Thistles are very stubborn weeds, and if you do not catch them early on, they could take years to get rid of. With enough persistence, however, it is entirely possible to keep thistle in check without having to resort to drastic measures.
Cut the thistle down. Once the thistle reaches its full grown stage, cut it down at its base. The thistle will pop back up eventually, but after cutting it down often enough, the roots will eventually become too stressed and the entire plant will wither.
While cutting and mowing are important all throughout the season, it is especially important to keep up on it during the first three to four weeks.
Cutting thistle down also prevents the thistles from drying out and leaving seeds.
With Canada thistle, regularly mowing and cutting the thistle down causes the thistle to starve to death. The rhizomes in the top portion of soil spread quickly, making the thistle hard to pull, but continual attacks on the thistle can stress the roots and make it impossible for the rhizomes to replenish their food supply.
With bull thistle, trimming the thistle down only works if you can dig out the rosette formation during the first year. During the second year of this biennial plant, you need to cut the stems down to the ground before the thistle ever has a chance to bloom. If you let bull thistle flower, it will likely go to seed before you have any chance to stop it.
For creeping thistle, cut it down when the thistles are 4 to 6 inches (10 to 15.24 cm) long. Usually, this will be around early June. Cut it again when you next notice new shoots coming out.
If you want to improve the likelihood of stopping thistle in its tracks, wait until after the stalks are fully grown before you cut them back. Trimming the thistle early in the spring does not help much since the thistle will still be resilient enough to grow back. By waiting until just before they bud or immediately after unopened buds form, you stun the plant enough to severely inhibit later growth for the season.
On the other hand, it is important that you trim thistle down before its buds open. Once the buds form and open, thistle can send out seeds. These seeds are carried on the wind very easily, which is one reason why thistle is such a stubborn weed.
When you cut thistle down, make sure that you throw away the clippings. Do not try to compost them since doing so can cause seeds and roots to spread, even if the plant has not officially gone to seed yet.
In addition to stressing the thistle, mowing your lawn also promotes healthy grass and makes the area less hospitable to new thistle plants. As such, thistle is less likely to spread through a trim, neat lawn.
Dig out the root. If you only have a few thistle plants to worry about, you could digging out the entire root system by hand. This can be a time consuming practice since the root systems extend deep into the soil and spread wide, but if you are successfully able to get the entire root out, you can get rid of the plant immediately.
Removing the thistle from the root is essential if you are dealing with bull thistle and not Canada thistle. While this process can help with Canada thistle, digging out the rosette of thistle during bull thistle’s first year is a key part of keeping the weed under control.
Digging out the roots is especially helpful if you need to get rid of spear thistles or marsh thistles. These types of thistles have less extensive root systems in the early stages, so if you dig out the spud of the root at an early stage of growth, you might be able to remove enough of the roots to actually make a difference. The spud root will look like a rosette and lie just below the surface of the ground.
Always pull up as many of the roots as possible. Even broken roots can produce new plants, and since the broken roots are no longer connected to one another, they can actually cause even more thistle plants to pop up.
Introduce natural predators. Certain types of mammals and insects eat thistle, and if you introduce these animals to your yard or pasture, they can keep the thistle population under control for you. After a while, the thistle will be so stressed that it will stop growing.
Insects that naturally attach thistle include the adult thistle-head weevil, thistle rosette weevil, thistle-stem gall fly, flower weevil, stem-mining weevil, yellow starthistle bud weevil, and yellow starthistle hairy weevil.
Cattle will eat most species of non-poisonous thistle. Sheep and ponies tend to eat young thistle shoots, and goats, donkeys, and llamas eat creeping thistle at nearly any stage of growth.
Use a non-selective broadleaf herbicide. One of the surest ways to get rid of thistle is to apply a non-selective broadleaf herbicide to the entire area. The disadvantage is that all vegetation in that location will die, so this method should only be used if you are dealing with more thistle than you are yard.
Apply herbicides during seasons of active growth. These include spring and fall.
The best time to apply weed killer is on a sunny day, when the temperature is between 65 and 85 degrees Fahrenheit (18.3 and 29.4 degrees Celsius).
Try an herbicide with glyphosate. When targeting individual thistle plants, it would be better to do so with an herbicide formulated with an ingredient like glyphosate. Apply this plant poison directly to the individual thistle plant by either spraying it or applying it by hand.
Apply herbicides during seasons of active growth. These include spring and fall.
Other popular herbicides known to work against thistle include MSMA, dicamba, MCPA, bromoxynil, and 2,4,-D.
While glyphosate and many other herbicides are technically non-selective, they can be applied specifically to the thistle, so you may not kill off any other plants in the area if you are careful enough.
To apply the herbicide by hand:Put on a thick rubber glove that is free from leaks.
Put a cotton glove over the rubber one.
Mix the herbicide in a container according the the instructions on the label.
Dip your gloved hand into the herbicide, just long enough to soak the cotton glove.
Make a fist over the container to drain excess herbicide.
Gently grasp each thistle, working from the bottom to the top of the plant, to apply a good dose of herbicide.
Note that you might need to apply herbicide multiple times before it completely wipes out the thistle.
Hire a professional. Professional lawn care management companies have access to more powerful means of thistle extermination. They might use a stronger herbicide or try burning the thistle away.
If you want to try burning the thistle away, make sure that you hire professionals who are also licensed burn crews. Be aware that burning will probably kill the other plants in the area, as well, so it should only be used as a last resort.
Pack other plants close together. To prevent more thistle from popping up, any plants you want in your yard or garden should be planted closely together. Doing so limits the amount of free space thistle has to take root in, thereby discouraging its growth.
Setting other plants close together attacks the thistle from both above and below. The root systems of the other plants can compete for nutrients with the thistle, thereby leaving fewer nutrients for the weed to drain. Tall plants can also create shade in the area, and since thistle hates shade, it will be less apt to grow in these new shady spots.
An especially good competitor plant for thistle is alfalfa. Alfalfa sprouts earlier than thistle does, so it can establish itself before thistle has a chance to do likewise.
Amend the soil in your garden or yard so that it suits the needs of the plants you want to grow rather than the needs of the thistle. Thistle grows well in soil with low fertility, so improving your soil with organic materials can discourage thistle growth while encouraging the growth of most other plants.
Remove any buds and flowers. If you are unable to completely mow down the thistle, you should at least cut any unopened buds and new flowers as soon as you spot them. By cutting the flowers off early, you can prevent the thistle from going to seed. When thistle plants cannot go to seed, they cannot spread, and new plants will not develop.
Difficulty can still arise if there is thistle nearby that you cannot control. For instance, if a neighbor has thistle in his or her yard and refuses to keep it in check, the seeds from that yard can still spread into yours via the wind.
Spread mulch. If you have recently cut your thistle down or simply want to stop new thistle from growing, spreading a heavy layer of mulch over your garden or over bare spots in your yard can do the trick. Mulch makes it difficult for plants to access sunlight and blocks out many of the nutrients thistle needs to sprout and thrive.
Mulch can prevent new seeds from sprouting and may also keep any currently established root systems at bay as long as you have trimmed the growth back down to the ground before you apply mulch.
For mulch, consider using pine needles, shredded wood chips, or pecan hulls. Any standard mulch is fine, essentially, as long as you can apply a 2-inch (5-cm) covering of it.
Create a shady cover. Thistle thrives in sunlight and dies in shade. For long-term management, consider planting a large, shady tree in the area generally afflicted with thistle. For a shorter-term solution, construct a temporary shelter that can provide shade to thistle-infected areas. Easy temporary structures can be made with tar paper, sheet metal, or cardboard boxes.
Beware of contaminated materials. Organic materials you spread onto your lawn can contain thistle roots and clippings if you buy from an untrustworthy source. When you buy organic materials, make sure that the seller has a good reputation.<
Materials to watch out for include grass seeds, mulching material, and animal feed.
To improve your odds, use multiple methods of thistle removal instead of relying on one at a time.
Wear gloves when handling thistle. Standard gardening gloves might be too thin and you may find yourself getting scratched up. If this is the case, try using welders’ gloves, which are made of much thicker material.
Things You’ll Need
Thistle weevils, cattle, goats, and other thistle-eating animals
Thick rubber glove
Thick cotton glove
Shady structure or cover
Sources and Citations
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