Roadside Pennycress: A Hardy Annual for Challenging Spaces
If you’ve ever noticed small white flowers blooming along roadsides in early spring, you might have encountered roadside pennycress (Thlaspi alliaceum). This unassuming annual herb has quietly established itself across much of the eastern United States, proving that sometimes the most overlooked plants can be surprisingly resilient.
What Is Roadside Pennycress?
Roadside pennycress is a non-native annual forb that originally hails from Europe and western Asia. As a member of the mustard family, it shares characteristics with many familiar garden plants, though it’s considerably more modest in appearance. This herbaceous plant lacks woody tissue and completes its entire life cycle within a single growing season.
The plant gets its common name honestly – you’re most likely to spot it growing along roads, in disturbed areas, and other places where tougher plants fear to tread. Its scientific name, Thlaspi alliaceum, hints at its garlic-like scent when crushed.
Where Does It Grow?
Roadside pennycress has made itself at home across a substantial portion of the eastern United States. You’ll find it growing in Delaware, Georgia, Indiana, Kentucky, Louisiana, Maryland, Missouri, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, and Virginia. It’s particularly fond of disturbed soils and areas where other plants struggle to establish.
What Does It Look Like?
Don’t expect roadside pennycress to win any beauty contests – this plant is all about function over form. It produces small clusters of tiny white flowers in early spring, followed by distinctive heart-shaped seed pods that give pennycress plants their characteristic appearance. The plant typically grows low to the ground, forming patches rather than standing tall like some of its showier relatives.
Growing Conditions and Care
One of roadside pennycress’s most remarkable traits is its ability to thrive where other plants give up. Here’s what this hardy annual prefers:
- Soil: Tolerates poor, compacted, or disturbed soils that would challenge most garden plants
- Sunlight: Full sun to partial shade
- Water: Drought tolerant once established
- USDA Zones: Can grow in zones 3-9 as an annual
- Maintenance: Virtually none – this plant is a true survivor
Should You Plant Roadside Pennycress?
Here’s where things get interesting. While roadside pennycress isn’t likely to cause problems in most gardens, it’s also not going to win any awards for beauty or ecological benefits. As a non-native species, it doesn’t provide the same level of support for native wildlife that indigenous plants offer.
If you’re dealing with a particularly challenging spot – think compacted soil, roadside conditions, or areas where nothing else will grow – roadside pennycress might fill the gap. However, for most gardening situations, you’d be better served by native alternatives that offer similar toughness with added ecological benefits.
Native Alternatives to Consider
Instead of roadside pennycress, consider these native options that can handle tough conditions:
- Wild bergamot (Monarda fistulosa) for sunny, dry areas
- Pennsylvania bitter cress (Cardamine pensylvanica) for a native mustard family alternative
- Small-flowered buttercup (Ranunculus abortivus) for early spring blooms
- Common evening primrose (Oenothera biennis) for disturbed soil tolerance
Pollinator and Wildlife Value
While roadside pennycress does provide some early-season nectar for small pollinators, its benefits pale in comparison to native plants that have co-evolved with local wildlife. The early bloom time can offer a modest food source when little else is flowering, but native alternatives would provide much greater ecological value.
The Bottom Line
Roadside pennycress is neither villain nor hero in the gardening world – it’s simply a plant that’s found its niche in disturbed areas where few others can survive. While it won’t harm your garden, it also won’t provide the beauty or ecological benefits that most gardeners seek. If you encounter it growing wild, you can appreciate its tenacity, but for intentional plantings, native alternatives will serve your garden and local ecosystem much better.
Sometimes the most valuable lesson a plant can teach us is that there are better options available – and roadside pennycress does exactly that by highlighting the superior choices among our native flora.
