How to Root Out Thistles
Know what makes a plant a thistle., Lean how to identify the Carduus group., Know that the Onopordum group also known as Cotton thistles grow into giants quickly!, Recognize Cirsium species from the other species by the flower cluster being loosely...
Step-by-Step Guide
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Step 1: Know what makes a plant a thistle.
A thistle is a garden weed that has leaves that really look like a hybrid between a lettuce in a cactus.
Many species do have a furry down that gives the plant a frosty appearance and many of the ones that are aggressive weeds have purple to pink button shape flowers that do in a way resemble large dandelions only purple.
Also like dandelions, after the flowers are pollinated and die they turn into a fluffy head which the wind blows and spreads the seeds around.
Most of these plants are winter annuals or cold season biennials that germinate (sprout) after a good autumn rain and form rosette or clump of leaves that survive the over winter.
Often the gardener will see baby thistles in the garden even following a big snowfall after the snow melts. -
Step 2: Lean how to identify the Carduus group.
The plants of this group are more delicate looking compared to the other other thistles with small flowers that resemble porcupines in tight clusters on the tip of the stems.
These species also don't have the white fuzz over the plant like the other groups.
This group is annual or biennial.
Nodding Thistle.
Carduus nutans is a biennial meaning it produces a rosette of leaves 1 to 3 feet the first year and flowers than dies the second year after it sets seeds.
The stems in full bloom do indeed droop or nod down due to the weight of the large flowers.
Spiny plumeless thistle.
Carduus acanthoides flowers have distinctive pineapple shape.
Curly plumeless thistle.
Carduus crispus is the baby of the group staying low to the ground with fine leaves and flowers. , These species can reach over 2 feet easily.There are two main species of this group gardeners encounter as weeds.
These thistles have large leaves covered in silvery fuzz and flowers that are really several large flowers in one clump at the top the the stem.
The two listed species can also hybridize with each other and are biennials or short lived perennials.
These plants are very tough and stubborn.
In some areas Cotton Thistles have turned into spiky impenetrable stands.
Onopordum tauricum or Bull Thistle gets it's name for it's fast growth rate! The species has flowers that are more disk shaped and not narrow or vase-shaped.
Onopordum acanthium called the Cotton Thistle is another giant that has more wider leaves than the bull thistle and flowers are more ball shaped. , Also these have a tendency to be more perennial and live several years in the landscape if not controlled.
Cirsium arvense Canada thistle is perennial and this plant has a lot of names for it.
This plant comes from Europe and is not native to Canada.
The plant produces a flat leaf shaped like a skinny oak leaf and covered with the spines of the many thistle species although not so obvious and grey.
Cirsium palustre or Marsh thistle doesn't grow as fast as Canada thistle but it too can form dense colonies if not controlled.
This species can be identified by it's flowers being long and finger shaped and not sphere shaped.
Cirsium vulgare or Spear Thistle is the national flower of Scotland it's used in a lot of Scottish designs and is seen as an ornament on many books.However in America and in some other countries it's a weed problem.
This species unlike the other two Cirsium mentioned in this articles have a small purple tuft while others are more puffed out.
To add confusion this can also be called bull thistle or Scotch Thistle.
Notice that there are other species of Cirsium that are native wildflowers to North American that don't grow as vigorously as the species listed above.
Some of them such as Cirsium occidentale venustum or the Venus Thistle also can make very unique ornamental plants for a bird and butterfly garden.
This silvery thistle plant native to SW United States has stunning red flowers. , The species listed are the main weed pest gardeners have to deal with.
You can treat get rid of these species using the same techniques as for the other thistle weeds.
Other thistle plants are ornamental like Globe Thistles (Echinops), or used in herbal medicines like (Silybum) milk thistle.
In some countries thistles while young are eaten as food like carrots and cardoon/artichokes (Cynara cardunculus) are also thistles. -
Step 3: Know that the Onopordum group also known as Cotton thistles grow into giants quickly!
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Step 4: Recognize Cirsium species from the other species by the flower cluster being loosely clustered and this give flowers the look of a cluster of fireworks.
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Step 5: Realize that there a lot of other weed plants related to thistles that are omitted from this article.
Detailed Guide
A thistle is a garden weed that has leaves that really look like a hybrid between a lettuce in a cactus.
Many species do have a furry down that gives the plant a frosty appearance and many of the ones that are aggressive weeds have purple to pink button shape flowers that do in a way resemble large dandelions only purple.
Also like dandelions, after the flowers are pollinated and die they turn into a fluffy head which the wind blows and spreads the seeds around.
Most of these plants are winter annuals or cold season biennials that germinate (sprout) after a good autumn rain and form rosette or clump of leaves that survive the over winter.
Often the gardener will see baby thistles in the garden even following a big snowfall after the snow melts.
The plants of this group are more delicate looking compared to the other other thistles with small flowers that resemble porcupines in tight clusters on the tip of the stems.
These species also don't have the white fuzz over the plant like the other groups.
This group is annual or biennial.
Nodding Thistle.
Carduus nutans is a biennial meaning it produces a rosette of leaves 1 to 3 feet the first year and flowers than dies the second year after it sets seeds.
The stems in full bloom do indeed droop or nod down due to the weight of the large flowers.
Spiny plumeless thistle.
Carduus acanthoides flowers have distinctive pineapple shape.
Curly plumeless thistle.
Carduus crispus is the baby of the group staying low to the ground with fine leaves and flowers. , These species can reach over 2 feet easily.There are two main species of this group gardeners encounter as weeds.
These thistles have large leaves covered in silvery fuzz and flowers that are really several large flowers in one clump at the top the the stem.
The two listed species can also hybridize with each other and are biennials or short lived perennials.
These plants are very tough and stubborn.
In some areas Cotton Thistles have turned into spiky impenetrable stands.
Onopordum tauricum or Bull Thistle gets it's name for it's fast growth rate! The species has flowers that are more disk shaped and not narrow or vase-shaped.
Onopordum acanthium called the Cotton Thistle is another giant that has more wider leaves than the bull thistle and flowers are more ball shaped. , Also these have a tendency to be more perennial and live several years in the landscape if not controlled.
Cirsium arvense Canada thistle is perennial and this plant has a lot of names for it.
This plant comes from Europe and is not native to Canada.
The plant produces a flat leaf shaped like a skinny oak leaf and covered with the spines of the many thistle species although not so obvious and grey.
Cirsium palustre or Marsh thistle doesn't grow as fast as Canada thistle but it too can form dense colonies if not controlled.
This species can be identified by it's flowers being long and finger shaped and not sphere shaped.
Cirsium vulgare or Spear Thistle is the national flower of Scotland it's used in a lot of Scottish designs and is seen as an ornament on many books.However in America and in some other countries it's a weed problem.
This species unlike the other two Cirsium mentioned in this articles have a small purple tuft while others are more puffed out.
To add confusion this can also be called bull thistle or Scotch Thistle.
Notice that there are other species of Cirsium that are native wildflowers to North American that don't grow as vigorously as the species listed above.
Some of them such as Cirsium occidentale venustum or the Venus Thistle also can make very unique ornamental plants for a bird and butterfly garden.
This silvery thistle plant native to SW United States has stunning red flowers. , The species listed are the main weed pest gardeners have to deal with.
You can treat get rid of these species using the same techniques as for the other thistle weeds.
Other thistle plants are ornamental like Globe Thistles (Echinops), or used in herbal medicines like (Silybum) milk thistle.
In some countries thistles while young are eaten as food like carrots and cardoon/artichokes (Cynara cardunculus) are also thistles.
About the Author
James Webb
Writer and educator with a focus on practical cooking knowledge.
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