Milk thistle (Silybum marianum) is a self-seeding annual flower reaching a height of 2 to 6 feet. Milk thistle has shiny green leaves covered with white vein lines and a purple bloom that is encircled with spiny projections. The seeds of milk thistle have a short, wispy hair-like fringe allowing it to float easily with the breeze. The seed case is used to create herbal compounds believed to help repair liver and gallbladder disease.
Choose a sunny location where water does not stand after a rain. Milk thistle can grow in any soil so amending the soil with organic matter is not necessary.
Work the soil down and across at least 6 inches for loamy soil. If planting in clay soil, work down and across 12 inches. Rake over to break clumps and to level the tilled ground.
Water the soil to a depth of about 2 inches.
Push three to five seeds into the tilled soil to a depth of about 1 inch. Space the plantings 12 to 15 inches apart. Seeds can be planted in the fall or in early spring. The summer bloom time will be delayed about a month with spring planting.
Water every seven to 10 days if there is no rainfall.
Remove all but one or two of the sprouting plants when they are about 2 inches tall. Carefully pull out the weakest plants by holding your fingers at ground level on either side of the sprout to hold the dirt in the place as you pull out the sprout.
Harvest seeds in the fall. Cut off the seed head after it has dried, remove the seeds and then remove the hair-like fringe from the seeds.