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Blueberry Site Selection

Carefully selecting the potential site for a blueberry plantation is one of the most important decisions a small fruit grower can make. If possible, select a piece of ground with a slight slope to facilitate both air and water drainage. Sloping ground will ensure adequate air movement around the plants all year long.

At the base of the slope, clear thick brush or thin stands of trees in order to allow cold air to drain away. During the spring bloom period of late March through April, air movement is crucial to reducing the chances of spring frost injury. Lower elevation areas in the field are often the first to show blos-som damage.

Good air circulation will also play a key role in disease control during the bloom-through-harvest period. Without good air movement, incidence of fruit rot due to gray mold (Botrytis sp.) or mummy berry (Monilinia vaccinii-corymbosi) and frost injury may increase. In cooler climate regions of the Pacific Northwest, or at higher elevations, topographic orientation should be considered. Southern exposures can be 5 to 8 F warmer during the spring and fall, thus encouraging earlier bud development (and potential for spring frost injury) and earlier berry ripening.

Slope should also be considered if the field is to be mechanically harvested. The newest over-the-row harvesters can travel across steep side slopes because they have automatic leveling. However, excessive slope will interfere with the operation of the catcher plates on the picking unit, resulting in fruit loss.

If the rows are to be orientated up and down the slope, slopes of greater than 10 percent (1 foot rise for every 10 feet) should be avoided as berries will tend to roll to the back end of the picking unit and will not be collected properly.

In areas prone to the effects of cold sweeping winds during the winter, the use of windbreaks is recommended. Windbreaks should be porous so as to slow wind speed by approximately 50 percent.

Besides preventing winter desiccation, well-managed windbreaks will reduce excessive water loss from the soil in the summer, and will help improve pollination during bloom as bees will be more prone to exit their hives. A good discussion of windbreak species and their installation and maintenance can be found in PNW 5, Trees Against the Wind, available from Oregon State Extension Service (see Bibliography).

Soil drainage

The best blueberry soil type is one in which winter precipitation drains through completely, yet sufficient moisture is held during the dry summer months to support good plant growth. Silt and sandy loam soils are best, as they generally have good water infiltration capacities, moderate water-holding capacities, and good drainage. The fine, fibrous root system found on the plants requires that plantings be located in open, porous soil. The delicate roots simply cannot penetrate a heavy, compact soil.

Soil organic matter levels should be at least 3 percent. Avoid heavy, clay soil types as they do not allow good root distribution and contribute to poor water infiltration rates and drainage capacity. Flooded soils reduce blueberry plant growth by reducing gas exchange rates between the soil and the atmosphere. When all of the soil pore spaces are filled with water, microorganisms consume soil oxygen that would otherwise have been consumed by the blueberry roots.

In addition, water-logged soil can lead to accumulation of reduced compounds such as sulfide and ferrous oxides which can be deleterious to blueberry plant growth. Phytophthora root rot of blueberries can also occur under poorly drained conditions. Highbush blueberries can tolerate a maximum of 4 days of flooding during the winter, and 1 day in the spring or fall.

The best time to assess the drainage capacity of the soil type selected is in the winter after a heavy rainfall. Ideally, no standing water will form puddles in the field. Water which does not seep through the soil profile after 24 hours indicates very impermeable soil texture.

The best method of determining the soil texture is to consult the U.S. Soil Conservation Service Soil Survey booklet for the county in which your field is located. After you have identified the soil series in question, consult the thorough description of the depth and color of the soil profile. Brown or reddish-brown soil color is indicative of good drainage, while yellow or gray mottled colors signal poor drainage.

The best blueberry fields are those that have a water table at least 14 to 24 inches below the soil surface. Agricultural drain tile can be installed in fields with problem drainage spots. The feasibility of installing a drain tile network on ground that suffers from impermeable soil texture types is questionable. Growers are urged to consult with an agricultural engineer, soil scientist, or drainage contractor in cases where poor drainage is of concern. Plastic drain tile is usually set 3 to 5 feet below the soil surface and must be installed prior to planting a field because the drain lines will usually not parallel plant rows. Besides optimizing plant growth, installing drain tile will increase the trafficability of a piece of ground, which is particularly important in the spring.

To overcome problems with high water tables, growers have tried elevating the plants within the rows on mounds or raised beds. Beds should be about 8 inches high and 48 inches wide. If the field is to be mechanically harvested, do not have high raised beds (greater than 8 to 10 inches high) or problems will arise with adjusting the height of the catcher plates so that they are not dragging in the soil.

Generally, mineral soils are used for blueberry production in the Pacific Northwest. Muck soils (20 percent to 50 percent organic matter) and peat soils (more than 50 percent organic matter), which are found in the northwest portions of Washington State and southwest British Columbia, will limit blueberry production. These soil types remain cold and wet during the spring, thus slowing normal plant development. On very light sandy soils, greater attention will be needed to meet the plant’s moisture requirements during the summer months.

Irrigation water

Supplemental irrigation is nearly always essential for successful production. A source of unchlorinated water with a low salt content (<0.1%) and low ph (<6.0) is most desirable (see Water Management for Blueberry).

Previous cropping history

Wooded areas that are destined for blueberry production need special attention. Stumps and root pieces should be pushed or dragged off the planting site. If this material is burned as it lays, the alkaline minerals released from the burn piles will raise the soil pH well above 7.0, thus having a negative impact on future plant growth.

Determine the presence of residual pesticides from previous crops grown. If farming records are not available, growers may compare the germination and growth of oat seedlings in clean soil with soil from the prospective planting site. Place soil in paper milk cartons which have drain holes. Water the pots and then place them in a warm sunny location. Within 3 weeks, potential pesticide injury symptoms will be evident. Check with your local county Extension agent for possible causes of symptoms.

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