VARIETIES

Green Globe grown from crown divisions or shoots is preferred. Seed under the same name is also offered by several seed companies but the Green Globe propagated from seed may be, and usually is, quite different from that grown from shoots produced by the artichoke industry in California. Artichoke plants grown from seed tend to be variable with only 60-70 percent of the plants producing marketable "chokes."

In 1991 a new hybrid globe variety, Imperial Star, became available. This variety was developed by Wayne Schrader and Keith Mayberry of the California Cooperative Extension Service. It is more uniform than previous varieties produced from seed, reportedly does not need as much vernalization as Green Globe, is thornless, and is primarily green, but has some purple tinting. The variety has shown broad climatic adaptability and is currently being grown in southern California coastal regions, and in desert areas in California and Arizona.

Possible seed sources for Imperial Star include: Keithly-Williams Seeds, Contact: Jim Christopherson or Ernie Keithly, 420 Palm Avenue, PO Box 177, Holtville, CA 92250, Phone: 760-356-5533, Fax: 760-356-2409; and: Palmer Seed Co., D., 8269 S Highway 95, Yuma, AZ 85365, Phone: 520-341-8494, Fax: 520-341-8496.

Another new variety, Emerald (D. Palmer Seed Co.), is also now available. It is adapted in California to both coastal and inland valley conditions. Based on experience at Oregon State University in 1998, Emerald was about two weeks earlier than Imperial Star, and appears to need little, if any, vernalization. Emerald buds tended to be angular in 1998, which had an exceptionally warm summer. Two other artichokes that are grown from seed are Grand Buerre and Talpiot, developed in Great Britain and Israel, respectively.

A purple globe artichoke, more tolerant to heat and cold and grown from seed, is the variety Purple Sicilian. The purple-tinted artichoke currently available in produce markets was developed and is marketed exclusively by Dole Food Co.

For trial: Northern Star, developed by Peters Seed & Research, is reported to be hardy to temperatures below 0 F without winter protection.

CLIMATIC REQUIREMENTS

Proper climatic conditions are extremely important in artichoke production. Artichokes do best in a frost-free coastal area with cool foggy summers. Under such conditions the plant receives the proper vernalization and the right climatic conditions throughout its growing period to produce compact, tender buds for an extended period.

1991 and 1992 research data from Virginia indicates that about 1300 hours of temperatures under 50 F were adequate to completely vernalize Green Globe and Imperial Star. However, after only 200 hours, over 80% of the plants of Imperial Star flowered compared to 25% for Green Globe. Grande Buerre and Talpiot did not flower even after 500 hours of chilling. As noted above, Emerald appears to require very little vernalization.

In the Willamette Valley, late summer and early fall production should be targeted due to hotter mid-summer temperatures which may result in rapid flower stalk growth and poor quality. The variety Imperial Star is reported to be tolerant to warm summer temperatures.

Care must be taken that artichokes are not exposed to temperatures below 25 F in the winter. Where this occurs, straw mulching is recommended. In the Willamette Valley it is advisable to chop off the stalks in the fall after the last harvest and to lay a mulch before the first frost occurs if the field is to be maintained over winter. At temperatures under 15 F severe loss of crowns would be expected even with mulch protection.

A hot dry climate causes artichoke buds to open quickly and destroys the tenderness of the edible parts. In the summer, irrigation may be used to keep temperatures down in the crop canopy to prevent bud opening. Cold weather also easily damages artichokes. At temperatures near or below freezing the outer skin of the bud scales ruptures, giving the bud a blistered, whitish appearance. After a few days the blistered skin turns dark; this does not impair the eating quality of the artichoke but does make it more difficult to market.

SOIL

The globe artichoke will grow on a wide range of soils, but it produces best on a deep, fertile, well-drained soil. The plant is deep rooted and should be planted on soils that afford adequate area for root development. Where coastal climatic and soil conditions are satisfactory many plantings are made on gently sloping hills. Hillside soils usually require more fertilizing and careful management of irrigation water. However, if properly done, these areas can be as productive as those that are level.

PRODUCTION FROM SEED

Artichoke seed numbers approximately 800/ounce. When artichokes are grown from seed, they can be grown as an annual in the Willamette Valley or other areas where they are not likely to survive over-winter due to freezing or flooding.

Production from seed is best when transplants are grown and set out early enough in the spring to satisfy vernalization requirements, yet after danger of frost is past. Transplants might also be properly vernalized by holding them under refrigeration for the needed time. Some researchers have used 4 weeks at 35-40 ^oF for soaked seed with questionable success, but transplants may be more responsive. The exact vernalization time for transplants is not known, and would vary with location and variety, so a 2 to 4-week exposure at about 40 F should be tested and the proper vernalization exposure done before setting transplants in the field (see also comments about vernalization in the "climatic requirements" section above).

Direct seeding may be possible if seed vernalization as suggested by researchers in Connecticut is effective. Although results are uncertain, researchers in Connecticut indicate that conditioning may be possible by pre-soaking the seed for 48 hours to soften the seedcoat, and then holding the moist seed for 4 weeks at temperatures of 35-40 F in moistened, un-shredded, sphagnum moss (to allow for adequate aeration as well as moisture). Lack of aeration will result in delayed germination and cause seed to decay.

DIRECT SEEDING

Direct seeding may be done in early May, but since the plants will have the same vernalization requirements mentioned above, only about half the plants will flower in the fall. Imperial Star may have a higher percentage of plants that flower, however. Buds will generally develop about 3 or 4 weeks later than from unvernalized transplants.

Although growers in California use low plant populations for permanent plantings--generally about 1000 plants per acre, final spacing in Oregon should be 3-4 feet apart in rows spaced 6-10 feet apart for plantings expected to be permanent, because "permanent" plantings would generally have to be renewed sooner.

When growing this crop as an annual (one season only), spacings within the row may be 2-3 feet apart, with rows 3-4 feet apart. If the planting survives to another year or more, alternate rows may be removed and used as planting stock for additional acreage.

These plant densities may result in greater competition and smaller chokes at harvest. Adjust populations according to your market's choke size requirements. Although fewer 18 and 24-count chokes may be produced at these higher densities, total production of all sizes would be expected to be greater. However, no specific data on the effect of plant density on choke size have been developed at Oregon State University.

SEEDING FOR TRANSPLANTS AND TRANSPLANTING

Sow seed in the greenhouse in to allow for adequate vernalization after transplanting to the field as noted above. Transplant seedlings 2-3 feet apart in rows 3-4 feet apart as mentioned for "direct seeding". Plants should produce chokes for harvest in September and early October. Generally, 90 to 100 days are required before flowering occurs.

PRODUCTION FROM CROWN DIVISIONS OR SIDE-SHOOTS

The normal method of propagating artichoke fields in California is from crown divisions or sideshoots. This insures that the field will be true to type. Green Globe planting stock is difficult to obtain. Arrangements must be individually made with growers in established production areas.

Care must be exercised in obtaining clean planting stock as a number of diseases are easily transmitted in this manner. The most common are Curly Dwarf and some crown and bud decay organisms.

FERTILIZER

Fertilizer applications should be made according to current soil test information. The following are general recommendations:

20-30 tons/acre of manure, if available, worked in before planting.

Nitrogen: 100-200 (N) lb/acre - Apply one-fourth before planting, and the balance when plants are established (6-8 weeks later) for first year fields. Apply 60-100 lb N/A again early each spring before buds begin to form for second-year, and older fields.

Phosphorus: 100-200 (P₂0₅) lb/acre - Broadcast and worked in before planting.

Potash: 100-200 (K₂O) lb/acre - Broadcast and worked in before planting, based on soil test.

Sulfur: 15-25 (S) lb/acre - Broadcast and worked in before planting.

IRRIGATION

Artichokes are deep rooted and when grown in the mild coastal climate, require up to 15 inches of water during the production season. This may have to be provided by some irrigation. If grown in other areas of Oregon, considerably more water may be needed. Base irrigation on local weekly evapotranspiration.

According to information from the University of California, moisture stress may cause a disorder called Black Tip. This physiological disorder (cause not known) usually damages only the exposed bracts of small axillary buds. The tips of the affected bracts become dark brown or almost black, dry, and leathery. The edible portion of the bud is not affected but the bud is rendered unmarketable. Damaged tissue may become a site for postharvest decay. In annual-seeded production, black tip appears most frequently during sunny, warm, and windy conditions that increase the growth rate and put plants under periodic moisture stress. Careful attention to soil-water relationships is important in alleviating this disorder.

Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.

USE OF GROWTH REGULATORS

Gibberellic acid (GA₃ or GA₄₊₇) foliar applications can enhance earliness by several weeks and improve uniformity of flowering. Treatment consists of two to three foliar sprays at 2-week intervals, applied at 20 ppm and 30 gallons/acre and totalling no more than 6.6 grams GA/acre. Application is usually made 5-7 weeks after transplanting, when plants are 18-25 inches in diameter. For more information see San Diego County Artichoke Production (UC-Davis).

Treating plants in four separate blocks, one at 5 weeks after transplanting, the next block at 6 weeks, the third at 7 weeks, and the final block left untreated will stagger flowering to allow for orderly harvest.

Caution: Misapplication of GA can reduce plant vigor, increase susceptibility to black tip and spider mite damage, and cause elongation of the buds. Damage may occur especially when applications are made too early, at high rates, and when excessive temperatures occur during or immediately following application. Follow the label for timing, rates, and temperature limitations. Note that the environmental conditions of western Oregon may cause artichoke response to GA to differ from that experienced in California. Start with small trials only.

HARVESTING, HANDLING, AND STORAGE

Approximate yields in California average 450 cartons, with good yields at 550 cartons/acre for established plantings. Select buds for size, compactness, and age. Harvest by cutting stem 1 to 1.5 inches below base of the bud. All buds that are of suitable size should be removed. Old stems should be removed as soon as all buds have been harvested to allow new stems to grow.

STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)

The edible bud is seldom stored; but for temporary holding a temperature of 32-33 F is recommended, with a relative humidity of 95 to 100%, to prevent wilting or drying. To maintain quality and storage life, the buds should be pre-cooled to below 40 F on the day of harvest. Large artichokes (3.5 inches in length and width) will take almost twice as long to hydrocool as small ones (about 3 inches in length and width). Water loss can be minimized by packing the buds in waxed cartons or in cartons lined with perforated film having fifty 1/4-inch holes per square foot. The holes are necessary to drain excess water from hydrocooling and to release heat and gas produced from respiration. Artichokes of good quality without decay or freezing injury will keep in good condition for 2 to 3 weeks at 32 F.

POSTHARVEST FIELD CARE

If fields are to be maintained over winter, chop and bury the above ground plant residue after harvest and after the leaves become dormant in late fall. Burying the residue is important in reducing carryover of pathogens and insect pests. Where appropriate, cover the rows with clean straw or clear plastic to shed rain and improve over-winter survival. The plastic or straw has to be removed when growth begins in spring.

PACKAGING

Chokes are commonly packaged in cartons and boxes, 7 inches deep, by count and loose pack, 20-25 pounds net weight.

Size classifications are:

• 18 = Bud diameter over 4.5 inches, 18 buds per carton
• 24 = 4.0-4.5 inches
• 36 = 3.5-4.0 inches
• 48 = 3.0-3.5 inches
• 60 = 2.75-3.0 inches
• Small loose = 1.0-2.75 inches

PEST CONTROL FOR GLOBE ARTICHOKES

Note that the state of Oregon requires reporting of agricultural pesticide use through its Pesticide Use Reporting System.

USE PESTICIDES SAFELY!

Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.

Read the pesticide label--even if you've used the pesticide before. Follow closely the instructions on the label (and any other directions you have).

Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.

WEED CONTROL

The Pacific Northwest Weed Control Handbook has no control entries for new plantings of this crop. Herbicides registered, but not evaluated by University personnel in the Pacific Northwest, include Devrinol, Karmex, Kerb, Poast, Roundup, and Touchdown. Consult labels for rates, restrictions, and weeds controlled.

Cultivate as often as necessary when weeds are small. Proper cultivation, field selection and rotations can reduce or eliminate the need for chemical weed control.

For weed control in established plantings, see PNW Weed Management Handbook - Vegetables.

DISEASE CONTROL

The Pacific Northwest Disease Control Handbook has no control entries for this crop. Ridomil is registered but has not been evaluated in the Pacific Northwest. Consult label.

Proper rotations, field selection, sanitation, spacings, fertilizer and irrigation practices can reduce the risk of many diseases. Fields can be tested for presence of harmful nematodes. Using seed from reputable seed sources reduces risk from seedborne diseases.