Southeast Wisconsin resides in Zone 5, with the northern portion in zone 5a and the southern in zone 5b. This measurement is a standard developed by the USDA that plant growers can determine which plants are likely to thrive and survive in a location.
Side note: I lived in Columbus, Ohio for 8 years before moving back to Wisconsin. They are labeled zone 6, therefore, they can grow more warmer-climate plants. In fact, some plants that I learned about in my classes there aren’t able to survive Wisconsin winters, or our soils. The difference of 10-20 degrees in our winters can have a huge impact on the survivability of plants.
When I moved back here, I was bit ‘home’ sick for the plants that I was used to seeing in landscapes and nature. Plants like, Sassafras (Sassafras albidum), Spicebush (Lindera benzoin), Silverbells (Halesia tetraptera), Passionflower (Passiflora incarnata), and Flowering Dogwood (Cornus florida) are commonplace in Ohio’s Midwest, but not the Wisconsin Midwest I knew as a child. While in Ohio, I worked with a county park system where I sprayed and removed invasive species all summer. I gained a tremendous understanding of plants and identifying what I saw in nature.
These days, I often wonder, “Why don’t we sell X, Y, & Z?” And more, I've come to learn:
I’d be lying if I said some of these truths don't bum me out a little. However, I think about these concerns and realize that we are lucky up here in zone 5.
You see, while central Ohio can support the growth of some bamboo species (Fargesia, Nandina, Phyllostachys), Southeast Wisconsin is riiiight on the cusp of being too cold for bamboo to overwinter. If looking at bamboo, you may find some that say: “This species has exhibited hardiness down to USDA zone 5 when planted in a sheltered location.” At that point, you’re gambling with the viability of a plant in your landscape, much like people do with Japanese Maples and Rhododendrons. I’m not a gambling person.
I mention bamboo because, well, it grows in Ohio. The wilderness I frequented wasn’t overwhelmed by it, but there was commonly frustration between neighbors and bamboo sneaking into the others’ yard. The rapid spread through rhizomes can make control of this plant downright impossible.
Butterfly bush (Buddleia spp.) is another plant that needed to be closely watched in zone 6 because they don't die back to the ground every season. On top of that, they readily reseed and can show up throughout landscapes and wilderness borders. Here in zone 5, the climate causes them to die back each season, like perennials do, and avoids reseeding.
I’ve seen seedlings and saplings of Norway Maple (Acer platanoides) in natural areas in both zone 5 and 6. Norway maples threaten our forests and forest edges with their heavy, annual seed production, while our native Sugar Maple (Acer saccharum) has the tendency to skip a year or two of heavy seed production. In a forest setting, Norway Maple's dense canopy inhibits the growth of most understory plants such as spring ephemerals, ferns, or native seedlings that are regenerating the forest.
I mention these cases of invasiveness because this may be our next invasive battle, especially when it comes to plants on the cusp of zone 5 hardiness. As the purchaser of container plant material, I take this role seriously when it comes to introducing a species to the region. I consider a plants' reputation in states similar to ours, any restrictions in place, and its potential of becoming the next ‘Glossy Buckthorn’.
This is where I feel torn. I have my environmental morals and ethics, and I would love to buy in only native species - never buy another Barberry, flat of Vinca, or Burning bush again! Then, there is the balance of buying in what people want. Supply and demand are at the heart of every business.
If contractors, homeowners, landscape designers desire these plants, I need to supply them these plants. Sure, our salespeople often advise against these plants. However, commonly we are given a plan that needs to be fulfilled. Or, the plants have already been approved by the HOA... The customer is going to use those plants regardless, rather than going through the headache of getting a new plant approved. Designers, contractors, salespeople, and lawmakers can to adjust their mindset and their go-to plants. Change is OK; don't be afraid to update your tools!
At Johnson’s, we actively decrease our quantities of these species with each passing season, and we're seeing declining trends (thankfully!). For example, we proudly grow Wisconsin's native Dwarf Bushhoneysuckle (Diervilla lonicera). In terms of these types of plants, the varieties that we do grow/sell are allowed per Wisconsin’s Invasive Species Rule, Chapter NR 40. That’s not to say they don’t have negative ecological impact and theoretically should also be prohibited. I look forward to the day when we can remove Barberry, Norway Maple, Vinca, and Callery Pear from our ‘need to buy’ list. Until then, check the DNR resource, stay away from using or requesting prohibited/restricted plants, and consider contacting our state representatives to update the Prohibited Plant List.
This tends to be an after-the-fact realization (reactive), usually once it’s too late to control our impact on the surrounding environment. Burning bushes were planted because of the striking red fall color. Callery pears were planted because of the beautiful flowers in spring, and the gorgeous fall color. Invasive plants tend to be quite pretty in a landscape!
This thought isn't meant to stir up emotions, except for maybe concern for our natural areas. We all know our climate is warming - our winters are getting milder and summers are getting hotter. Zones may begin to shift; 6 will become 7, and 5 will become 6. Does this mean we will have the same issues as Ohio? That depends on factors, such as topography, latitude, proximity to coastal areas, and rate of change. I’m sure Ohio will always be more humid, at least where I was, but we aren’t that different.
If we consider the troubles other states near our zone are facing, if we learn our potential for acquiring a new enemy, if we start understanding that our choices will have an impact on our immediate surroundings (positive and negative), then we can avoid a repeat of history here, locally, in Wisconsin's zone 5. We as homeowners, purchasers, contractors, designers, gardeners, can adjust our definition of what we find beautiful and desirable.
The newest, most exotic plant may be the next best thing. Besides the exploitation of a resource, think about the impact it may have on the overall environment if you bring that plant into your landscape. Perhaps, what we’ve had all along is what we should be grateful for?
Um, have you seen the flowers on a Catalpa tree? Who thought you could have the look of a tropical orchid, outside, in a tree, in Wisconsin? What about an evergreen that’s deciduous?! That’s right, we have the Tamarack that while isn’t technically evergreen, it looks like a typical evergreen, but it has the fall color and needle drop like a deciduous tree. Have you seen those trees with the orange berries this time of year (How festive!)? It’s likely a Mountainash (No relation to the Ash (Fraxinus) that’s affected by the Emerald Ash Borer) – why not try this native northwoods tree in your landscape?
Learn more about Beth DeLain in her Staff Bio.