Globe Artichoke

Introduction

Globe artichoke (Cynara cardunculus var. scolymus) is a plant in the Asteraceae family native to the Mediterranean region.  The harvested portion of artichokes is the immature inflorescence, or flower bud, of which the fleshy bract bases and the heart can be eaten.  Globe artichoke is a domesticated variety of cardoon, which has edible stems instead of buds, and which is still eaten in many regions of the world.  Unharvested artichoke buds will mature into stunning purple composite flowers, much like thistle, that make excellent bee forage or additions to fresh and dried flower arrangements.

Types and Varieties

In mild climates where temperatures do not remain below 50ºF for prolonged periods, globe artichoke is a perennial crop that is propagated vegetatively.  In those settings, artichokes will produce in their first year but yields will greatly increase in following years.  In New England, artichokes are not cold hardy enough to survive winter reliably and therefore must be grown annually from seed.  While most if not all varieties can be grown as annuals, some varieties have been bred specifically to produce many buds in their first year, after a vernalization period (see Planting section).  

Purple varieties will color best in cool temperatures, and may take on a bronze color in hot temperatures.  Spininess (of bracts and leaves) is another important trait to consider when selecting varieties, as spines on some varieties can reach several millimeters in length. 

Soil Fertility

Apply lime according to soil test results to maintain soil pH between 6.5 and 7.0. Artichokes can be grown on a wide range of soils but produce best on deep, fertile, well-drained soils. Lighter soils with poor water-holding capacity should be avoided. Artichokes are moderately salt-tolerant. 

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR Globe ARTICHOKE

Planting

Artichokes should be seeded into 50-cell trays or 3-4” pots about 8-12 weeks before transplanting.  Seeds take 8-12 days to emerge. Germinate at 70-80ºF, using heating mats if needed. If initially seeded into smaller cell trays, they can be potted up at two true leaves.  Plants require vernalization, i.e. exposure to cold temperatures to induce budding.  The most foolproof way to vernalize plants is to move them to a cooler set to 35-50ºF for at least ten days, although the amount of chilling required varies by variety. Research suggests that vernalizing for 500-550 hours greatly increases the proportion of plants that will produce buds. Providing supplemental lighting during vernalization will improve transplant health but it is not strictly necessary; if lighting, be sure to also check seedlings for watering since lighting enables continued transpiration.  Alternatively, transplanting can be timed so that transplants get their chilling time from ambient outdoor temperatures (use row cover if frost is expected).  However, this is far less reliable than artificial vernalization and coolers should have ample space in spring for seedling trays. 

Field Culture

While the vernalization process is somewhat involved, this crop is mostly trouble-free in the field with few pests, and offers New England customers a unique Mediterranean treat. Artichokes are large plants and require ample space: 2-3' between plants in 4-6' rows.  Straw mulch may reduce soil temperatures (which can benefit plants in hot weather), but recent research on straw and plastic mulch effects on artichoke production demonstrate that plastic and reflective mulch benefits (weed control, nutrient retention) can outweigh the effect of elevated temperatures. Plants need an inch of water per week, for which drip irrigation is useful. Pverhead irrigation is discouraged since this can foster foliar disease. Artichoke buds should begin to develop in late July.  If desired, healthy plants with multiple flowering stalks can be split at the end of the season, trimmed to several inches, and planted into unheated high tunnels under row cover for an early June harvest the following year. 

Perennial artichokes have been successfully overwintered in experimental settings (see Northeast SARE project FNE 14-809) in northern New England with a combination of straw mulch and low tunnels.  While it is possible that refinement of this system could result in earlier harvests and higher yields, it is unlikelt that the proportion of plants that survive winter would be large enough to warrant overwintering versus annual production at commercial scale. 

Harvest and Storage

Yields vary based on variety and cultural practices.  Plants commonly produce 10-20 buds each, but only 2–3 of these will be primary buds (those at the tip of flowering stalks).  Primary buds are typically of a large enough size to market individually, greater than 3” in diameter.  The remainder of the buds are “secondaries” and will form at plant axials further down in the plant.  While these are smaller, they are equally delicious., These can be sold by weight, quart container, etc.  Secondary buds can be eaten much like larger artiochokes, but are often more tender, with fewer tough outer bracts making a larger proportion of the bud edible.  Artichokes are marketed in 22 lb cartons, and buds are graded in the following classes: 18s are larger than 4.5" in diameter; 24s are 4-4.5"; 36s are 3.5-4"; and 48s are 3-3.5".  Average primary diameters in New England tend to fall between 3 and 4". 

Buds are ready to be harvested when they feel fairly compact for their size when squeezed.  Bracts of overmature buds will begin to splay apart, and become bitter and tough.  Clip buds with 2-3” of stem attached.  Wearing gloves is recommended for guarding against spines, and because artichoke plant residue can be difficult to wash off.  After harvest, buds should be cooled quickly and stored at temperatures close to 32ºF, but should not be allowed to freeze.  Freeze damage will discolor bracts. Artichokes can last 2 weeks or longer in storage, after which the fleshy bracts begin to dessicate. Weekly or biweekly harvests are sufficient, depending on size classes of the buds being produced and the time in the growing season.  Plants will continue producing (mostly secondary buds) up until a hard frost.