Greetings Friends!

This month's The Leaf in Brief is all about allelopathic plants. That's right, some plants get ahead by killing other plants! The plant of the month is Asarum canadense, Canada Wild Ginger. We also share interesting lore about wild ginger roots.

This months video revisits Carrie Hennessy's trip to the Monarch Trail in Wauwautosa, where she discusses butterfly gardening.

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THE POWER OF ALLELOPATHY by Ben French, PropagatorFA

Competition for light, water, nutrients and space can drive plants to extreme measures. Since they don't really have the option to act as animals do, like eating one another or running away, they must resort to more subtle techniques. Some plants grow fast, relying on speed to get ahead of the others. Some plants are shade tolerant, and will bide their time in the dark while the speedy plants slowly die off. Some plants are far more devious, these plants employ a strategy called allelopathy.


As defined by the Meriam-Webster dictionary - Allelopathy: (al·le·lop·a·thy) the suppression of growth of one plant species by another due to the release of toxic substances.


That's right, some plants get ahead by killing the other plants! Yeah, it might not be too noticeable...but it's effective. If you've planted a tomato near a walnut or have seen a forest understory invaded by garlic mustard, then you've witnessed its effectiveness.


Not all plants are allelopathic, and if they are, rarely does the chemical they release kill everything. Many plants find a way to live under the onslaught of deadly chemicals. For example, Walnuts (Especially Black Walnut - Juglans nigra) release a chemical called Juglone, which inhibits growth of many plants including tomatoes, pines, and hydrangeas. However, most maples, junipers, wild gingers and hostas seem to do fine.


Our plant of the month, Canada wild ginger (Asarum canadense) - has been observed to have allelopathic properties. It was even proposed by our Senior Horticulturalist -Michael Yanny- that it may inhibit the growth of buckthorn seedlings in woodland settings. In time with some examples, that fact may boost this plant's value as a restoration and woodland gardening species.


Examples of allelopathic plants include;

Black Walnut - Juglans nigra

Garlic Mustard - Alliaria petiolata

Common Buckthorn - Rhamnus cathartica

Spotted Knapweed - Centaurea maculosa

Nutsedge - Cyperus rotundus

Tree-of-Heaven - Ailanthus altissima

Canada Wild Ginger - Asarum canadense


So, whenever you are planting in a new garden or want to keep certain plants from coming in where they don't belong, consider the power of ALLELOPATHY.

Juglans nigra
Black Walnut 
Alliaria petiolata
Garlic Mustard
Rhamnus cathartica
Common Buckthorn
Centaurea maculosa
Spotted Knapweed

Visit Johnson's Nursery for more information on Black Walnut Toxicity.

Canada Wild Ginger, Asarum canadense
Mature Height: 6-12"   Mature Spread: 18"
Exposure: Partial sun to full shade, Zone 4
Prefers moist, well-drained soil
Canada Wild Ginger 

Asarum canadense

Wisconsin Native 


Try Canada Wild Ginger as a replacement for non-native Pachysandra or Vinca Vine in shady parts of the yard. Even in the dense shade of a woodland setting, this handsome perennial with large downy, heart-shaped, dark green foliage will spread and help combat garlic mustard. Prefers moderately moist to wet well-drained soil, in part to full shade. Usually stays quite low to the ground, but if it's really happy, we've seen it reach hosta-like proportions.
Wild Ginger Roots

You guessed it, Wild Ginger is so named name because of its similarities to Zingiber officinale, the kind of ginger that has been popular for centuries for its culinary and medicinal uses. Though not as zingy in flavor (or technically related), the roots of Canada Wild Ginger are edible too. Native Americans used the roots for flavoring and a variety of medical ailments. However, if you are tempted to dig some up and try it yourself, use it sparingly. All members of the Aristolochiaceae family contain varying levels of carcinogens.


1. Fall Color Swatches
For swatches of fall color, plant mums, winter pansies, flowering kale and cabbage.

2. Compost Piles

Collect all the leaf litter and other items from landscape and garden clean-up to increase your compost piles.

3. Trees and Shrubs

Choose trees and shrubs with edible berries to provide meals for wildlife, or select for bright splashes of fall foliage.

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Butterfly Gardening
from The Dirt, by Carry Hennessy

Carrie takes a field trip to the Monarch Trail in Wauwatosa, WI to show you a great place to do some butterfly watching. Then, she heads back to the nursery to demonstrate how to bring butterflies into your own yard. Watch more. 

Where Ecology Meets Economy

September 17th -- 8am-3:30pm -- Johnson's Nursery  


This forum for green industry and land management professionals includes a day of educational sessions that aims to create personal dialogue and initiate the development of working relationships to help improve the state of our ecological communities.

Registration is required
. Click here for more details.

Landscape Plastics Recycling

October 18th -- 8am-12:00pm -- Johnson's Nursery 


The recent landscape plastics events were a great success. Hundreds of home gardeners and landscape contractors showed up with trailers, trunks, and beds filled with plastic plant containers and plant trays. We ask you to continue save them for October! 



Visit Johnson's Nursery for a more details. 

Visit the archive to read previous issues of The Leaf in Brief

Johnson's Nursery, Inc.
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