Colorado’s common weeds include bindweed and kochia, which spread quickly in dry conditions. If you live in the Centennial State, you know that weeds can take over your yard fast. This Colorado Weeds Identification Guide will help you spot and manage them before they ruin your landscape.
Weeds here are tough because of the semi-arid climate, high altitude, and intense sun. Some plants thrive where others struggle. Knowing what you’re dealing with is the first step to control.
Let’s get started with the most common weeds you’ll find in Colorado lawns, gardens, and pastures.
Common Colorado Weeds By Season
Weeds in Colorado fall into two main groups: cool-season and warm-season. Cool-season weeds grow in spring and fall. Warm-season weeds pop up in summer heat.
Identifying the season helps you predict when they’ll appear. It also tells you the best time to treat them.
Cool-Season Weeds In Colorado
These weeds germinate in early spring or late summer. They grow fast when temperatures are between 40 and 70 degrees Fahrenheit.
- Cheatgrass – A winter annual that turns brown early. It’s a fire hazard in dry areas.
- Downy Brome – Similar to cheatgrass. It has soft, hairy leaves and seeds that stick to animals.
- Canada Thistle – A perennial with purple flowers. It spreads by roots and seeds.
- Houndstongue – Biennial with rough, tongue-shaped leaves. Its burrs stick to clothing and pets.
Warm-Season Weeds In Colorado
These weeds love the heat. They germinate when soil temperatures reach 60 degrees or higher. They grow through July and August.
- Kochia – A summer annual that looks like a small bush. It turns red in fall and can tumble across fields.
- Pigweed – Also called redroot pigweed. It has broad leaves and a thick taproot.
- Lambsquarters – A tall weed with white, powdery leaves. It grows fast in disturbed soil.
- Bindweed – A perennial vine with white or pink trumpet flowers. It wraps around other plants.
Colorado Weeds Identification Guide
Now let’s look at the most important weeds in detail. Use this section to match what you see in your yard to the pictures and descriptions below.
Bindweed (Convolvulus Arvensis)
Bindweed is one of the most frustrating weeds in Colorado. It’s a perennial vine that grows from deep roots. The roots can go 10 feet down.
You’ll see it climbing fences, garden plants, or just crawling along the ground. The leaves are arrow-shaped. Flowers are white or light pink and look like small morning glories.
Bindweed spreads by seeds and root fragments. Even a small piece of root left in the soil can grow into a new plant. It’s very hard to kill.
Control tips: Pull it when the soil is moist. Remove as much root as possible. Use mulch to block light. Herbicides with glyphosate or 2,4-D work but may need multiple applications.
Kochia (Kochia Scoparia)
Kochia is a summer annual that can grow 6 feet tall. It starts as a small, fuzzy green plant. By late summer, it turns red or brown.
When it dries out, the whole plant breaks off at the base. It tumbles in the wind, spreading thousands of seeds. This is why it’s called “tumbleweed” in some areas.
Kochia is drought-tolerant and grows in poor soil. It’s common along roadsides, in pastures, and in dry lawns.
Control tips: Mow before it sets seed. Pull young plants by hand. Pre-emergent herbicides like pendimethalin can stop seeds from germinating.
Canada Thistle (Cirsium Arvense)
Don’t let the name fool you. Canada thistle is a serious weed in Colorado. It’s a perennial with spiny leaves and purple flower heads.
It spreads by creeping roots called rhizomes. One plant can colonize a large area in a few years. It’s especially bad in pastures and hayfields.
The flowers attract bees, but the plant reduces crop yields. It’s on Colorado’s noxious weed list.
Control tips: Mow regularly to weaken the roots. Apply systemic herbicides in fall when the plant moves nutrients to its roots. Biological controls like thistle head weevils can help.
Pigweed (Amaranthus Retroflexus)
Pigweed is a broadleaf annual that grows 3 to 6 feet tall. It has thick, reddish stems and large, oval leaves. The leaves have a notch at the tip.
It produces thousands of tiny seeds in dense clusters at the top. These seeds can stay in the soil for years.
Pigweed competes with crops and garden plants for water and nutrients. It’s common in vegetable gardens and disturbed areas.
Control tips: Pull it before it flowers. Mulch garden beds to block seeds. Use pre-emergent herbicides in spring.
Lambsquarters (Chenopodium Album)
Lambsquarters is another fast-growing annual. It can reach 6 feet tall. The leaves are diamond-shaped with a white, powdery coating on the underside.
It’s edible and tastes like spinach when young. But it can harbor pests and diseases that affect crops.
Lambsquarters produces a lot of seeds. One plant can make 100,000 seeds. They can survive in soil for decades.
Control tips: Pull young plants easily. Cultivate soil to bury seeds. Use crop rotation to reduce its spread.
Houndstongue (Cynoglossum Officinale)
Houndstongue is a biennial weed. In its first year, it forms a rosette of rough, tongue-shaped leaves. In the second year, it sends up a flowering stalk.
The flowers are small and reddish-purple. They turn into burrs that stick to animals, clothing, and equipment. This spreads the seeds.
Houndstongue is toxic to livestock. It contains alkaloids that can cause liver damage if eaten in large amounts.
Control tips: Pull rosettes in the first year. Mow flowering stalks before seeds form. Herbicides like 2,4-D work on young plants.
How To Identify Weeds In Your Yard
Identifying weeds takes practice. But you can use a simple process to figure out what you’re dealing with. Follow these steps.
- Look at the leaves. Are they broad or narrow? Smooth or hairy? Arranged opposite each other or alternating?
- Check the growth habit. Does it grow upright, crawl along the ground, or climb? Is it a vine, a rosette, or a bush?
- Note the flowers. What color are they? When do they bloom? Are they single or in clusters?
- Examine the roots. Does it have a taproot, fibrous roots, or creeping rhizomes? This tells you if it’s an annual or perennial.
- Consider the location. Is it in a lawn, garden, pasture, or along a fence? Some weeds prefer certain habitats.
Use a weed identification app or a field guide for Colorado. The Colorado State University Extension website has good resources with pictures.
Noxious Weeds In Colorado
Colorado has a list of noxious weeds that are required by law to be controlled. These weeds are invasive and harmful to agriculture, native plants, or wildlife.
If you find these on your property, you must manage them. Here are the most common ones.
Musk Thistle (Carduus Nutans)
Musk thistle is a biennial with large, showy purple flowers. The flower heads nod downward, which is a key identifier. It has spiny leaves and stems.
It invades pastures and rangelands. Livestock avoid it, so it takes over grazing areas.
Control tips: Mow before flowers open. Use herbicides in spring or fall. Biological controls like thistle head weevils are effective.
Diffuse Knapweed (Centaurea Diffusa)
Diffuse knapweed is a biennial or short-lived perennial. It has white or pale purple flowers with spiny bracts. It grows 1 to 2 feet tall.
It produces many seeds that spread by wind, animals, and vehicles. It’s common in dry, disturbed areas.
Control tips: Pull plants before they seed. Use herbicides like picloram. Grazing with sheep can help.
Leafy Spurge (Euphorbia Esula)
Leafy spurge is a perennial with small, yellow-green flowers. It has narrow leaves and a milky sap that can irritate skin.
It spreads by seeds and deep roots. It’s very aggressive and can take over large areas. It’s toxic to cattle.
Control tips: Apply herbicides in spring or fall. Biological controls like spurge flea beetles work well. Grazing with goats can reduce it.
Dalmatian Toadflax (Linaria Dalmatica)
Dalmatian toadflax is a perennial with snapdragon-like yellow flowers. It has waxy, blue-green leaves that look like a succulent.
It spreads by seeds and creeping roots. It’s common in dry, rocky soils and along roadsides.
Control tips: Pull plants carefully to remove roots. Use herbicides like chlorsulfuron. Biological controls like toadflax weevils can help.
Preventing Weeds In Colorado
Prevention is easier than removal. Here are practical steps to keep weeds out of your yard.
- Maintain a healthy lawn. Thick grass crowds out weeds. Water deeply but infrequently. Fertilize in spring and fall.
- Use mulch. A 2- to 3-inch layer of mulch blocks weed seeds from germinating. Use wood chips, straw, or gravel.
- Plant native species. Native plants are adapted to Colorado’s climate. They outcompete weeds and need less water.
- Clean equipment. Weed seeds stick to mowers, shovels, and shoes. Clean them before moving to a new area.
- Monitor regularly. Walk your yard once a week. Pull weeds when they are small and easy to remove.
Weed Control Methods For Colorado
When prevention isn’t enough, you need control methods. Choose the right one for your situation.
Manual Control
Pulling weeds by hand is effective for small areas. Use a weeding tool to get the roots. Do this after rain when soil is soft.
For deep-rooted weeds like bindweed, dig carefully. Remove as much root as possible. Repeat every few weeks.
Cultural Control
Change the conditions that weeds like. Improve soil health with compost. Adjust watering to favor desired plants. Mow at the right height for your grass type.
Chemical Control
Herbicides can be effective when used correctly. Choose a product labeled for your weed type. Follow instructions carefully.
- Pre-emergent herbicides stop seeds from germinating. Apply in spring for summer weeds, in fall for winter weeds.
- Post-emergent herbicides kill existing weeds. Use spot treatments to avoid harming other plants.
- Selective herbicides target broadleaf weeds without harming grass. Non-selective ones kill all plants.
Always wear gloves and eye protection. Keep children and pets away until the product dries.
Biological Control
Some weeds have natural enemies. Insects, fungi, or grazing animals can reduce weed populations. This is a long-term strategy for large areas.
Examples include flea beetles for leafy spurge and weevils for thistles. Check with your local extension office for available biocontrols.
Common Mistakes In Weed Identification
People often confuse weeds with similar-looking plants. Here are some common mix-ups in Colorado.
- Bindweed vs. morning glory. Morning glory has larger flowers and is an annual. Bindweed is perennial with smaller flowers.
- Kochia vs. Russian thistle. Both tumble, but Russian thistle has spiny leaves. Kochia has soft, fuzzy leaves.
- Canada thistle vs. bull thistle. Bull thistle has larger, more spiny flower heads. Canada thistle has smaller flowers and creeping roots.
- Pigweed vs. lambsquarters. Pigweed has reddish stems and notched leaves. Lambsquarters has white, powdery leaves.
Take a photo and compare it to reliable sources. The CSU Extension website has excellent weed identification guides.
Seasonal Weed Calendar For Colorado
Knowing when weeds appear helps you plan control. Here’s a rough calendar for Colorado.
Spring (March-May)
Cool-season weeds germinate. Look for cheatgrass, downy brome, and Canada thistle rosettes. Apply pre-emergent herbicides for summer weeds.
Summer (June-August)
Warm-season weeds grow fast. Kochia, pigweed, and lambsquarters are active. Pull or mow before they seed. Treat perennial weeds with systemic herbicides.
Fall (September-November)
Cool-season weeds germinate again. Perennial weeds move nutrients to roots. This is the best time to apply herbicides for deep-rooted weeds like bindweed and thistle.
Winter (December-February)
Most weeds are dormant. But winter annuals like cheatgrass can grow during warm spells. Monitor and pull if needed.
Resources For Colorado Weed Identification
You don’t have to do this alone. Use these resources to identify and manage weeds.
- Colorado State University Extension – Free fact sheets and identification guides. Visit their website or call your local office.
- Colorado Department of Agriculture – Lists noxious weeds and control requirements. They have a weed mapping program.
- Weed identification apps – Apps like iNaturalist or PlantNet can help. Take a clear photo and compare results.
- Local weed districts – Many counties have weed managers who offer advice and sometimes free biocontrols.
Frequently Asked Questions
Q: What is the most common weed in Colorado lawns?
A: Bindweed and dandelions are very common. But kochia and pigweed also appear often, especially in dry lawns.
Q: How do I identify a weed in my Colorado garden?
A: Look at the leaves, flowers, roots, and growth habit. Compare to pictures in a Colorado weed identification guide. You can also take a sample to your local extension office.
Q: Are there weeds that are good for Colorado gardens?
A: Some weeds like lambsquarters and purslane are edible and nutritious. But they can still compete with your garden plants. It’s best to control them unless you are intentionally growing them.
Q: When is the best time to apply weed killer in Colorado?
A: For perennial weeds, apply systemic herbicides in fall when plants move nutrients to roots. For annual weeds, apply pre-emergents in spring or fall depending on the weed type.
Q: What weeds are toxic to livestock in Colorado?
A: Houndstongue, leafy spurge, and locoweed are toxic. Also watch for poison hemlock and water hemlock. Remove them from pastures immediately.
Final Thoughts On Colorado Weed Management
Weeds are a fact of life in Colorado. But with the right knowledge, you can keep them under control. Use this Colorado Weeds Identification Guide to spot problems early.
Start with prevention. Keep your lawn healthy and use mulch. Monitor regularly and pull weeds when they are small. If you need chemicals, use them carefully and at the right time.
Remember that some weeds are more than just ugly. They can harm your garden, your lawn, and even your livestock. Stay on top of them, and your yard will thank you.
If you are unsure about a weed, ask for help. The CSU Extension is a great resource. They have