Here is everything you need to know about Weeds with Thistles so you can grow these plants and keep them in check.
Thistles are some of the most common weeds that can turn into an invasive nightmare if not cared for properly. Check out these Weeds with Thistles to learn more about these plants.
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What are Thistles?
Thistles are prickly leaves species of Cirsium, Onopordum, and Carduus, which feature dense heads of small, pink, or purple blooms. They can be invasive and non-invasive and sometimes turn into irritating weeds if not cared for properly.
However, these plants are important because Weeds with Thistles are a crucial part of the ecosystem and provide habit and food for various fauna. Weeds with Thistle contain nectar and pollen, which is incredibly valuable to pollinators like butterflies and bees. Many insects and songbirds like pine siskins, dark-eyed juncos, and chickadees also feed on thistle seeds.
Native thistles are extremely valuable since they support healthy populations of beneficial insects. These are killed unknowingly or sometimes out of intent since they are assumed to cause problems. However, Weeds with Thistles are in danger of eradication and must be protected.
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How do Weeds with Thistles Damage Crops?
Weeds with thistles can cause an infestation if left unchecked. For example, just 2 to 5 of these per square meter can diminish cereal yield by 15%.
Furthermore, thistles reduce harvesting efficiency, function as hosts for pathogenic organisms, harbor pests, and infect produce.
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Characteristics of Thistles
Thistles can be annual, biennial, or perennial. These are members of Asteraceae, the Sunflower Family, and are recognized by leaf margins covered in spines and their pink-purple flowers. Thistles have prickly leaves, dense heads of flowers, and spiny stems.
Fun Fact: The national emblem of Scotland is the Prickly Purple Thistle.
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How to Distinguish between Native and Non-Native Weeds with Thistles
You can easily distinguish between Native and Non-Native thistles. If the entire length of the stem is spiny, the bracts are triangular, thick, leathery, and spine-tipped, and the roots are rhizomatous, the weed is a non-native thistle.
On the other hand, if the weed does not have any of the above characteristics, it is likely to be a Native thistle.
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Non-Native Weeds with Thistle
1. Bull Thistle
Botanical Name: Cirsium vulgare
Bull thistle is a biennial that produces deeply lobed hairy foliage; it makes a robust, deep green rosette the first year. This late-flowering thistle variety displays gumdrop-shaped purple blooms from July to September.
2. Canada Thistle
Botanical Name: Cirsium arvense
Native to Europe, this perennial has wavy, lobed foliage with a smooth upper surface. The plant produces clusters of small pink, purple, or white blossoms from June to September.
3. Scotch Thistle
Botanical Name: Onopordum acanthium
This spiny biennial creates dense thickets for cattle to pass into. It produces oblong, broad, lobed foliage covered with hair which gives it a green-gray tint.
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4. Musk Thistle
Botanical Name: Carduus nutans
Also known as nodding thistle, this biennial offers single, heavy flowerheads that sag at maturity; it flowers from June to October and offers purple-pink blossoms.
5. Blessed Milk Thistle
Botanical Name: Silybum marianum
Blessed Milk Thistle is a biennial and sometimes annual; the ridged and branched stems are covered in sparse hairs. The purple bloom heads are large with dark green leaves.
6. Italian Plumless Thistle
Botanical Name: Carduus pycnocephalus
This annual has woolly, spiny-winged stems with upward-pointing branches. The pink-purple flower heads grow in spiny clusters; leaves are deeply lobed.
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7. Scot’s Thistle
Botanical Name: Onopordum acanthium
This biennial is branched and spiny, with a blue-gray appearance with woody, spiny winged stems. The triangular leaves are covered in silver hairs and can be up to 1 foot long.
8. Creeping Thistle
Botanical Name: Cirsium arvense
This most common thistle can be seen on disturbed and cultivated grounds. It has been beneficial for wildlife; the seeds are a crucial source for farmland birds.
Native Weeds with Thistle
9. Clustered Thistle
Botanical Name: Cirsium Brevistylum
This biennial, annual, or short-living perennial has fuzzy stems and cobwebby red-purple flower heads. The shallow-lobed leaves have wooly undersides.
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10. Elk Thistle
Botanical Name: Cirsium scariosum
The Edible Thistle is a biennial or short-living perennial; it looks similar to the clustered thistle. The flower heads are cobwebby with leaves that are wholly on the undersides.
11. Wavy Leaves Thistle
Botanical Name: Cirsium undulatum
This perennial has branched stems coated with white hairs; the solitary, pale lavender to white flower heads are up to 2-3 inches wide. The hairy leaves have wavy margins.
12. Few Leaves Thistle
Botanical Name: Cirsium remotifolium
This biennial or short-living perennial has smooth or woolly stems; it has weak spines. The creamy-white to purple flower heads with deeply lobed and spiny leaves.
13. Mexican Poppy
Botanical Name: Argemone mexicana
This is one of the most recognized weeds we are sure you must have seen growing in your yard. However, it looks quite quirky with its serrated leaves and yellow flowers.
