’ deepest roots delve, and includes the time it takes for the garden community to form the relationships that foster carbon sequestration.
  • If you have room, plant a woodland garden with native trees, shrubs and understory plants. Start with young stock so they can grow together as a community.
  • Or, conversely, plant a prairie/meadow garden with native flowers, sedges and grasses.
  • Improve the soil by adopting management methods that reduce soil disturbance and use of chemicals.
  • Let fallen leaves accumulate under shrubs where they can contribute to soil building and create habitat for overwintering bees and butterflies.
  • Learn to think like a butterfly or a bird or an oak and assess your garden with an eye to what they might need to thrive, then make needed changes.

Get the elements of design, plant selection and maintenance right and a garden becomes not only a deeply effective, carbon-sequestering system, but also by its nature reduces the upstream emissions and carbon inputs or emissions involved in its care. It is amazing to think that the low-tech practices comprising natural climate solutions are more powerful and effective than anything humans have managed to invent for carbon drawdown, but so it is. Even the smallest garden can be vital part of this great effort, and the gardener a powerful climate activist.

Teaser photo credit: In winter, the native plant gardens at the UW Arboretum sequester carbon while adding beauty and habitat. Designed by Darrel Morrison.