Grow Milk Thistle Without Letting this Aggressive Weed Take Over!

It is quite easy to grow milk thistle, so easy that it pretty much grows on its own, which is why it is considered an invasive species in many places. This biennial plant is usually called a weed since it can destroy ecosystems since it outcompetes other plants for space and nutrients. There are species of thistle that are not invasive. However, it is also a pretty ornamental which will give color to your garden. Do not confuse milk thistle with milkweed.

This plant, relative of the artichoke, is native to the south of Europe, Asia and North Africa. It is not native to North America and it is even illegal to plant it in some areas of the United States, including Texas, Oregon and Washington. Milk thistle can be grown in USDA zones 6 through 9.

Silymarin, an ingredient found in this plant, comes from the white sap that oozes from the stem or leaves when crushed. The plant’s name comes from its milky sap and leaf patterns. Legends say that the Virgin Mary dropped her milk on this plant creating the white traces on the leaves. This ingredient gives milk thistle its medicinal properties which have been used for over 2000 years, mostly to treat gallbladder and liver problems. It may also be useful as a cancer treatment and for lactating mothers. This medicinal herb has antioxidant and anti-inflammatory properties.

What is Milk Thistle?

Milk thistle (Silybum marianum) is a biennial plant that grows quite large, up to 5 feet tall and up to 4 feet wide. It has thorny leaves with light green and white markings. Flower blooms are spiky, appearing in shades of purple, pink or red which stand out in any wildflower garden. This plant will flower in the heat of summer, when most flowers wilt and die. Each stalk can produce multiple flowers which are attractive to bees and other pollinating flies.

milk thistle

Milk thistle can be a problem in pastures since it is toxic to livestock. It is very hard to eliminate this weed because it has deep taproots and dense foliage. A single plant can produce more than 6000 seeds. Each flower head contains up to 190 seeds that are viable for nine years. Seeds can germinate in temperatures that range from 32 to 86 F (0-30 C). These seeds can be spread by the wind or carried on clothes or shoes.

How to Grow Milk Thistle?

Wait until the start of summer to plant milk thistle outdoors. This herb is best grown in areas that require heat and drought tolerant plants. Choose an area with full or partial sunlight. Fertile sandy and loamy soil that is slightly dry is the ideal growing medium. This herb is not picky, so most types of soil will suffice. It likes growing in dry and rocky areas, which is not surprising due to its Mediterranean origins.

Soil should be weeded prior to sowing seeds. Use a rake to loosen up the top 1 inch of soil, then spread seeds evenly. Cover the seeds with a little soil to keep them from blowing away. Keep the area damp and moist until seeds germinate.

It is also possible to start your milk thistle seeds indoors using a seed tray and potting soil. Cover them lightly with a layer of soil. Place the tray in a warm area of your house, with a temperature of at least 55 F (12 C).

Water the soil daily until the seeds germinate, which take about two to three weeks. Start your seeds about two months before transplanting them outside, just after the last spring frost. Once established, this plant is very cold hardy and there is no need to protect it from the frost. Plants will bloom a few months after sprouting.

Those who want to grow this herb in a pot should find one that has 8-10 inches (20-25 centimeters) in diameter and 10-12 inches (25-30 centimeters) in depth. Growing this herb in containers may help to stop its aggressive growth habit. Add liquid fertilizer to the water every couple of weeks.

This herb does not have pests or problems, except for the thistle-head weevil beetle which is used to control this species, as well as other varieties of thistle.

How to Harvest Milk Thistle?

Those who grow this plant for ornamental purposes should prune the top stems as soon as the flowers start to deteriorate. Doing so will keep your garden pretty and prevent seeds from flying away and self sowing. Remember that this plant is a heavy seeder so it may invade your lawn and your neighbor’s as well.

Do not prune the flowers if you intend to use milk thistle medicinally, since most remedies require the use of seeds which contain silymarin. Make sure to use thick gardening gloves before touching this prickly plant since its spines can penetrate the skin. Seed production typically starts in the late summer or fall.

Flowers will form a white pappus tuft (silvery-white seed heads) just like dandelion. Wait until the pods develop where there are flowers and cut them. Place the flower heads in a paper bag for over a week until the drying process is done. Once they are dry, shake the bag so they separate from the flower head. Wait another week after the seeds are extracted to finish the drying process.

Can you Eat Milk Thistle?

Seeds are edible, with a slightly bitter taste. Usually they are grounded. Store them in an airtight container.

Leaves can be eaten both raw and cooked, similar to spinach. It is best to consume leaves when they are young, since they are quite thick, but still have a milder flavor. Use them in salads after removing the sharp leaf-spines. Flower buds are edible, similar to artichoke before the flowers open. Young taproots can also be eaten, since older roots will become too fibrous. Be careful when eating milk thistle since it can become high in nitrate in certain soils.