The Native & "Native Adjacent" Mahonias: Why We Love All Four!
By Erica Guttman, WSU Extension Native Plant Salvage/Water resources & habitat program coordinator/educator
Three of Washington’s Mahonia species. Photo by: OSU
At Native Plant Salvage, we get a lot of questions from our friends about why our online plant sales offer so many options within the genus Mahonia.
Let me explain!
Here on the Westside of the Cascade Range, we have two native Mahonias (sometimes still called Berberis, as I learned many years ago!). (1) Mahonia aquifolium (Tall or Short-leaved Oregon-grape, or Oregon Holly-grape) is the species that thrives in lots of sunshine. (2) Mahonia nervosa (Low, Long-leaved, Dull, or Cascade Oregon-grape) is the species that we find in our lowland forests – typically in shade or at the forest edges.
Mahonia nervosa, note many leaflets per leaf and long blooms. Photo by: Erica Guttman
What’s in a name?
I learned these two native species as “Short-leaved” and “Long-leaved” as an easy way to distinguish them: M. aquifolium has many fewer leaflets per leaf (5-9), while M. nervosa has 9-19 leaflets per leaf. Additional features reflected in some common names refer to: M. nervosa having duller, less shiny leaves than M. aquifolium; and M. aquifolium having much more pronounced holly-like foliage (“aquifolium” specifically translates to “sharp-leaved”). And if youreally want to get into the weeds on this, you can look at the veins on the underside of the leaves: “nervosa” refers to the fan-like veins vs. the one central vein on the M. aquifolium. Whew!
What’s “native adjacent”?
We also favor two additional Mahonias that aren’t strictly native in our area: (1) Mahonia repens (Creeping Oregon-grape) is found in forests on the Eastside of the Cascade Crest – forests that are often more open-canopied, where there is typically dappled sunlight. (2) Mahonia aquifolium ‘Compacta’ is a cultivar of our westside Tall Oregon-grape that remains short but thrives in full sun! For a common name, you could go with “Dwarf Tall Oregon-grape,” which sounds a bit incongruous, but it works!
Mahonia aquifolium in flower. Photo by: Erica Guttman
OK, so why bother with more than the two Westside native species?
The reason I like to suggest expanding our view of the Mahonias beyond our two native species reflects both their growth habits and their sun tolerances. Here’s how I think of it:
M. aquifolium thrives in full sun — when you encounter it in its native habitat, it may be at the edges of prairies, in dappled sun in a Garry Oak woodland, or along shorelines outside of tall canopy species. But — wow! — it will get tall! We typically see it around 5-8 feet in most landscapes, but very mature stands in the right conditions can be well over 10 feet tall! And even 8 feet of height won’t work in spots where we need to keep plants low: places where children are being monitored for safety, at traffic circles, rain gardens and other rights-of-way plantings, or even just the edge of a landscape border.
Looking for a shorter option, many folks often force our native shade-loving M. nervosa into full-sun conditions for its low-growth habit — typically 2-3 feet (though taller in old, dense forests). With a lot of water, this is sometimes successful, although often the plants look stunted and “sunburned” during the summer months (think of walking through clearcuts where you see formerly understory species now exposed to full sun). I advocate for drought-tolerant choices, so forcing a native plant into a situation where you need to water the heck out of it doesn’t make sense to me!
Enter the fabulous cultivar, M. aquifolium ‘Compacta’! This has the sun tolerance of our native M. aquifolium, but stays around 3 feet max in height! We wouldn’t use this “not-quite-native” option on ecological restoration sites, but it offers us a lot of flexibility in a landscape setting.
Oregon-grape with fruit and the start of blushing fall colors! Photo by: Mike Melton
Next, you may ask, “Why bring the Eastside M. repens to Westside landscapes?” M. aquifolium is great for sun — with the ‘Compacta’ filling in where we need a lower plant; and M. nervosa can be planted for shady spots. What else is there?
Well, sometimes we have in-between conditions that don’t favor eitherof our Westside Oregon-grapes (or the cultivar) really being able to thrive. And, we love all Oregon-grapes for their stunning evergreen foliage and winter color; their toughness in the landscape; their bright-yellow, fragrant, pollinator-attracting flowers; and their pretty and bird-attracting fruits.
Think about sites that get really hot for just an hour or so right at mid-day or very late afternoon, but are in shade the rest of the time; or spots where there’s dappled light all day long. In those situations, we may find “too much shade” for M. aquifolium — it will get leggy and be unattractive for the landscape; and “too much sun” for M. nervosa — it may need more water to look its best. That’s when I turn to Mahonia repens. (“Repens” attached to plant names connotes “creeping,” typically more prostrate and rooting at the nodes along the ground.)
Although M. repens has a different habit than the others — more of a gently spreading groundcover between 1-3 ft. tall — I have used it to good effect in many lightly shady situations, where it still permits other woody plants, ferns, and herbaceous perennials to politely share the space.
With multiple foliage hues that change with the seasons, Mahonia is a great foil for almost any plant! Photo by: Laura Westrup
Mahonia repens enjoying that dappled light! Photo by: Laura Westrup
Berberdaceae — A great family to explore. This rundown of my favorite Oregon-grapes is just the tip of the iceberg! All of these are in the Barberry family, and if you’re keen on plants, you’ll want to start checking out the options. Most are water-wise and great for wildlife; grow in many different sizes and forms; and offer lots of beautiful and color-diverse foliage, flowers, and berries. You’ll even find some fancy hybrids with our native Mahonias — but that’s another day’s blog post!