Once you’ve got a vision on the aesthetic you’re wanting to achieve, it’s time to decide what to plant. Selecting species to plant can be a daunting challenge – there are so many options – but you can narrow down the selection. By building a palette of plants to design with, you start the design process on the right foot.
The species you choose are more than just a list of pretty-looking plants, they are the foundation of your design’s success. Taking a little time to work through species selection to create a species palette ensures your landscape not only thrives in your site’s conditions, but also contributes to the broader ecological web, supporting biodiversity and ecological function.
Species selection is all about balance – between ecological function and design goals, between species that thrive and those that might overwhelm, and between plants suited to your site and those that push the limits. With this in mind, let’s break down the essential factors to consider when selecting what to plant.
Ecological Function
Ecological function is our primary consideration when planning a garden. You want to build a palette of plants that provide good ecological function.
Our Native Plant Library is a great resource for filtering by ecological function – We categorize plants in an ecological function through the following labels we’ve come up with:
- KEYSTONE – This is the most impactful category from an ecological standpoint. In ecological terms, a keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Keystone plants host the most diverse range of butterflies and pollinators in an area, driving the base of the local food web.
- SPECIALIST – Plants in this category may not host a large range of insects, but they do have relationships with specialists that rely on a single genus or species for food. Plants in this category go a long way towards sustaining biodiversity in the local ecosystem and are important to include in a design.
- SUPPORTER – Plants in this category don’t host many caterpillars or insects, but they may host a small number or may offer food and shelter for birds.
- LOW IMPACT – The lowest score in our Ecological Function classification. Plants in this category offer little ecologically beyond soil stabilization and shelter for wildlife. They are still fine to use in a design for aesthetic purposes, but we would suggest using them more sparingly.
When choosing species for ecological function, I find it helpful to remember the 80/20 rule, aka the Pareto Principle. This principle states that in any situation, 80% of results come from 20% of causes.
In nature, a keystone species is a good example of this principle (or theory) in action – Keystone species have a disproportionately large effect on their environment compared to their abundance. When creating your plant palette, I always try to make sure 20% of the species I select are keystone species. The rest can be a balance of the remaining ecological function categories.
If you only have a few keystone species you’ve selected, you can also keep this principle in action by using those few species in at least 20% of your designed area. You might only have picked out 3 keystone species out of a palette of 25 species, but by using them in 20% of your planted area, you keep that ecological function in place.
Site Suitability
The second most important consideration is site suitability. By selecting species that are most likely to thrive on your site, you give your landscape the best chance at performing with minimal input.
Site suitability comes down to getting to know your surroundings – If you haven’t already, I recommend reading our article in this series on learning your site characteristics.
For a quick tl;dr of that article, there are three main considerations when selecting plants for your site:
Ecoregion
An Ecoregion is a geographic region marked by similarities in soils, geographic features, and natural plant communities. Ecoregions exist in a hierarchy of increasing detail – At the broadest level are continental ecoregions, narrowing down to regional and finally local ecoregions.
Knowing what ecoregion you are in can help you to narrow down your plant choices. By selecting plants native to your ecoregion, or at least adjacent ecoregions, you give your landscape the best chance at thriving.
Soil Characteristics
Within ecoregions, there may be a variety of microclimates depending on soil types, drainage, and PH – Different plants thrive in clay loam on a hill versus a sandy loam next to a river. Knowing your soil’s PH, drainage class, and general classification can help you to further refine your plant selections to find the plants that are best suited to your exact site.
Light Exposure
The final consideration is light exposure. You want to be aware of the levels of natural light in your garden, and as you solidify your designs, you want to know how those light levels will change as your plantings mature.
Typically with a layered landscape, you’ll start with small trees and shrubs. Planted at proper spacing, there will be a lot of light available – Typically plants native to meadows do well in these settings, but fade out as the larger woody trees and shrubs mature. You want to plan on introducing shade-tolerant species at this point.
If you’re starting with a site that has large mature trees but not much understory or ground layer, you want to plant plants that are more shade tolerant, able to reproduce and spread under the closed canopy of mature trees.
Aesthetic Role
Once you’ve narrowed down your choices to the species that both provide ecological function and will thrive on your specific site, you can then start selecting based on aesthetics. Things like texture, form, and color come into play in this section.
We have come up with a three-label system to help narrow down your designs:
- ANCHOR – This label applies to large trees and shrubs, or tall-growing, large shrubs and plants in grassland regions. These are the largest plants in the landscape, the plants the rest of the design is planned around.
- ACCENT – This label applies to plants that will be planted singly or in small clumps for contrast and impact – Plants in this category may have tall, architectural forms, or brightly colored flowers that stand out in the general planting.
- FILLER – Plants in this category are typically spreading, colonizing plants that are easy to start from cuttings or seed. These plants are planted in large drifts of 7 or more plants for a visual impact, and typically will make up the bulk of your design.
There are of course a lot more attributes to consider when designing – We include an attribute table within our Native Plant Library listings to give a little more detail on things like flower color, foliar texture, and main season of interest.
Plant Vigor
Though perhaps not quite as important as the first three selection criteria, the rate of growth of the plants you choose is important to keep in mind. You want to strike a balance between vigorous growth and overgrowth – By selecting plants that are matched in vigor, your plantings can sort of “keep themselves in check” by competing at an equal rate.
Related to vigor is habit – Some plants grow in clumps, while others spread by roots to colonize an area. If you plant a clump former in with a colonizer, you want to make sure that the clump former is vigorous enough to compete. It also helps if the clump former is a little taller than the colonizer, as this enables it to compete for light.
The differences in vigor of plants are why it helps to plant in large drifts – This is called “patch dominance” in ecological terms, a phrase which especially applies in forests. If you have smaller drifts, you may have to do a little more ongoing work to make sure each plant has enough room to grow.