Gardeners considering the wildlife or ecological value of their plant selections have a lot to consider these days.   New information is emerging constantly about the perceived or proven value our landscape plants may provide for wildlife.  While the field of restoration ecology has naturally occurring plant communities to emulate or attempt to recreate in parks, preserves, and other natural areas, there is no exact playbook for what may constitute a high-value, ecological landscape design other than “plant natives.”

Rightfully so, the recent movement to create more ecologically active garden spaces has centered on the use of native plants since research has clearly defined a more beneficial relationship between native flora and fauna than with nonnatives.  However, many gardeners attempting to get on board with the native craze are challenged by the ever-present non-native plants that fill most urban landscapes. Many of us inherit gardens that are already non-native, or others, starting new plantings, are left scouring garden centers to find true native species among a sea of non-native plants.

At conflict for many of us is a nostalgic love from some of the iconic or personally significant nonnatives we’ve always known.  Amid these opposing feelings and challenges arises the question of “How native does my garden need to be?”

So, how many natives do I plant?

My own garden space is a mixture of primarily native but also non-native plants that are remnants of the landscaping I inherited or favorites I couldn’t resist adding new. I often feel a bit guilty for the non-native plants occupying space that could be filled with more ecologically beneficial native species. To console myself, I’ve tried to limit my nonnative selections to plants that have a distinct benefit, such as very early or late bloom periods, unique habitat structure, or, in my most selfish vane, ornamental appeal that is especially pleasing to my family or me.  

In the quest to allay my own grief, I have sought research and recommendations that can help to answer questions about garden composition and the optimal native to nonnative ratio. Over the years, I have run across some good information that may provide basic guidelines for gardeners seeking to benefit wildlife while not going 100% native.

The National Wildlife Federation recommends planting 80% native species and 100% native milkweed species (Asclepias spp.) to meet the requirements for one of their Monarch Pledge programs.

In my own pollinator-focused plantings, it’s not only native that I’ve focused on but also a season of blooms to provide nectar for monarchs and others. The nonnative component in these spaces is typically comprised of plants that extend bloom time or fill in gaps. Native milkweeds are essential, and I have always steered clear of nonnative milkweeds, although they are prevalent in garden centers and have quite attractive blooms. 

A 2018 study conducted in the Washington DC area found that around 70% native plant cover was required for Carolina chickadees (Poecile carolinensis) to find enough food for their young.  In this case, insects were also part of the equation since they are the primary food source for fledglings. Areas with a lower percentage of natives did not provide the diversity of insect life needed to support the young. For various reasons, the researchers suggest that their findings represent a baseline required for most birds to successfully reproduce in urban areas since the large majority (over 90%) rear their young on insects. 

Differing values in the landscape

Even among the native we plant in the landscape, there are differences in the value they provide wildlife. For example, “Keystone” species are defined as the primary species that support an ecosystem. Without them, many ecosystems collapse. A 2020 study examined the relationship between keystone plants and the butterfly and moth caterpillars they support across North America. Findings report that a mere 14% of native plants support around 90% of caterpillar species. 

Knowing that most birds feed their young insects, many of which are caterpillars, this indicates that a small number of keystone plants provide a huge benefit to both bird populations and, for the caterpillars that escape predation, butterfly and moth populations.

As you consider the value of your native plantings, keep in mind the recommendations above for around 70-80% native plants, but also consider the value of the native species you incorporate. A significant impact can come from just a few species if you choose right.