Cardoon requires a long, warm growing season of at least 100 days, so most growers start their cardoon seed indoors about 8 weeks before their outdoor planting date to give the plants a head start. Once all danger of frost has passed and the soil is warmed (about two weeks after your average last frost is best), transplant your cardoon seedlings out. Make sure to choose a spot with full sun, and rich, well-drained soil with a pH between 6 and 7. Give your cardoons plenty of room! The plants will grow 4 to 5 feet tall and spread just as wide, so allow at least four feet of space between plants.
Cardoon is generally low-maintenance, but make sure it receives at least an inch of water per week to ensure a good harvest of tender stems. In late summer, once you have plenty of thick stalks, it’s time to blanch your cardoon stems, to give them the delicate texture and taste they’re prized for. Gather the stems together in a bundle and wrap them in something that will keep light out. Cardboard, several layers of newspaper, or a dark colored sheet or pillowcase will work. Tie the bundle together with twine, leaving the upper leaves sticking out the top. Leave your plants this way for 3-4 weeks before harvesting. When you remove the wrapping, the stems will be pale colored, and more tender than they would be without blanching.
Harvest cardoon by cutting all the blanched stems off at the base of the plant, then trim the leaves off and compost them. Use your cardoon like celery in soups, or saute it with some olive oil, salt and pepper. Many cooks parboil the stems to reduce bitterness before using them in recipes.
Cardoon is a hardy perennial in USDA zones 7 through 10, but growers in more Northern climates may also be able to overwinter their plants by very heavily mulching them.
Cardoon (Cynara carbunculus) is an insect-pollinated perennial that typically flowers starting in its second year. It needs to be isolated from other varieties of cardoon or artichokes by at least 800 feet to prevent cross-pollination. In some areas of California and the Southwest, there may be naturalized cardoon or artichoke in the environment, so pay attention to what’s blooming in the wild near your garden.
In about 60 days after cardoon’s large, thistle-like flowers are pollinated, the bracts (spiky parts surrounding the flower) will begin to turn brown and silvery-gray pappi (fluffy projections like the ones on dandelion seeds) will begin to emerge from the top of the flower. At this point, the flowers can be cut off and brought inside to finish drying. When the flowers are entirely crunchy and brown, break them open (wear gloves, they’re spiky!), pull the seeds out and separate each one from its pappus. Store the seeds in an airtight container in a dark, dry, and cool location.