The thistle is the daisy's less popular cousin. Its purple flowers are attractive and its height impressive. But its thorns and tendency to spread aggressively work against it. Despite its flaws, some gardeners love thistle and couldn't imagine a flower garden without its lavender presence. And why not? Thistle is easy to plant, grow and propagate by root cuttings. Although you are likely to find that thistle has no problem spreading without help.
Dig around the base of the thistle plant with a garden fork. Loosen the soil in a circle around the plant that has roughly a 1 foot diameter. Uproot the plant when the soil is loose to the depth of the rhizome (different for different varieties of thistle), by gently pulling on the plant's base.
Brush or hose the excess soil off of the thistle's rhizomes.
Remove thick, healthy sections of the thistle's rhizome that are 2 to 3 inches in length using a sharp pair of shears. Remove as many sections as you like, but not more than 1/3 of the plant's entire rhizome system.
Plant the rhizome pieces, right side up (the same orientation that they were growing originally), 1 to 2 inches below the soil in full sun. Water the soil so that it is quite moist. Keep the soil moist until the thistle germinates.
Re-plant the thistle plant that you took the cuttings from and water the plant in.