As snow melts and ice recedes we look for familiar signs of spring in nature – the strengthening sun, increased wildlife activity, swelling buds on trees and of course, my favorite, spring wildflowers. We will soon be gearing up to protect those spring beauties from another common spring sight: invasive plants in the mustard family. 

A Familiar Family

Plants in the mustard family are fairly easy to spot. The group includes familiar ornamental and food plants such as candytuft, sweet alyssum, broccoli and canola. 

Mustards are usually short-lived herbaceous plants with leaves that are positioned alternately on the stems. Some produce a rosette of leaves before bolting and flowering.  

The distinctive flowers have four petals that form a cross and fruits that are pod-like in various shapes.  

The pungent flavors many people enjoy in horseradish, wasabi and other mustards come from a class of chemical compounds that are unique to this family. These compounds can negatively impact other plants and microbes in the same environment – a complex effect called allelopathy. More on that in a bit...

Weedy vs. Invasive Mustard Plants

Mustards are well-represented in Minnesota, with around 60 species documented in the state. About half of them are introduced (non-native) and many are very common weeds.  

Mustards have many characteristics that make them ”weedy”: 

• They grow fast.
• They flower and set seed early.
• They often occupy disturbed sites – areas that have been highly altered by human and/or natural impacts.

A few non-native mustards like garlic mustard, narrow-leaf bittercress and dame’s rocket are invasive and can spread beyond disturbed ground and cause harm to native plant communities. Because these invasive mustards are already widespread in some Three Rivers parks, we prioritize removing them from areas with high-quality habitat.  

Forest Impacts

We know that certain components of the forest understory are at greater risk from invasive mustards because of their unique biology. 

• Many native spring wildflowers cannot spread to new areas as quickly as invasive mustards can.  
• Invasive plants escape being eaten by herbivores like deer because they don’t taste as good as native plants do. 
• Because mustards have a high tolerance for disturbed soil, they are less likely to be impacted by non-native earthworm activity than native plants are. 

Plants in the mustard family do not grow with fungi in their root systems as many other plants do. These mutually beneficial relationships between fungi and plant (called mycorrhizae) are very important to many forest plants, especially tree seedlings.  

Remember allelopathy as described earlier?  Some of the compounds mustards produce may create an allelopathic effect by suppressing the growth of these fungi or of native plants directly.  

Researchers continue to study the complex interactions in forest ecosystems, and the best available science helps us refine how we manage mustards. Thoughtful removal of invasive mustards remains an important and relatively easy way to keep our forests healthy and diverse.

Ways To Help

You can play a role in protecting our forests. Here are a few ways you can help:

• Help with early detection by reporting small infestations to land managers.
• Be a good neighbor by removing invasive plants from your property. 
• Help prevent the spread of invasives by not moving soil and seeds on your boots, clothing, gear and pets.
• Most of all, continue to support and enjoy our natural areas. 

Here’s to bountiful spring wildflower viewing for many years to come!