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. 

Globe Artichoke Varieties
Green Purple
Green Globe Improved Imperial Star Purple (A)
Imperial Star (A) Violetto
Tavor (A)  
Wonder  
A: bred for annual production

 

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
Globe ARTICHOKE   PHOSPHORUS (P) LBS P2O5 PER ACRE POTASSIUM (K) LBS K2O PER ACRE
SOIL TEST RESULTS NITROGEN (N) LBS PER ACRE VERY LOW LOW OPTIMUM ABOVE OPTIMUM VERY LOW LOW OPTIMUM ABOVE OPTIMUM
Broadcast and Incorporate in fall 100 75 50 0-25 0 150 100 50 0

Sidedress 3-4 weeks later 

0-50

0

0

0

0

0

0
TOTAL RECOMMENDED 120 75 50 0-25 0 150 100 50  0

 

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.

Disease Control

DISEASE CONTROL NOTE: For the disease control products listed below, one product trade name and formulation are provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 25 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients. 
The symbol OG indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more detail.
 

Gray Mold (Botrytis cinerea)

Botrytis cinerea is most problematic iunder wet conditions and as a secondary pathogen. Infected  bracts will typically develop sunken brown lesions, with characteristic gray mold sometimes developing on the inside of bracts. Remove infected plant material and space plants further apart in future seasons to mitigate incidence of gray mold. Preventing insect feeding damage and other wounds can help mitigate the effect and spread of gray mold.

polyoxin D zinc salt (VEGGIETURBO 5% SC)OG: 6.5 to 13.0 fl oz/A; PHI 0d, REI 4h, Group 19; Do not apply more than 4.3 oz. a.i./acre/season (6 applications at maximum rate)
 

hydrogen peroxide plus peroxyacetic acid (Oxidate 2.0)OG: see label for rate; PHI 0d, REI 1h; Group NC; Use as preventative or curative.
 

pyraclostrobin plus boscalis (Pristine): 18.5 to 23.0 oz/A; PHI 0d, REI 12h; Groups 11 & 7; Do not apply as a tank mix and do not make more than 3 applications per year.

Verticillium Wilt (Verticillium dahliae)

The same strain of Verticillium wilt that affects strawberries and lettuce can also infect artichoke. Because this disease spreads through plants’ vasculature, symptoms often appear on only a lengthwise fraction of the plants, and appear as wilting, yellowing, or stunting. Avoid rotating artichokes with strawberries and lettuce.

Insect Control

Aphids, primarily Green Peach (Myzus persicae)

Green peach aphids overwinter in the egg stage on woody plants in the Prunus species (peach, wild cherry, etc.), where nymphs feed in spring. Field vegetable crops are colonized in June by winged females who produce live young (nymphs), resulting in multiple generations of wingless females. Generation time from birth to reproductive adult is 1 to 2 weeks depending on temperature; each female produces 30 to 80 live young. If food quality declines, females develop wings and leave searching for new plants. In fall, male and female winged aphids develop and return to woody plants to mate and lay eggs.

Winged green peach aphids have a black head and thorax and yellow-green abdomen. Wingless adults and nymphs are usually pale yellow-green, including the cornicles (a pair of tubes near the tip of the abdomen), but may be pink. Adults reach 2 mm long. Aphids feed on leaves and excrete a sugary, sticky substance called "honeydew", which fosters growth of black sooty mold fungus.  If using plasticulture, this honeydew will be apparent on the plastic.  Scout the underside of leaves for aphids as plants establish.

Numerous crop families (including solanaceous crops, cucurbits, brassicas, spinach and chard, and carrot families) and broadleaf weeds support green peach aphids. Feeding on young tissue causes curling, wilting, stunted growth, and contamination of harvested crops. The major damage caused by this aphid is the transmission of many plant viruses. It is also a pest in greenhouses; see Vegetable Bedding Plants and Greenhouse Tomato for greenhouse management.

Aphids are usually controlled by natural predators and parasites, such as lady beetles, lacewings, spiders, syrphid fly larvae, wasps, and beneficial fungi, unless the populations of these beneficials are disrupted by chemical sprays. Preserve natural enemies by using selective/microbial pesticides for other pests whenever possible. Occasionally, green peach aphid (GPA) or, less commonly, melon aphid (MA) and potato aphid (PA) populations build up and require controls. Early-season, broad-spectrum sprays will destroy beneficials and lead to aphid population buildup.

Begin to examine plants in early July for aphids and the presence of beneficial species. Spray only when aphids are increasing and building up to high numbers. Coverage of the leaf underside is important. Add a spreader-sticker. Plant crops away from Prunus species. Spray effectiveness may vary depending on the species present. Reflective plastic mulch may help to repel aphids. 

Stink Bug

Stink bugs, similar to thrips and tarnished plant bugs, feed on the base of buds as they develop.  This causes scarring that prevents normal development of the bud in the feeding region, resulting in unmarketable, claw-shaped artichokes.

Tarnished Plant Bug (Lygus lineolaris)

In artichoke, tarnished plant bugs may feed on leaves, leaving behind a shothole appearance.  More significantly, they may feed at the base of buds and, in extreme cases, cause buds to turn black, rendering them unmarketable. See Lettuce for more information about tarnished plant bugs. 

Thrips

The piercing-sucking mouthparts of thrips cause twisting and curling of leaves.  Occasionally, thrips may also feed on bracts of buds, which can become deformed and thus unmarketable.
 

Weed Control

NOTE:  For the herbicides listed below, one product trade name and formulation is provided for each active ingredient along with preharvest interval (PHI), restricted entry interval (REI), resistance management group number, and example of rates and special instructions. In many cases, there are other products available with the same active ingredient. However, not all products with the same active ingredient are registered for use in a crop. Always check the product label to be sure that the crop is listed before using. 

Preemergent Herbicides (before weeds germinate)

flumioxazin (Chateau SW)REI 12h, Group 14. For perennial artichokes, apply 6 oz/A per application, only 1 application allowed per year. Must be applied within 2 days of planting crowns or cutback of mature plants, before crop emergence. For annual or newly established artichokes, apply 4 oz/A per application, only 1 application allowed per year. Must be applied no later than 2 days before transplanting. Activate with water through irrigation or rainfall after transplanting, but not before.

pendimethalin (Prowl H2O)PHI 60d or 200d, REI 24h, Group 3. Apply up to 3 pt/A  (60 day PHI) or 3.1-8.2 pt/A (200 day PHI) per application. Do not exceed 8.2 pts/A per year. Apply to the soil surface at least 1-2 days before transplanting artichokes.

Pre- and Postemergent Herbicides

oxyfluorfen (Goal 2 XL)PHI 5d, REI 24h, Group 14. Apply 4-6 pt/A per application, multiple applications are allowed, 8-10 weeks apart. Do not exceed 6 pts/A per year. Apply as a directed spray to the soil surface between the rows and at the base of artichoke plants in a minimum of 40 gal/A of spray. Can be applied after ditching operations until weeds reach the 8-leaf stage. Contact with spray or drift will cause injury to artichoke fronds or severe injury to buds or flowers.

Postemergent Herbicides (after weeds germinate)

carfentrazone-ethyl (Aim EC): PHI 0d, REI 12h, Group 14. Apply 0.5-2 oz/A per application, multiple applications allowed per year. Do not exceed 6.1 oz/A per year. Apply as a hooded application, as a preplant burndown no later than 1 day before transplanting.

diquat (Reglone): PHI 1yr, REI 24h, Group 22. Apply 1.5-2 pt/A per application. Only use during site preparation prior to planting. Spray weeds 1-6” tall, retreatment may be necessary to control established weeds. Apply in a minimum of 15 gal/A of spray. Do not allow spray to contact crop stems, foliage, or fruit.

glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9. Apply 10 oz to 3.1 qts/A per application. Do not exceed 5 qts/A per year. Rate depends on target weeds, see label for rate selection. Avoid contact with any part of the artichoke or crop death could occur. May apply fallow intervals, prior to planting or transplanting, at planting, or before crop has emerged. Could cause injury when applied prior to transplanting or direct-seeding into plastic mulch. Remove residual product from plastic mulch with a 0.5” of water through irrigation or rainfall prior to planting.

halosulfuron (Sandea): PHI 5d, REI 12h, Group 2. Apply 1-2 oz/A per application, up to 2 applications allowed per year. Do not exceed 2 oz/A per year. Apply uniformly with a minimum of 15 gal/A of spray. Apply to the ground on either side of the row while avoiding crop foliage. May cause significant temporary stunting and delay maturity of artichokes. Use only if you believe the utility outweighs the potential injury. Can also be applied in row middle, avoiding contact with plastic if planted in plastic. If targeting nutsedge, apply with the plants are in the 3- to 5-leaf stage. Weed control may be reduced without the use of a surfactant.

paraquat (Gramoxone SL 2.0*)REI 12h-24h, Group 22. Apply 1.7-2.7 pts/A per application, up to 3 applications allowed per year, a minimum of 7 days apart. Do not exceed 5.3 pts/A per year. Apply between rows as a directed shielded spray after crop establishment, when weeds are less than 6” tall in 20-100 gal/A of spray. May be fatal if swallowed or inhaled. Applicators must complete an EPA-approved paraquat training listed on the following website https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training...(link is external). The training must be completed a minimum of every three years.

pelargonic acid (Scythe)PHI 1d, REI 12h, Group 0. Apply a 3-10% solution (3-10 gallons per 100 gallons of spray). Apply in 75-200 gal/A of spray. Can use before planting, or as a directed and shielded spray during crop growth. Avoid contact with foliage or crop damage may occur. Spray to wet, but do not allow runoff of spray solution.

sethoxydim (Poast)PHI 7d, REI 12h, Group 1. Apply up to 2.5 pt/A per application, multiple applications are allowed, a minimum of 14 days between applications. Do not exceed 5 pts/A per year. Apply to actively growing grasses. Use with crop oil concentrate (2 pt/A) or methylated seed oil (1.5 pt/A). Note that crop oil can cause injury under hot and humid conditions. Can also be used as a spot-spray by mixing 1-1.5% (1.3-1.9 oz/gal) Poast and 1% v:v crop oil concentrate (1.3 oz/gal). Spray to wet, but do not allow runoff of spray solution.