Colorado gardeners, some of the crops you might think are harmless could actually get you in trouble. I was surprised to learn a few of these myself—it’s wild what’s off-limits in the Centennial State.
From unusual plants to common favorites, the rules can catch you off guard. Let’s check out the crops that are surprisingly illegal in Colorado yards.
1. Purple Loosestrife
This beautiful but troublesome plant spreads like wildfire across Colorado’s wetlands. Its vibrant purple flowers might look innocent, but once established, it chokes out native vegetation and disrupts natural habitats.
Colorado authorities actively work to eliminate this invasive species from the state’s ecosystem. The plant produces millions of seeds annually, making it nearly impossible to control once it takes root.
2. Russian Olive
Despite its silvery-gray foliage and drought tolerance, this tree is strictly prohibited in Colorado yards. Many homeowners are shocked to learn that this once-popular ornamental is actually on the state’s noxious weed list.
Throughout Colorado, these trees consume excessive amounts of water and displace native vegetation along riverbanks. Their thorny branches and aggressive growth pattern make them particularly problematic for local ecosystems.
3. Myrtle Spurge
Often mistaken for a harmless succulent, this deceptive plant contains toxic sap that can cause severe skin irritation and even temporary blindness. Colorado has specifically targeted this plant for eradication.
The blue-green rosettes might look attractive in rock gardens, but Colorado officials warn against its aggressive spreading habits. Each plant can catapult seeds up to 15 feet away, quickly turning one plant into a major infestation.
4. Tamarisk
Known for its feathery pink flowers, this thirsty invader consumes up to 200 gallons of water daily! Colorado’s water-conscious regulations ban this plant due to its devastating impact on the state’s precious water resources.
The salt cedar, as it’s sometimes called, secretes salt into the soil, creating an environment where native plants can’t survive. Colorado has spent millions on removal efforts along the western slope’s riverways.
5. Opium Poppy
Those gorgeous red flowers might look innocent, but growing Papaver somniferum in your Colorado garden is a federal offense. Many gardeners unknowingly plant these, mistaking them for legal ornamental poppies.
Federal law enforcement in Colorado doesn’t typically target gardeners with a few plants, but large-scale cultivation will definitely attract attention. The distinctive seed pods contain opium alkaloids that make this beautiful flower problematic.
6. Yellow Starthistle
One of Colorado’s most unwanted plants, this nasty invader forms impenetrable spiny thickets that can injure livestock and ruin pastures. The sharp yellow-flowered menace spreads rapidly through seeds that hitchhike on vehicles and clothing.
Colorado’s agricultural department has designated this plant as a List A noxious weed, requiring mandatory eradication. Just one plant can produce up to 150,000 seeds, making early detection crucial for controlling its spread.
7. Dyer’s Woad
Ancient civilizations prized this plant for its blue dye, but Colorado wants nothing to do with it. The yellow-flowered invader outcompetes native plants and threatens rangeland productivity across the state.
Colorado has placed this historical dye plant on its noxious weed list due to its aggressive nature. Each plant produces up to 10,000 seeds that can remain viable in soil for several years, making complete eradication extremely difficult.
8. Knotweed Species
These bamboo-like plants might seem like perfect privacy screens, but Colorado has banned Japanese, Giant, and Bohemian knotweeds due to their incredibly destructive root systems. They can damage foundations, break through asphalt, and invade sewer lines.
Colorado gardeners often discover too late how aggressive these plants are. Their roots can extend 20 feet deep and 65 feet outward, making removal nearly impossible without professional intervention and specialized herbicides.
9. Dame’s Rocket
Often confused with garden phlox, this deceptive beauty with four-petaled flowers spreads aggressively throughout Colorado’s natural areas. Wildflower seed mixes sometimes contain it, unwittingly introducing this invasive plant to new areas.
Colorado has listed this European native on its noxious weed list despite its pretty purple flowers. Each plant produces thousands of seeds that remain viable for several years, allowing it to establish quickly in disturbed soils.
10. Mediterranean Sage
Don’t confuse this with culinary sage! This woolly-leaved imposter with distinctive yellow flowers crowds out native plants and reduces forage for wildlife throughout Colorado’s rangelands and natural areas.
Colorado land managers target this plant for complete eradication whenever discovered. The sage’s sticky seeds attach to passing animals and vehicles, allowing it to spread quickly across the state’s diverse landscapes.
11. Poppies (Certain Species)
Beyond the infamous opium poppy, several other poppy species are restricted in Colorado gardens. These include Oriental poppies and certain California poppy varieties that can become invasive in the state’s unique climate.
Colorado’s Department of Agriculture monitors these plants due to their potential to escape cultivation. While some varieties are permitted, gardeners should always check local regulations before planting anything in the Papaver genus.
12. Absinth Wormwood
Famous for flavoring the controversial spirit absinthe, this aromatic plant with silvery-gray foliage is actually banned in Colorado yards. Its bitter compounds make it unpalatable to livestock and allow it to quickly overtake pastures.
Colorado ranchers particularly despise this plant for its impact on grazing lands. The distinctive sage-like scent might seem appealing in gardens, but its aggressive nature and status on the state’s noxious weed list make it a definite no-go.