Key Facts
- A small winter annual in the mustard family
- Produces small white four petaled flowers in spring
- Sets flattened round seedpods that resemble tiny coins
- Commonly found in disturbed and compacted soils
- Tolerant of poor soils and often used or studied as a cover crop and oilseed
- Reproduces by seed and readily self seeds
- Native to Eurasia and widely naturalized in temperate regions
Pennycress (Thlaspi arvense) is a small winter annual in the mustard family that often appears in disturbed or compacted soils. It overwinters as a low rosette, produces small white four‑petaled flowers in spring and spreads readily by seed.
Identification
Look for a low basal rosette of leaves that sends up short flowering stems in spring. Flowers are small and white with four petals. The plant sets flattened round seedpods that resemble tiny coins, which split open to release numerous seeds.
Where to grow and common uses
Pennycress is native to Eurasia and is widely naturalized across temperate regions, so it does well in open, disturbed sites and poor or compacted soils where many garden plants struggle. It is studied and used as a winter cover crop and experimental oilseed because it tolerates marginal soils and reliably produces seed.
Planting time and seasonal habits
As a winter annual, pennycress usually overwinters as a rosette and flowers the following spring. In temperate climates sowing in late summer or fall establishes plants that survive winter and bloom in spring. In milder regions the life cycle can speed up and plants may set seed earlier and spread more aggressively.
Soil, light and watering
Pennycress prefers well drained, disturbed soils and tolerates poor nutrient conditions. It performs best in full sun and will still grow in light shade, but flowering and seed set are most reliable in sun. The plant is not tolerant of long term waterlogging and will decline where soils remain saturated.
Size and hardiness
Plants typically form a low rosette and reach roughly 6 to 18 inches tall when in flower. Pennycress is adapted to a wide temperate range and is reported across USDA zones 3 through 9, overwintering and flowering in colder zones and completing its lifecycle faster in milder areas.
After flowering and controlling spread
Seed production is abundant and volunteers commonly appear near parent plants. Remove seedpods or deadhead before they split if you want to prevent self‑seeding. For larger patches pull rosettes before they set seed or cultivate to reduce seedling cohorts in disturbed ground.
Propagation
Pennycress reproduces by seed and readily self seeds. It establishes from direct seeding or from natural volunteers rather than from cuttings or division.
Toxicity and livestock considerations
Like many Brassicaceae members pennycress contains glucosinolates. It is not widely documented as acutely poisonous to people from incidental contact, but grazing animals may avoid it and consumption of brassica family plants in quantity can affect livestock under some conditions. Check local extension or poison control for region‑specific guidance before allowing access to pastures.
Frequently asked questions
- How fast does Pennycress grow?
- Growth is seasonal. It forms a rosette in the fall and overwinters, then sends up flowering stems in spring and sets seed soon after flowering, so much of the visible growth happens in spring.
- Will Pennycress take over my garden?
- It can naturalize and spread by seed, especially in disturbed or compacted soil. Removing seedpods before they open and pulling rosettes before seed set limit spread.
- When will it bloom?
- Blooming happens in spring after overwintering as a rosette. Exact months vary by local climate and growing conditions.
- How should I water pennycress?
- Keep soils reasonably well drained. Long term waterlogging reduces establishment and plant vigor.
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