Milk Thistle

Silybum marianum

Milk thistle is a spiny white veined plant with sharp spiny flowers and a purple center. This thistle looks quite different from the common thistles we consider weeds in Kansas, is actually quite attractive in the flower garden, and the blooms attract butterflies.   It is not found in the wild in Kansas. The most feared thistle in Kansas, the musk thistle, is Carduus nutans, and another common thistle, the bull thistle, is Cirsium vulgare, are not closely related to the milk thistle.  Milk thistle is one of the top selling herbs world-wide.  Used clinically in Europe for many years, it has only recently become known in the U.S.  The seed is used as supportive treatment for many forms of chronic inflammatory liver disorders, varying from hepatitis to severe Amanita mushroom poisoning (in Germany).

Family:  Asteraceae/Composite
Life cycle:  Annual or biennial
Native:  Mediterranean/Europe
Height:  2-6 feet
Sun:  Full sun
Soil:  Any soil, does well in rocky and dry soil.
Water:  Low water requirement
Flowering:  Flowers are very spiny with purple center and will bloom in mid summer if planted the fall before, and late summer if spring planted. (June-Sept.).
Seed:  No treatment is needed and germination rates are very good. Seed can be planted directly into field in fall or very early spring, or start seed inside and transplant out in late spring.  Transplants are difficult to handle because of the spines.  Transplants probably not worth the trouble as a cash crop, but would work for a garden setting.  Reseeds itself readily, but hasn’t become weedy in our plots, even after several generations of “volunteer” plants.
Spacing:  Plant 12 to 15 inches apart.
Harvesting:  Seed should be harvested when it is brown for maximum medicinal quality.  Using scissors cut off seed head and place into basket, then remove seed from pods and hairs.  Screen out debris.  Can also be mechanically harvested with a wheat combine, but one would want to clean out the combine well after this operation, or have a designated machine for milk thistle harvest.
Parts used:  Seeds, fresh or dried.
Used as:  Tincture, medicinal food, powder, infusion (tea) and capsules.
Food uses:  Stalks can be boiled as a vegetable,  young  leaves used in salads, and the root is also eaten.  Roasted seed can be used as a coffee substitute.
Medicinal benefits:  Although there are some interesting flavonoids and steroids in the leaves of the plant, the main active ingredient in this plant, silymarin, is found only in the seed case.  Silimarin has been shown in laboratory studies to block toxins from entering liver cell membranes, to detoxify liver cells, and even to promote regeneration of liver cells through increased ribosomal protein synthesis.  Clinical studies have not always shown improvement in patients with severe liver damage, but a study of patients with subacute liver disease showed positive results.  Approved in Europe for treatment of upset stomach, liver, and gallbladder complaints.  Used for toxic liver damage, adjunctive treatment in chronic inflammatory liver disease and hepatic cirrhiosis.  Unproven uses include as an antidote to death-cap mushroom poisoning.
Market Potential:   Very High.  This is becoming a very popular herb in the treatment of hepatitis and other liver ailments, and is one of the top selling herbs in the world.  However, prices for the seed may not justify growing the crop and cleaning the seed, with a range of $3.20-$26.50/lb.  Most of milk thistle seed now is imported from Europe and South America.

KSU Field Trial Data - 2000-2002.  

Summary of field trial data:  The milk thistle appeared to be relatively healthy on our field trials, but we didn’t grow it under optimal conditions.  The ideal timing for this plant is to direct seed it in the fall or very early spring (February or March) in Kansas, it will flower in June, and set seed in July.  As a winter annual/biennial, it would be similar in timing to wheat, but doesn’t appear to have a chilling requirement to bloom, as wheat does.  Our plants were greenhouse grown, and transplanted in May, so only had a month or two in the field before flowering and seed set.  Our data at this point consists of top and root dry weight, and we are working on getting an estimate of seed weight as a ratio of the total top dry weight.  For now, we don’t have accurate yield data for the seed for this plant under Kansas conditions. 

Estimates from the literature range from ¼ lb of seed per plant, when hand harvested, which would result in about 4000 lb of seed from a crop density of 21,780 and a survival rate of 75%.  Another literature estimate was closer to 2000 lb of seed dw per acre for machine harvesting.  The seed heads don’t mature at all the same time, so hand harvested yields will be higher than those with a machine, which would be harvested all at once.  With a yield of 2000 lb per acre (which would be similar to 33 bushel wheat),  one would probably not make money at the low end price of $1.60/lb (1/2 of lowest price in Appendix B), but could possibly make money if the price were closer to $13.25 (1/2 of the high end price).  Other questions would have to be answered though, such as whether one has the right planting window in February or March to get the seed in the ground, and the proper equipment to harvest the seed.  From our observations in the field, this plant self-seeds, but doesn’t seem to become weedy, or spread from the immediate vicinity of seed drop.  However, in some places this plant has become weedy, so one would want to be careful where they seeded it, and clean out any harvesting equipment thoroughly before moving on to other crops.