In this article, you’ll learn all about milk thistle (Silybum marianum), including how to grow, identify, and use milk thistle seeds as a delicious tea and medicinal plant.
Milk thistle: a pollinator-friendly, invasive weed that’s medicinal food for people
We’ve been growing milk thistle in our garden for over a decade and have come to regard it as one of our favorite pollinator plants and tea producers.
Originally from Europe and Asia, milk thistle is not native to the United States. Like many thistle species, it’s even regarded as an invasive weed by university extension agencies in some states.
Thus, special care and harvesting techniques should be employed when growing milk thistle to make sure the seeds don’t spread beyond your garden. More on that below…
Which parts of a milk thistle plant can you eat?
Technically, all parts of the milk thistle plant are edible, including:
- Roots – the large carrot-like taproots on the young plants can be cooked and eaten before they get too old and fibrous.
- Leaves – the leaves can be cooked and eaten like spinach, although it’s advisable to cut the spines off first.
- Flowers – the young flower stems can be eaten before they mature and hollow.
- Stems – the immature flowers can be used to make sun tea; some people report eating them like their relative artichokes, but that seems like a lot of work relative to the reward, given their relatively small size.
- Seeds – mature milk thistle seeds are the most commonly used edible part of the plant. In our opinion, the mature seeds are the best edible part of the milk thistle plant.
Does milk thistle attract butterflies and other pollinators?
Milk thistle is incredibly popular with pollinators, especially bees and various pollinating fly species like syrphid flies (whose larvae are wonderful aphid predators).
On warm, sunny spring days, we marvel at the number of pollinators visiting our milk thistle flowers. Often, multiple pollinator species are foraging together on a single flower, including our personal favorite: Agapostemon splendens, a native, metallic green ground-dwelling bee.
Skippers and butterflies also frequent milk thistle flowers.
How to grow milk thistle
Milk thistle is an annual, full-sun plant that germinates in late winter in our climate zone (Ag Zone 7b). It flowers and goes to seed from May – early June, after which the plants die.
Each milk thistle flower contains dozens of seeds, which soon fall from the plant as the flower head matures, dries, and begins to turn brown. Due to its tendency to readily reseed if not harvested, it’s earned a reputation as an invasive weed.
The fact that thistle plants also pose a health risk to cattle and other ruminants due to their unique digestive systems, has also earned milk thistle a negative reputation with ranchers and farmers throughout the US.
Again, if you grow milk thistle, this means you’ll want to commit to harvesting 100% of the flower heads before they begin to drop seed. This practice will prevent the plants from spreading.
Here’s how to grow milk thistle from seed in your garden:
1. In Feb-March, you can either direct sow milk thistle seeds in your garden OR start the seeds indoors in containers (biodegradable cells or deep plastic cells). Plant the seeds about 1/4″ deep in organic seed starting mix.
2. Maintain lightly damp soil (not wet) AND temperatures around 70°F (21°C) until the seeds have germinated.
3. Immediately after germination, your milk thistle seedlings will need direct sunlight. At this point, you can either:
- use an indoor DIY grow light system like we use,
- put them in front of a sunny south-facing window, or
- leave them outdoors any time temps are above frost/freezing and bring them indoors any time temps go below frost/freezing.
4. Transplant your milk thistle seedlings outdoors as soon as your last frost date has passed. The sooner the better, so their long tap roots don’t get too wrapped around in the seedling cells.
How big are mature milk thistle plants?
Milk thistle plants can get quite large. Once they reach maturity and start producing flower stalks, they have a similar growth habit to collard green plants, with leaf growth about 3-4′ wide x 3′ tall.
Milk thistle flower stalks can reach up to 4-5′ tall, producing multiple flower heads on each stalk and multiple stalks on each plant.
Warning: Despite their beauty, milk thistle leaves, stems, and flower heads have abundant, sharp spikes on them that can be quite painful. Keep this in mind when considering their planting location(s), or if you have pets and children. You probably don’t want to plant them in high traffic spots!
Can you grow milk thistle in pots?
Yes, you can grow milk thistle plants in pots. Due to the their long tap roots and large size, you’ll want a fairly large, deep pot, probably a minimum 5 gallons volume.
How to harvest and process milk thistle seeds
In our climate, milk thistle flower heads mature from May-June. Once the last flowers ripen their seeds, the plant dies.
Here’s how to harvest mature milk thistle flowers for seed:
1. Wearing protective gloves, cut individual flowers from the stalks once the flowers petals turn brown and before the seeds begin to fall out of the fully desiccated flower head. Leave at least 6″ of stem on the flower heads to make them easier to thresh and handle.
2. Place the flower heads into a paper bag and bring them indoors (or into a garage) to continue to dry – at least 14 days.
3. Once the flower heads have dried, you’ll notice them opening up and the feathery seed attachments and seeds begin to spill out. Wearing gloves, thresh individual flower heads into a container or onto an old bed sheet. This will remove most of the seeds, but some will remain lodged inside the flower heads. These can be carefully removed using a butter knife, but you’ll want to wear gloves if you try to avoid getting pricked by the flower spikes.
4. Using a box fan (or a very windy day), winnow the seeds to separate the seeds from the chaff. Milk thistle seeds are fairly large, about the size of a small sunflower seed.
5. Allow the finished seeds to dry indoors for another 7-10 days before storing in containers. We put our seeds in canning jars with a desiccant packet.
6. We don’t usually advocate putting garden debris in your trash versus your compost bin. However, to prevent the spread of milk thistle via seeds throughout your garden, you may want to toss the spent flower heads in case you missed any remaining seeds.
Does milk thistle have medicinal value?
Yes, milk thistle has proven medicinal value, but more research is needed. Complicating matters, much of the current research is conducted using only one primary milk thistle compound, silymarin, rather than using the entire seed and the potential synergies that take place between the full compounds found therein.
Milk thistle has been used for thousands of years to treat various ailments, particularly liver problems. Modern science is beginning to show that milk thistle has a wide range of health and medicinal benefits.
Integrative Medicine (Fourth Edition), 2018, states:
“The active component of milk thistle, silymarin, has reported antioxidant, antiinflammatory, antifibrogenic, antiproliferative, and immunomodulatory effects in addition to stabilizing hepatocyte cell membranes against free radical attack.103-105 Silymarin is a potent antioxidant. It has been reported to raise hepatic and intestinal glutathione levels by 50% in animal studies106 and to increase levels of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase in other animal models.”
Read summary reviews of the latest research into the medicinal benefits of milk thistle.
Can milk thistle treat mushroom poisoning?
Milk thistle has also proven to be an effective treatment for mushroom poisoning.
Each year, hundreds of people in the US mistakenly eat poisonous mushrooms. Often, these are Asian immigrants who eat aptly named Death Cap mushrooms (Amanita phalloides) due to their similar appearance to edible straw mushrooms popular in Asia.
As it turns out, perhaps the most effective treatment for mushroom poisoning is milk thistle. This treatment method is called the “Santa Cruz Protocol”, thanks to University of California Santa Cruz professor Dr. Todd Mitchell’s life-saving interventions using milk thistle to treat patients who would have otherwise died from mushroom toxicity/liver failure.
How do you make milk thistle tea?
Milk thistle tea is very easy to make. Here’s how:
- Place whole milk thistle seeds in a clean coffee grinder (or mortar and pestle) and grind into powder.
- Use about 1 tablespoon of milk thistle seed powder per cup of tea. Place powdered seeds into tea ball.
- Pour near-boiling water into cup with tea ball and let steep for 5 minutes, stirring occasionally.
- Sweeten to taste with the sweetener of your choice (or not at all).
What does milk thistle tea taste like?
Milk thistle tea has a delightfully smooth, rich, nutty flavor. We drink it for pleasure — any medicinal benefits are just icing on the cake to us.
Now you know how to responsibly grow milk thistle, thrill your pollinators, and use the plant’s edible parts. You can grow your own milk thistle tea using the seeds, and enjoy their health-promoting benefits and delicious flavor.
And rather than treating yourself with milk thistle for mushroom poisoning, we strongly advise you to use our 12 rules of foraging to avoid ever eating a poisonous plant or mushroom in the first place!
More articles you’ll enjoy:
- Stop and eat the roses – how to select and grow edible roses
- Why you should grow and use stinging nettle
- How to grow and eat prickly pear cactuses
- 50+ fruits, herbs, and veggies that grow in shade
- Hibiscus: a tasty addition to your edible landscape or garden
- How to grow your own caffeine (or discover it in your yard)
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SandraSeptember 29, 2022 at 12:45 am
Wow! This has been so helpful. I want to buy milk thistle supplements but want to make sure the milk thistle is from the U.S. Do you know of any good milk thistle supplement suppliers that don’t import ingredients?
Aaron von FrankSeptember 29, 2022 at 12:15 pm
Glad this info was helpful for you, Sandra! Since we grow our own milk thistle, we haven’t had need to dive too deep into US-based suppliers. We’d recommend first identifying a USDA-certified organic product as a starting point, then seeing if you can find information about sourcing on the company’s website. If they don’t provide that information, it may be cause for suspicion as to whether their milk thistle is sourced in the US. However, you could always reach out to their customer service to find out for sure. Hope this helps and good luck!
EckardJune 28, 2021 at 4:17 pm
Do St Mary’s Thistles always have white veined leaves
Aaron von FrankJune 29, 2021 at 7:08 am
Yes, white veined leaves are one of the key characteristics of milk thistle (Silybum marianum) plants, which are also called Saint Mary’s thistle.
MEGUMI EMOTOAugust 19, 2021 at 7:38 pm
Hi! I’m looking for milk thistle plant with pink flowers on it.
Do you have any suggestions where to purchase them? I know it’s end of season but I was hoping to find it somewhere.
Aaron von FrankAugust 20, 2021 at 12:34 pm
Hi! Here’s a good source to purchase organic milk thistle seed: https://www.johnnyseeds.com/herbs/milk-thistle/milk-thistle-organic-herb-seed-890.html.
SimbaMay 14, 2021 at 11:46 am
There are many wild milk thistles where I live, nowadays their seeds are unripe, white and easily crush by hands, are they edible and as useful as matured seeds if I eat them? Because I have little liver problems
Aaron von FrankMay 15, 2021 at 8:08 am
Wild thistle seeds are edible. As to whether they contain comparable concentrations of silymarin and other beneficial compounds as milk thistle, it’s impossible to say without a scientific comparison of the seeds of various species grown in comparable conditions/environments. Like you, I also noticed some white, hollow-feeling thistle seeds on wild plants around us this year (we live in Greenville, SC) and my guess is this was due to the seeds being killed prior to maturity by a really late freeze.
Maxi WiebeMay 9, 2021 at 6:04 pm
Central Kansas Here. I am wanting to grow milk thistle for my own medicine. Where do I buy seeds from for this purpose?
Aaron von FrankMay 10, 2021 at 9:58 am
Hi Maxi! You can buy certified organic milk thistle seeds from Peaceful Valley: link
donna CAVE GINNMay 17, 2021 at 1:51 pm
Hello, By chance this herb grows wild in Western North Carolina and I have organic seed coming in now. If you would like some seeds I would love to send you some for barter or donation small donation. Right now the plants are in beautiful bloom and will be ready to send you in a month. I will be happy to send the seed ASAP but you will have to let them dry in a paper bag. Remember this plant multiplies quickly. One plant can produce many flowers and the roots I am told will be tough to kill off. My plants started a few years ago and this year are producing fast!
I am trying to increase my income so I am testing out the product this year. Please check with your Agriculture exchange before you plant in the ground the may not want you to plant this herb due to its fast growth and nuance that it can cause. Check with Google how to plant new seeds and if you need to let them dry our first. Please reply to [email protected]
Aaron von FrankMay 19, 2021 at 12:59 pm
Hi Donna! Thanks for your offer. We have plenty of milk thistle seed. Grow it once, and you can collect enough seed for a lifetime – ha!
I love plantsApril 28, 2021 at 11:33 am
Don’t forget that the white sap is a folk medicine for skin cancers. There is def university research happening to make “official” what humans figured out for their folk medicine thousands of years ago 😀
Aaron von FrankApril 29, 2021 at 9:39 am
Often times, yes. There are also some folk remedies that haven’t really stood the test of time. For instance, modern science tells us that drinking liquid mercury isn’t a good idea nor does it confer immortality, but that information comes a little late for Qin Shi Huang. Ha. 😛
ScottJanuary 16, 2021 at 6:42 am
What about the fan leaf? Not the flower buds. Can the leaves be used for tea too?
Aaron von FrankJanuary 16, 2021 at 11:59 am
Hi Scott! Milk thistle leaves are edible as well. They’re best eaten young, cooked, and with spines removed. So it’s safe to assume you could also use the thistle leaves for tea, although we can’t attest to their flavor since we’ve never used them in tea. You’d probably want to use them in a mix with a more flavorful herb such as mint.
cortijomanDecember 7, 2020 at 7:39 am
If you want to make thistle seeds a lot more palatable just toast them for a couple of minutes without oil in a pan. They go from being a slightly weird challenge for your teeth to a delicious snack. I bought a kilo of seeds online and next year I will be following your advice on how to grow them.
Aaron von FrankDecember 7, 2020 at 10:58 am
Good milk thistle tip, thank you! We’ll give this a try.
Donna Cave GinnMay 17, 2021 at 2:07 pm
I moved to Western NC where Milk Thistle grows wild. We love feeding the pollinators and the yellow finches with this herb. This year we are going to cultivate the seeds if the birds leave any. The leaves on these plants are not was wide as your pictures are they still able to be eaten? Also, how do I prepare the stems to eat? How and when do I harvest the milk? Could I just cut a stem, ( at what age) and dab the milk on precancer lesions? Or do I have to harvest differently? If you could tell me from the time it begins to grow in the spring to the time I may harvest milk would be appriciated!
Aaron von FrankMay 19, 2021 at 1:04 pm
It’s possible that what you’re seeing in the wild is bull thistle (quite common here in the Carolinas) or something similar, not milk thistle. Thistle leaves are best eaten young. Cut off the leaf spikes and use like spinach in cooked recipes. Milk thistle stems are best when very young as well, but harvesting them means no flowers and probably killing the plant. The sap/milk can be accessed at any stage as long as the plants are still green and growing. Once they set seed and begin to die, there’s not much sap to be found. I’m not qualified to recommend milk thistle as a skin cancer treatment and would advise consulting a medical professional about such things.