Psychological / emotional perspective: The thistle has a meaning of rebelliousness and spite, but also of affording protection. When dreaming of a thistle we may be being made aware of those qualities, either in people around us or in ourselves.
The colour of the thistles may also be important.... Dream Meanings of Versatile
Herbs, whether for their medicinal power or their venom, appear frequently in legends and folktales. || To dream that you are lying on grass reveals the need to reestablish contact with yourself. You are wasting life by following some rules that are, by all indications, unnatural. The dream invites you to not lose hope for a major transformative change. However, if your oneiric images show dry, wilted grass, it is an unfavorable sign: it means you feel defeated and you’ve given up on harboring new ideas. Weeds also represent your worst habits and attitudes. These may come from your interior or from others. Most likely, the dream is showing you the way to regain harmony.
If in your dream you are pulling out weeds and they do not contain nettles or thistles, the signs are good. Soon you will be very lucky.... The Big Dictionary of Dreams
Plants are symbols of the power of nature and, in the words of Jung, are ‘regarded with awe and contemplated with philosophical wonderment’. Dreams that feature plants can send powerful messages. Plants embody the life force in dreams and represent the union of earth, water and heaven. Ancient peoples thought that each species of plant had specific qualities and this ancestral lore has produced symbolism and interpretation that is still used in dream analysis today.
Plants, and herbs in particular, have many ancient associations. Climbing plants and honeysuckle symbolize ambition; ground elder suggests powerful ambition. Although deadly nightshade is no longer considered a murder weapon, its association with death is still strong. Is there someone against whom you harbor strong feelings? Thistles and brambles are prickly symbols that hint at antagonism on your own part or on the part of others.
If you dream of weeds, they are a powerful symbol of lies and falsehoods. See also FLOWERS; TREES.... The Element Encyclopedia