It's tough, it's spiny, it's hairy, and it's taking over your garden. Thistle is a difficult weed to eliminate from your lawn or garden once it has taken hold, and exterminating the weed for good may take several years, because thistles are either biennial or perennial. If you have thistle one year, you will have even more the next, unless you take action. If you want to banish thistle, you'll have to wage war against it. Fortunately, you do have weapons at your disposal.
Pull up as many of the existing thistle plants as you can, both mature plants and seedlings, making sure to get the whole root network. Since mature plants have root systems that can extend for 3 metres (10 feet), you will have better luck pulling up immature plants. Remember: If even a tiny piece of the root survives, the whole miserable cycle can start again.
Mow your lawn short to reduce thistle seed reserve, and keep it that way. It's very important to catch thistle at its early bud growth stage, before it can spread new seeds. Don't let thistle get to the stage in which the stems elongate and begin to produce flowers. Thistles in your garden can be sliced off with a hoe; cut them as close to the ground as possible.
Apply a weedkiller to kill thistle, especially in spring and autumn, before thistles can flower and seed. Use glyphosate weedkillers for your garden, and use a broad-leaf herbicide for your lawn. Since glyphosate kills all plants, you must keep application specific. Use a sponge to apply, or cut thistle plants and then use an eyedropper to put a drop or two into the stem. There are not many natural herbicides for thistles. Some people have reported success with pouring scalding water on thistles or spraying them with straight vinegar.
Put down mulch liberally. It conserves moisture, enriches the soil and prevents germination of new thistles.
Prevent new thistle invasion by keeping lawns thick; reseed disturbed areas. Keep gardens healthy and pest-free, and pull up any new thistle plants as soon as they appear.
Try to attract painted lady butterflies to your garden. They feast on thistle and can significantly reduce the population.
To avoid burns, use extreme caution if pouring scalding water on thistles.
Wear thick gardening gloves when weeding thistles to avoid being cut by their spines.
Always wear gloves when applying herbicides.
Read herbicide labels carefully.