Canadian Thistle is invading my garden beds, and it is spiny and hardy

When it is fairly young, water the area really well and they are easy to pull up. If they are older, the root will be tougher and harder to pull without breaking. Cut it off fairly close to the ground and paint on the weed killer of your choice to the open cut. This seriously decreased the time and space so that the killer gets to the roots quicker. By painting it on rather than spraying, none of the keeper plants in your garden are over sprayed and will not be affected one bit. Make sure while you are caring for your garden, do not let any go to flower or it will get worse than ever. Look around and see if you can see where the seeds came from that got into your garden.