The second species on our list of trees with purple flowers, like the first, is a bit of a misnomer. If you would like to learn more about Colorado’s thistles, Larimer County Weed District has a booklet on Colorado’s thistles, both native and nonnative, at bit.ly/3cuDz1Z.Chaste Tree This shrub has a fragrant smell and will attract many different pollinators. Sharon Bokan is the small acreage coordinator for Colorado State University Extension Boulder County in Longmont. Synthetic herbicides do translocate and kill the root system and may be the best method to manage large Canada thistle infestations. Organic herbicides only burn the leaves on plants but do not translocate and kill the root system, so they are like pulling or mowing the plants. This works for small infestations, but you have to be very persistent, or this method does not work. Some property owners try to manage Canada thistle by pulling or mowing it to keep it from having leaves so it can photosynthesize and store energy in the roots.

If you don’t get every part of the root system, it resprouts.

Trying to dig out the Canada thistle root system is next to impossible. The majority of the Canada thistle plant mass is in the roots, so managing with the root system is the key to eradicating it. You can do this by pulling or undercutting the rosette (first growing season) or cutting off the flower stalk before it has a chance to produce seed (second growing season).Ĭanada thistle is harder to manage, as it lives multiple years and spreads by both seed and roots. All of these thistles are biennials (two growing season growth cycle), with the exception of Canada thistle, which is a perennial.īiennial nonnative thistles are easily managed by keeping them from going to seed. There are five nonnative invasive noxious thistles: bull thistle, Cirsium vulgare musk thistle, Carduus nutans Scotch thistle, Onopordum acanthium and Onopordum tauricum plumeless thistle Carduus acanthoides, and Canada thistle, Cirsium arvense or Breea arvensis. The prickly poppy is in the poppy family Papaveraceae and is a native plant. With the exception of the prickly poppy, all of these are in the same Asteraceae sunflower family as the thistles and are nonnatives. Other plants that may be confused with thistles are prickly lettuce, Lactuca serriola prickly poppy, Argemone polyanthemos, which has a white poppy flower prickly sowthistle, Sonchus asper, and yellow starthistle, Centaurea solstitialis. Native thistle can either be biennials (two growing season life cycle) or perennials (they live longer than two years). Invasive thistles tend to grow taller (4 to 12 feet) and in large, dense stands. If you are above timberline, the thistle is most likely native. Native thistles are usually shorter (less than 4 feet) and have white or paler-colored flowers although don’t base your identification on the flower color alone. Native thistles normally grow singly or in small groups of two to four and not in massive stands like nonnative thistles. Assuming that you don’t want to have to work through a dichotomous key (how botanists identify plants), there are some simple features that may indicate whether a thistle is either native or nonnative.

Purple flowers colorado