Yes, weeds can have thick stems. Weeds are generally considered to be plants that grow where they are not wanted and compete with other plants for resources like sunlight, water, nutrients and space. While some weeds have thin stems or even no stem at all (like crabgrass), others have very thick ones. For example, the weed known as 'milkweed' has a particularly thick stem that is able to survive in harsh conditions such as drought or freezing temperatures. Other types of weeds such as ragweed and horseweed also feature thick stems which make them difficult to pull out of the ground without specialized tools like weeding forks or hoes. In addition to this, many invasive species of weed also tend to have thicker than normal stems due their ability adapt quickly to new environments - allowing them to outcompete native vegetation for resources while still being able to thrive in hostile soil conditions.