Annual sow thistle, also known as the common sow thistle, is a widespread annual broadleaf weed reproducing from seeds. It is an invasive weed that can drain other plants of vital nutrients and decrease the productivity of your crops.
The vibrant yellow flowers, produced in late summer into early fall, can be used for medicinal and culinary purposes. The entire plant is edible and can be cooked like a vegetable.
Keep reading to learn all about the annual sow thistle, including how to identify it, why it is considered a weed, what it can be used for, and how to get rid of it when it becomes a problem.
It is believed that this ancient weed originated near the Mediterranean. It is not clear when it was first discovered, but it has had many uses throughout history, dating back centuries.
It has since spread all around the world. Today it is known to occur throughout North and South America, Australia, South and East Asia, Africa, and New Zealand.
In ancient times, the annual sow thistle was used as an herbal medicine to treat a variety of ailments.
The milky sap the plant secretes when cut into was used as a topical cure for warts. The flowers were used to treat skin and eye problems, which is interesting given their now-known nutritional value.
This interesting weed was also used in ancient history to induce labor and quicken a baby’s delivery.
Identifying Annual Sow Thistle
Seedlings are so low to the ground that they are often overlooked until they grow taller.
The leaves of the seedlings have toothed margins and are tapered from a wide tip to a smaller stem toward the base of the plant.
A mature annual sow thistle weed can reach up to four feet tall. The stem of the plants is thick and hollow, containing a milky sap that oozes out of the plant when cut. Its leaves are hairless and have a bluish-green hue.
This plant is easy to identify because of its vibrant yellow flower clusters resembling dandelions.
A noticeable difference between annual sow thistle and dandelions is that sow thistle flowers grow in clusters, while dandelions produce only one flower. The blooms of the annual sow thistle tend to produce clusters of anywhere from one to five beautiful flower heads. These weeds have longer, thicker roots than dandelions.
It can also be identified by its leaves, which vary in appearance. The upper leaves of this weed are smaller than the lower leaves. The lower leaves, which can range from four to eight inches long, have a tapered base. Annual sow thistle leaves also look similar to that of a dandelion plant, but they have more ‘teeth.’
Why is Sow Thistle Considered a Weed?
This plant is considered a weed because it is a very invasive species. It is easily spread and grows nearly anywhere. It thrives in gardens, thanks to the nutritious soil you have created for the plants you want.
Annual sow thistle is more invasive than its lookalike, dandelions, with wildflowers blooming all around the plants and leaves sprouting all along the stems. These weeds are more likely to infiltrate your garden and steal nutrients from the soil, so while they are useful in many ways, it is best to remove them from your garden if you see them.
Annual sow thistle can be extremely hard to remove once it has spread around your garden or lawn. It can drain the nutrients from your garden soil, affecting the productivity of the crops.
This weed’s sweet smell attracts pests, like aphids, tomato hornworms, and nematodes, that could prey on your precious plants if the weed has infiltrated your garden.
Annual sow thistle also hosts a variety of different plant diseases, like powdery mildew, which can transfer to your plants and hinder their growth and productivity if the weed is growing nearby.
How Seeds Spread
The seeds of annual sow thistle are spread easily by the wind. They mature in late summer to early fall.
This weed loves agricultural sites where vegetable crops are grown or have been grown. It thrives in these areas, and as the plant matures the wind blows the seeds from the plant, spreading them around where they will begin growing anew to restart the process all over again.
The white fluffy part of the seed, resembling a dandelion, is responsible for its rapid dispersion in the wind. It doesn’t take much for the wind to blow the seeds off the flowers.
Getting Rid of Sow Thistle
There are a few ways to eliminate this pesky but pretty weed. Which method you choose will depend on if you want to use natural remedies or weed killers to kill annual sow thistle. Natural methods are best if you have weeds sucking the nutrients from other plants in your garden.
You can start removing this weed by digging up as much of the plant and its roots as possible. Once it has matured, it is more difficult to remove the entirety of the plant and its root system, so it’s important to catch it early.
After doing that, you should hoe down any further seedlings and young plants as soon as you spot them, which is the easiest and fastest removal method. This ensures that any pieces of the root system that is leftover in the soil cannot thrive and will eventually die off.
If you are trying to remove annual sow thistle from your lawn, regularly mowing will weaken and kill the weeds over time.
Any weed killer can be used to kill annual sow thistle. To ensure optimal effectiveness, coat the weed leaves with the spray until it leaves small droplets behind. Move down into the roots, spraying thoroughly.
On hot days, spraying weed-killer in the evening is more effective because it has longer to be absorbed by the plant, and the spray doesn’t evaporate with the day’s heat.
On cooler days, it is beneficial to spray the weeds early in the day so it has time to dry onto the leaves before the dew sets in.
Most weed-killers that kill on contact are total weed killers, meaning they will kill any plant they are sprayed on. This is important to remember if you are using weed killer to remove annual sow thistle from your garden.
Some weed killers are made to target weeds without killing your grass if the weeds are taking over your lawn and you’ve had enough but don’t want your grass dying.
Always read the instructions and warnings on the label thoroughly before using the product to ensure safe use.
Uses for Plant
Annual sow thistle flowers are actually edible! A young plant has a mildly bitter but rich flavor, while older plants are more bitter and have a tough texture. The leaves, stems, and flowers can be incorporated into stews, salads, and soups like vegetables.
These plants have nutritional value. They are rich in vitamins and minerals, such as vitamins A, C, and K, and packed with antioxidant power. They contain essential nutrients like zinc, iron, calcium, and manganese.
Annual sow thistle contains fiber, which promotes healthy digestion. Its medicinal values are similar to those of dandelion.
A Beautiful, But Invasive Weed
Annual sow thistle flowers are a beautiful, sunny yellow that draws the eye.
They are lovely to look at, but they are very invasive plants. They grow nearly everywhere around the world, and the seeds are effortlessly spread in the wind looking for their new home. Unfortunately for gardeners, that home is their precious garden.
The versatile but persistent weeds can be removed using natural methods or with weed killers, depending on the area in which they are growing.
Are you interested in other varieties of weeds that grow in your garden? Visit the Common Weeds page on our website to learn about weeds you may see in your garden that are actually beneficial!