Gardening

How to grow and use milk thistle

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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.


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. So special care and harvesting techniques should be employed when growing milk thistle to make sure the seeds don’t spread beyond your garden.

The ducks of Tyrant Farms staring warily up at a milk thistle flower.

The ducks of Tyrant Farms staring warily up at a milk thistle flower.

More on that below…

Which parts of the milk thistle plant can you eat?

A young milk thistle plant, with hand for size reference. The green and white veined leaves are strikingly beautiful. However, beware that the leaf edges have sharp spikes on them which can easily puncture your skin.

A young milk thistle plant, with hand for size reference. The green and white veined leaves are strikingly beautiful. However, beware that the leaf edges have sharp spikes on them which can easily puncture your skin.

Technically, all parts of the milk thistle plant are edible:

  • 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. 
Milk thistle sun tea being made on a warm spring day.

Milk thistle sun tea being made on a warm spring day.

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. 

Syrphid fly foraging milk thistle. Adult syrphid flies are excellent pollinators and their larvae are voracious predators that consume common plant pests like aphids.

Syrphid fly foraging milk thistle. Adult syrphid flies are excellent pollinators and their larvae are voracious predators that consume common plant pests like aphids.

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.

Milk thistle flowers are quite popular with honeybees.

Milk thistle flowers are quite popular with honeybees.

How to grow milk thistle from seed

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.

A milk thistle flower ripening and about to open.

A milk thistle flower ripening and about to open.

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.

For size reference, the large green plant in this image is a mature milk thistle plant that's about to send up flower stalks. Our Welsh Harlequin ducks are much smaller by comparison.

For size reference, the large green plant in this image is a mature milk thistle plant that’s about to send up flower stalks. Our Welsh Harlequin ducks are much smaller by comparison.

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.

This is about as far developed as you want a milk thistle flower head to be at harvest otherwise the plant will begin dropping seeds.

This is about as far developed as you want a milk thistle flower head to be at harvest otherwise the plant will begin dropping seeds.

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.

A freshly harvested bag of milk thistle flowers with about 6

A freshly harvested bag of milk thistle flowers with about 6″ of stem left on for easier threshing and handling.

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.

Milk thistle seeds, ready to store.

Milk thistle seeds, ready to store.

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 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 interesting that the seeds coming out of this plant have the capacity to stop liver failure due to mushroom poisoning!

How interesting that the seeds coming out of this plant have the capacity to stop liver failure due to mushroom poisoning!

How do you make milk thistle tea?

Milk thistle tea is very easy to make. Here’s how:

  1. Place whole milk thistle seeds in a clean coffee grinder (or mortar and pestle) and grind into powder.
  2. Use about 1 tablespoon of milk thistle seed powder per cup of tea. Place powdered seeds into tea ball.
  3. Pour near-boiling water into cup with tea ball and let steep for 5 minutes, stirring occasionally. 
  4. 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!

KIGI,


More articles you’ll enjoy: 

How to grow and use milk thistle

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