Support Your Area's Pollinators By Using Keystone Plants

An understanding of keystone plants is not just a great way to make sure your garden is as enticing as possible to pollinators – it’s critical for the future of key species. We show you how to raise your eco-awareness

Monarch butterfly feeding on aster keystone plant
(Image credit: Maridav / Getty Images)

Understanding the vital role of keystone plants depends on an appreciation of what the word ‘keystone’ means. A keystone is the critical stone in an archway that holds it all together. If you pull it out, the whole arch falls down. That same principle applies to a keystone plant. It’s a native plant superstar that holds the food web together by providing for the needs of the most important species, like caterpillars and pollinators like Monarch butterflies and bees. 

It makes sense that different regions have different keystone native plants. The plants that are native to the coldest parts of the continent are not the same as those growing naturally in tropical forests. We can each play a role in enhancing our natural spaces by opting to plant keystone species for your ecoregion.

What are Keystone Plants?

If the term ‘worldwide web’ makes you think of tech, you’re not alone. But there is another worldwide web that is even more important for the planet’s survival. This web is made up of all of the members of the food chain, plants and animals, as well as pollinators and other useful insects. Some are more important than others. The most important plants to each different ecoregion in the world have been identified and labeled keystone plants.

For example, there are 15 basic ecological regions in North America, each a puzzle piece of the ecological mosaic of the continent. They range from the Arctic cordillera (think Alaska and Canada) to tropical wet and dry forests (think southern Mexico.) Scientists have identified the keystone plants for each area, those plants that play a critical role in holding the ecosystem together by providing nurture for the essential life species. 

Keystone species for a region are native to that region and, therefore, easy to grow. As native plants, they require very little maintenance, if any. Wondering what to do for the world this year? Adding your area’s keystone plants is a wonderful way to begin.

Why Are Keystone Plants Important?

You may wonder why keystone plants are more important than other plants you may love. The simple answer is that these are the plants that make the world go round. They are the native plants that have formed symbiotic relationships with native wildlife over centuries and more, wildlife including the bees, butterflies and moths that pollinate the crops we eat. 

Beefing up the supply of keystone plants by ecoregion enhances the diversity and abundance of essential insect species that provide food for native birds. Reducing keystone plants diminishes the biodiversity of the planet.

Why Keystone Plants Need Your Help

Whether we term these plants keystone plants or super-plants, they need help. Many of the critical plants are endangered, and their loss would have a serious and permanent impact on the planet. In fact, many native plant populations are feeling the pain as their populations have been dramatically reduced by urban sprawl and the continued popularity of non-native and invasive species.

While some keystone plants assist one type of wildlife, other super-plants are essential to multiple species. One good example of an endangered plant is milkweed – a native plant that has been edged out as highways become larger and cities expand. The result is too little pollen to support the monarch and other critical butterfly species. 

You will also have heard about the diminution in the population of bees in the US, as well as other parts of the world. Research indicates that many North American native bee species are picky about their pollen, only accepting pollen from certain native plants. The reduction of native flowering keystone plants is partially to blame for reducing the bee population, making it harder for the crops we need to get pollinated. The use of chemical pesticides is also a factor in this demise.

Support Pollinators In Your Area With Keystone Plants

Gardeners across the world can help save these and other critical species by planting the keystone plants critical to their area. Remember that keystone plants vary by ecoregion. The plant hardiness zones everyone is familiar with have nothing to do with keystone ecoregions. Hardiness zones are based on winter temperatures while ecoregions are areas that have similar characteristics, including climates, soil types, rainfall levels, geology, elevations, wildlife and plants. 

The continent of North America is divided into 15 different broad ecoregions, according to the Environmental Protection Agency (EPA). These are termed Level I ecoregions, and each is further broken down into Level II and III ecoregions, providing tighter maps and additional species details. Manage your own garden by zeroing in on the broad ecoregion, then fine-tuning with the level II and III ecosystem details. Once you determine your ecoregion, you can use resources available online to identify the most important plant keystone species lists for your spot.

Pick Keystone Plants by Ecoregion: an Example

It may be easier to understand the process of determining and planting keystone plants with an example. Let’s look at the California coast. As far as Level I ecoregions go, this area is Ecoregion 11, the Mediterranean California ecoregion. 

You can easily find a list of the keystone plants for the region, but there are not one or two. There are literally dozens of plants, divided into categories like trees, shrubs and herbaceous, as well as a list of the top 30 keystone plant genera for butterfly and moth caterpillar, and the top 30 keystone plant genera for pollen specialist bees. 

A gardener just getting started with their landscape might pick some species from each category to include. If you don’t have room for trees or shrubs, put in some of the butterfly or bee genera.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.