Blueberry Plantation Design
Considerable thought should be given toward plantation design as it represents the major expense in establishing blueberries. In the past, fields were often planted at within-row spacings of 5 feet, with 10 feet between rows (870 plants/acre), to facilitate cross-cultivation and ease of hand harvesting. More recently, with increasing costs of plantation maintenance and the need to increase earlier returns, growers have been reducing within-row spacings to 2 to 4 feet while maintaining row spacing at 10 to 12 feet. Another advantage to growing blueberries in this hedgerow design is that the fields are better adapted to mechanical harvesting. With fewer gaps between the plants within the rows, the catcher plates on the picking unit will stay closed longer, thus reducing the number of berries that will fall through to the ground.
Research on optimum within-row spacing for cultivars has not been done in the Pacific Northwest. Plants set at 2 feet within the row may increase early returns of the planting, but plants may become too crowded when mature, leading to decreased productivity.
More vigorous cultivars should be planted farther apart within the row. Highly vigorous, spreading cultivars include Berkeley, Jersey, Bluejay, and Darrow. For these cultivars, a spacing of 4 to 5 feet by 10 feet (871 to 1,089 plants/acre) should be appropriate. Less vigorous, more upright cultivars such Duke, Earliblue, Patriot, Spartan, Blueray, Bluecrop, 1613-A, and Elliott should be planted 3 to 4 feet apart (with 10 foot row spacings this results in 1,089 to 1,452 plants/acre).
For mechanically harvested fields, there is a trend towards within-row spacings of 3 feet in addition to annual pruning to keep the base of the row relatively narrow, and 10 feet row spacings for machine harvesters. For fields that will be hand picked, row spacings of 8 to 9 feet make optimum use of the land, although 10 feet may still be preferred to simplify cultural practices.
Orient rows in a north to south direction to optimize sun exposure. However, if there is enough slope to warrant concern for safe tractor operation, orient rows up and down the hill. In windy areas, align the row parallel with the prevailing winds. For mechanically harvested fields, allow 25 to 30 feet at the ends of the rows to serve as a headland in which to turn around. Rows generally extend for 400 feet before a 15 to 20 foot row break is built to allow for easy unloading of harvesters and other machinery.
Some growers have found an advantage to trellising fields that are machine harvested. Use of short posts (machine must fit over them) and wire can keep branches heavily laden with fruit narrow enough to fit the “throat” of the machine harvester.
Cross-pollination of highbush blueberries leads to greater fruit set and an increase in seed number, which results in larger and earlier-ripening berries. Therefore, at least two cultivars of blueberries should be planted. Ten rows of one cultivar alternated with 10 rows of a different cultivar should ensure good cross-pollination. Highbush blueberry cul-tivars overlap enough in time of bloom to be effective pollinators for any other cultivar.
Nursery growers in the Northwest offer four different ages of bareroot planting stock, as well as container stock. Rooted hardwood cuttings, 3 to 6 inches long, are the smallest and least expensive. They should not be set out into the field, however, but rather lined out in nursery beds for one year where they can receive careful watering and fertilization.
One-year-old, field-ready plants are generally 7 to 12 inches tall and can be easily hand or machine transplanted. They are susceptible to cultural mishandling, such as lack of water or fertilizer burn.
Two-year-old plants, 12 to 18 inches tall, with a quart-sized root system are the preferred planting stock as they are considerably more hardy when planted directly into the field. Both one- and two-year-old stock will come into production 3 years after planting.
Three-year-old stock, 18 to 30 inches tall, is available for growers interested in a crop 2 years after planting. Container stock, 18 to 30 inches tall, is available, but the expense and large root ball size generally precludes its use in planting large fields.
Disease-free planting stock
Use disease-free planting stock when establishing the planting. Sort nursery stock and do not plant anything with obvious disease problems. Do not hesitate to ask the nursery operator if the plants were propagated from virus-tested mother plants.
Generally, most bareroot stock blueberry fields are established in the late winter (March through mid-April) in areas west of the Cascades. Setting out dormant plants during this period, when the weather is still cool and soil moisture levels are optimum, ensures vigorous plant growth when warm temperatures arrive in May.
Fields may also be established in the fall with bareroot stock which is generally not available until after mid-October. Early fall rains can, however, interfere with field work. Fall planting in Idaho is discouraged as young plants may heave out of the ground.
Container stock can be planted all year long, although the months of September and October are preferred, as root growth is promoted by the cooler soil temperatures. The principal disadvantage to container stock is that it is heavy and awkward to transport.
A 2 inch deep layer of sawdust centered over the rows is often incorporated (tilled) into the top 6 to 8 inches of soil prior to planting. Blueberry plants should be set at the depth they were planted in the nursery or up to one-half inch deeper. Spread the root system and firm backfill soil to maximize root-soil contact. Be sure to break root ball apart if plants were grown in containers; they may be pot-bound. Irrigate with 1 inch of water, if available, immediately after planting. Remove some of the wood at planting (see Blueberry Pruning).
Mulching the soil surface of a new planting is generally advisable to ensure that young root systems do not dry out. A 2 inch layer of sawdust, 36 inches wide, centered over the row, will inhibit the germination of annual weed seeds but not seeds of deeply rooted perennials. As blueberries are poor competitors, do not allow weed or cover crop plant growth within 2 to 3 feet of the base of the young plant within the first 2 to 3 years.
For mechanically harvested fields, planting onto slightly raised beds may be beneficial. Beds shaped 8 inches high and 12 to 18 inches wide at the top will place the catcher plates lower down on the plants where the crown is narrower. As the catcher plates will not have to open as wide, there will be less fruit loss.
Raised bed plantings will dry out more quickly, so care should be taken to ensure that the plants’ irrigation needs are met. Note that, in well-drained soils, plants need not be set on raised beds for machine harvested fields if plants are pruned to maintain narrow crowns (see Blueberry Pruning).
Newly set blueberry plants may be fertilized 3 to 4 weeks after planting (see Nutrition). Careful attention to irrigation and pest management is essential (see relevant sections).
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order