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 variety of cardoon, the edible stems of which are eaten. 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 primarily 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).

Most varieties that are appropriate for New England are intended to produce green buds. Some varieties are marketed as having purple buds; these will color best in cool temperatures, and may take on a bronze color in hot temperatures. Beyond color, 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 of 6.5–7.0. 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 Recommendations 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 70ºF–75ºF, using heating mats if needed. Plants require vernalization (exposure to cold temperatures) to induce budding. The most foolproof way to vernalize plants is to move them to a cooler set to 35ºF–50ºF for at least 10 days before transplanting, although the amount of chilling required varies by variety. Research suggests that vernalizing for 500–550 hours (approximately 21–32 days) 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 in early spring (use row cover if frost is expected). However, this is far less reliable than controlled vernalization in coolers, which typically 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 at least 2' between plants in 6' rows. Straw mulch may reduce soil temperatures, which can benefit plants in hot weather. Recent research has shown that the weed control and nutrient retention benefits of plastic and reflective mulch can outweigh the negative effect of elevated temperatures. Plants need 1" of water per week, for which drip irrigation is useful. Overhead irrigation is discouraged since it can foster foliar disease. Artichoke buds should begin to develop in late July.

Perennial artichokes have been successfully overwintered in experimental settings 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 unlikely 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 large enough 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 artichokes, but are often more tender, with fewer tough outer bracts and sometimes lacking a choke, 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 bud 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 desiccate. 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.