Pennycress: The Uninvited Garden Guest You Probably Don’t Want
If you’ve stumbled across small white flowers with distinctive heart-shaped seed pods in your garden or along roadsides, you’ve likely encountered pennycress (Thlaspi). This annual forb might seem innocent enough, but there’s more to this little plant than meets the eye.
What Exactly is Pennycress?
Pennycress is a non-native annual herb that belongs to the mustard family. As a forb, it lacks woody tissue and completes its entire life cycle within a single growing season. The plant gets its common name from its distinctive coin-shaped seed pods that look remarkably like tiny pennies dangling from the stems.
Where You’ll Find This Wanderer
Originally from Europe and Asia, pennycress has made itself quite at home across North America. This adaptable plant has established populations throughout the United States, Canada, Alaska, and even Greenland. You can find it thriving in virtually every state and province, from Alberta to Florida and everywhere in between.
Should You Plant Pennycress in Your Garden?
Here’s the honest truth: most gardeners don’t intentionally plant pennycress, and there are good reasons for that. While it’s not officially classified as invasive in our data, this introduced species has a tendency to show up uninvited and stick around. It reproduces readily on its own and can quickly colonize disturbed soil areas.
The Case Against Pennycress
If you’re considering pennycress for your garden, here are some factors to consider:
- Limited ornamental value compared to native alternatives
- Tends to spread aggressively in disturbed soils
- Can outcompete native plants for resources
- Often considered a weed in agricultural settings
Better Native Alternatives
Instead of pennycress, consider these native options that provide similar ecological benefits without the drawbacks:
- Wild bergamot for pollinator support
- Native mustard family members like field mustard
- Wildflower mixes specifically designed for your region
- Native annuals that support local ecosystems
If Pennycress Shows Up Anyway
Given its widespread distribution, don’t be surprised if pennycress appears in your garden without an invitation. The plant thrives in disturbed soils and can tolerate a wide range of growing conditions. While it does provide some nectar for small insects, the benefits are generally outweighed by its weedy nature.
If you decide to let it stay, keep in mind that it will likely self-seed and return next year. The distinctive heart-shaped seed pods make it easy to identify and remove before it spreads further.
The Bottom Line
While pennycress isn’t the most troublesome non-native plant out there, it’s also not the most garden-worthy choice. For most gardeners, the best approach is to appreciate it for what it is—a hardy survivor—while choosing native plants that better support local ecosystems and provide more ornamental value. Your garden (and local wildlife) will thank you for making more thoughtful plant choices.
