Milk Thistle

Silybum marianum

herb

Milk thistle (Silybum marianum) is a bold, statuesque thistle, 3 to 6 ft tall, instantly known by its large, spiny, glossy green leaves dramatically marbled with milky-white veins and its big rosy-purple, spiny-bracted flowerheads. It is grown as a striking architectural plant and, traditionally, for its silymarin-containing seeds. Native to the Mediterranean, it is an easy, drought-tough annual or biennial that self-sows freely - so freely that it is a regulated noxious weed in parts of the western US, where it should not be planted.

✅ Plant alongside

Good neighbors that attract beneficial insects or deter pests

• Borage: A bee-friendly companion that shares the sunny, average conditions
• Calendula: An easy edible flower to grow alongside the bold thistle

🛡️ Pest & disease prevention

Proactive ways to stop trouble before it starts. Tap a name with an arrow for its full guide

• Aphids →

  Hose colonies from the growth; the vigorous plant easily outgrows them

• Powdery mildew →

  Give space and airflow in humid conditions

• Self-seeding

  Not a pest but the real management issue - deadhead the flowerheads before they shed seed to keep it from spreading

🌾 Harvest & storage

Harvest the seeds when the flowerheads have finished blooming and begun to dry: the purple flowers fade and the white pappus (thistledown) starts to show at the top of the head. Cut the heads with gloves, dry them fully in paper bags, then break them open and separate the hard, glossy seeds from the down. Catch them before the heads open fully and the seed blows away. The young leaves and peeled stalks are also traditionally eaten as a cooked vegetable once de-spined.

🥗 Nutrition & benefits

Milk thistle is grown mainly for its silymarin-containing seeds, traditionally ground or steeped; the young de-spined leaves and peeled flower stalks are also edible as a cooked vegetable, like a mild artichoke relative. It is a dramatic ornamental as well - but because it self-sows aggressively and is a regulated noxious weed in several western states, check local rules before planting it.