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 bud, of which the fleshy bases of the bracts 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 composite flowers 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 50º F for prolonged periods, globe artichoke is a perennial crop that is propagated vegetatively.  In perennial systems, artichokes will produce in their first year but yields will be improved thereafter.  In colder regions like New England, artichoke can be grown annually from seed.  While most if not all varieties can be grown as annuals, some varieties have been bred that reliably produce many buds in their first year after a vernalization period (see Planting section).  

Globe Artichoke Varieties
Colorado Star (A) Romanesco
Emerald Tavor (A)
Green Globe Improved Violetto
Imperial Star (A) Wonder
Imperial Star Purple (A)  
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 having 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 8-12 weeks before transplanting into 50-cell trays or 3-4” pots.  Seeds take 8-12 days to emerge. Germinate at 70-80º F, 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 45-50º F for at least ten days, although the amount of chilling required varies by variety.  Alternatively, transplanting can be timed so that transplants get their chilling time outdoors (use row cover if frost is expected).  However, this is less reliable than artificial vernalization and coolers should have ample space in spring for seedlings. 

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 plastics mulch effects on artichoke production have mixed results.  Plants need an inch of water per week, for which drip irrigation is useful. Artichoke buds should begin to form in late July.  If desired, the healthiest artichoke plants with several side shoots can be split at the end of the season 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 unclear whether the proportion of plants that survive winter would be large enough to warrant overwintering versus annual production. 

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.  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 and can be sold by weight, quart container, etc.  Secondary buds can be eaten much like larger sizes, but are often more tender with a larger proportion of the bud being 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 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 32º F, but should not be allowed to freeze.  Artichokes can last 2 weeks or longer in storage. 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.

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. 

Herbicides Used Preemergence to Weeds

pendimethalin (Prowl H2O)PHI 60 or 200 d (based on rate), REI 24h, Group 3. Must be applied at least 1 to 2 days before transplanting artichoke. Apply up to 3 pt/A so soil surface for 60 day PHI, or a higher rate of 3.1 to 8.2 pt/A can be used but requires a 200 day PHI.

Herbicides Used for Pre- and Postemergence Weed Control

oxyfluorfen (Goal 2 XL): PHI 5d, REI 48h, Group 14. Used for both pre- and postemergence weed control.  Apply 4 to 6 pt/A as a directed spray to the soil surface between the rows and at the base of artichoke plants.  Do not apply over-the-top. Contact with direct spray or drift will cause injury to artichoke fronds or severe injury to buds or flowers. Do not apply more than 6 pints of Goal 2XL per acre per season as a result of a single application or multiple applications.

Herbicides Used Postemergence to Weeds

clethodim (Select Max)PHI 5d, REI 24h, Group 1.  Will control grass weeds only. Apply to actively growing grasses.  See label for rate selection.  Multiple applications permitted of 9 to 16 oz/A per application, minimum 14-days between applications, not to exceed 64 oz/A per year.  Add 0.25% v:v nonionic surfactant (1 qt per 100 gal of spray).  Can also be used as a spot-spray by mixing 1/3-2/3% (0.44 to 0.85 oz per gallon) Select Max and 0.25% v:v nonionic surfactant (0.33 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.

paraquat (Gramoxone SL 2.0*): REI 12h, Group 22.  For use between rows after crop establishment. Apply up to 2.5 to 4 pt/A as a directed and shielded spray to emerged weeds between rows when weeds are succulent and weed growth is less than 6”. Maximum 3 applications per year, not to exceed a total of 8 pt/A per season.  Use precision directed spray application equipment adjusted to prevent spray contact with crop plants. Crop contact by the spray will cause severe injury or death. Do not exceed 30 psi nozzle pressure or spray under conditions which may cause excessive drift.

sethoxydim (Poast): PHI 7d, REI 12h, Group 1.  Controls grass weeds only.  Apply to actively growing grasses (see product label for susceptible stage).  Maximum 2.5 pt/A per application, minimum 14-days between applications.  Do not exceed 5 pt/A per year. Use with crop oil concentrate (2.0 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 to 1.9 oz per gallon) Poast and 1% v:v crop oil concentrate (1.3 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.

Disease Control

Gray Mold (Botrytis cinerea)

Botrytis is most problematic in wet conditions and as a secondary pathogen.  Infection of bracts will appear as somewhat sunken brown lesions, with characteristic gray mold sometimes developing on the inside of bracts.  Preventing insect feeding and other wounds can help mitigate gray mold.
 

Insect Control

Aphids, primarily Green Peach (Myzus persicae)

Green peach aphid overwinters 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, winged females develop and leave in search of new plants. In fall, both 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), as well as broadleaf weeds, support green peach aphid. Feeding on young tissue causes curling, wilting, stunted growth, and contamination of harvested crop. The major damage caused by this aphid is the transmission of many different 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 leaf underside is important. Add a spreader-sticker. Plant crops away from Prunus species. Spray effectiveness may vary depending upon the species present. Reflective plastic mulch may help to repel aphids. 

Tarnished Plant Bug (Lygus lineolaris)

See Lettuce for information about tarnished plant bug. In artichoke, 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 and rendering them unmarketable.

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.