Cardoon

Start cardoon indoors 6 to 8 weeks before last frost

Sow cardoon seed indoors 6 to 8 weeks before your last frost date, 2 to 3 seeds about 1/4 inch deep per cell in plug trays or individual pots, and germinate warm at 70 to 80 F. Keep the mix moist until emergence, then thin to the strongest seedling. Direct seeding in the field works too, but transplants give the best crop because cardoon needs the full season to size up. Note that the 1 inch covering depth in OSU's sheet refers to backfilling the field trench around seed or transplants, not to how deep to sow in a plug tray. Cardoon needs roughly 120 to 150 days from planting to reach harvest, and it is frost sensitive at both ends of the season, so the head start indoors is what buys a cold-climate grower a crop at all.

Set cardoon out after frost danger, and give it far more room than you think

Transplant once the danger of frost is past. Space plants 18 to 24 inches apart in rows 36 to 48 inches apart, setting them into an 8 to 10 inch deep trench and filling soil in around the stems as the plants grow. Pick a full-sun site with deep, well-drained soil, sheltered from strong wind. Cardoon is frost sensitive and deep rooted, and a single plant can reach 3 to 4 feet tall and 4 to 5 feet wide by season's end, so crowding it costs you stalk size. The trench lets you hill soil up the stems, which starts blanching the lower petioles for free.

⚠ Mature leaves carry heavy yellow spines along the petioles on most varieties. Wear gloves and long sleeves when handling anything but a named spineless type.

Keep water uniform or the stalks turn pithy

Give cardoon a uniform supply of moisture across the whole growing period - about 10 to 12 inches of water total, evenly distributed. Soil type does not change the total needed, but it does set the frequency: lighter soils need more frequent applications with less water each time. Leaves and stalks become pithy when the plant is water stressed, and pithy mid-ribs are the whole crop lost. This is a texture defect you cannot fix later by watering more.

Feed the nitrogen early, before flower buds form

Work compost or aged manure plus phosphorus, potash, and sulfur into the bed before planting. Apply nitrogen all at once in early spring before buds begin to form - Oregon State's field rate is 60 to 100 lb N per acre, which works out to roughly 1.4 to 2.3 lb of actual nitrogen per 1,000 square feet of garden. Follow a soil test where you have one. Cardoon is grown for tender leaf mid-ribs, and steady, uninterrupted growth is what keeps them tender. Nitrogen delivered early drives the leafy rosette during the window when stalk quality is actually being built.

Scout weekly for aphids on the lower canopy

Check plants weekly through the warm months, looking at lower-canopy leaves for the pale, almost translucent artichoke aphid and for a wet, shiny honeydew film. In UC's artichoke guidelines an average of 3 aphids per leaflet is the point at which treatment is justified. Below that, let lady beetles, syrphid flies, lacewings and parasitic wasps work. In the eastern US also watch for Japanese beetle chewing the foliage. Aphid honeydew grows sooty mold that blocks photosynthesis, and the aphids themselves curl and yellow the leaves you are trying to harvest as stalks. Scouting catches this while predators can still hold the line.

⚠ Do not spray an insecticide on cardoon that is flowering - bees and other pollinators work the flower heads heavily. The insecticide rates in UC's guidelines are for artichoke, a separate crop on the label; cardoon is not automatically covered, so confirm cardoon appears on the product label before any application.

Blanch the stalks for 4 to 5 weeks before you cut

As the leaves near full size, gather them and tie them together near the top, then wrap the plant in burlap, heavy paper, cloth or cardboard to shut out all light. Allow 4 to 5 weeks of blanching, timed so it lands in cool weather, before harvesting. Light drives the bitter compounds in cardoon mid-ribs. Excluding it for several weeks is what converts a bitter, fibrous thistle stalk into the pale, tender, artichoke-flavored heart that is the actual crop.

⚠ Wrap loosely enough to shed rain and let air move. Cardoon is prone to gray mold and root rot, and a soaked, airless wrap invites both.

Overwinter the crown, or grow it as an annual

Cardoon is reliably hardy only in zones 7a to 10b; colder than that, treat it as an annual or try overwintering. To try: cut the plant back to about a foot tall, mound soil or compost over it, cap that with a bushel basket or rose cone, and drape the whole thing with a tarp to shed rain. Pull the covering in spring after snowmelt and see whether it took. The crown is what carries the plant over, and it rots far more readily from winter wet than it dies from cold - hence the tarp. A plant that survives comes back as several denser rosettes and will usually bloom that year.

⚠ In mild-winter regions cardoon self-seeds hard and is a recognized weed in parts of California and a naturalized invasive in several mild climates. Cut the flower heads off before seed sets if you are not saving seed, and dig the full taproot when removing a plant or it will resprout.

Cut just below the crown once blanching is done

Harvest about 120 to 150 days after planting, once the 4 to 5 week blanching period is complete. Cut just below the crown and trim off the loose outer leaves, leaving a trimmed blanched heart roughly 18 to 24 inches long and 2 to 3 inches across. Eat cardoon cooked, never raw. The blanched heart is the only tender part; the outer leaves and green upper stalk stay bitter and fibrous no matter how long you cook them. Cutting below the crown holds the stalks together as one intact heart.

⚠ Hold hearts at 32 F and 95 to 100 percent relative humidity to stop them wilting; good clean hearts keep 2 to 3 weeks. Cardoon grown through hot conditions can be inedibly bitter from the strong compounds heat forms - taste before you commit a large harvest to the kitchen.