Blueberries for Home Garden
|Written by:||Kevin Schooley - Horticultural Crops Advisor/OMAFRA; Leslie Huffman - Weed Management Advisor/OMAFRA|
Table of Contents
Blueberry bushes are long-lived plants with a lifespan similar to fruit trees. The berries are versatile and can be enjoyed fresh, used in desserts or stored by canning or freezing. In addition, the plants provide ornamental value with their delicate white blossoms in the spring and fiery foliage in the autumn.
Highbush blueberries grow and survive best in the milder regions of Ontario. Midwinter temperatures of -29°C to 32°C can severely injure or kill both flower buds and young branches. In marginal areas for highbush blueberry cultivation, deep snowcover throughout the winter will help insulate the plants and reduce the extent of winter injury. The parts of the bushes which are protected by snow may produce a crop. Different blueberry cultivars also vary widely in their degree of winter hardiness. Lowbush or half-high blueberries (see section on Cultivars) may survive in colder regions which receive adequate and reliable snowfall.
Figure 1. Bright foliage colour in autumn adds to the ornamental value of highbush blueberries
Blueberries prefer full sun, although the plants will tolerate partial shade. As shade increases, the bushes produce fewer blossoms and fruit production declines.
Blueberries require acidic, well drained, loose soils with a high organic matter content. Good drainage is important because the very fine root system needs adequate aeration. The roots of blueberries will suffocate if they remain in water-saturated soil for even a few days. Water tables should always remain at least 30 cm below the soil surface. Avoid low-lying locations since they may be poorly drained and prone to frost.
The pH of the soil is critical for blueberry growth. Blueberries grow best at a pH of 4.2 to 5.0, although they may tolerate a higher pH up to 5.5. A soil test can determine the soil pH. If the soil pH tests between 5.0 and 6.5, sulphur applications will acidify the soil and reduce the pH. If the soil pH tests higher than 6.5. sulphur will not adequately reduce the pH and the soil is not suitable for blueberry production.
Since blueberry bushes will live and produce berries for many years, take special care to adequately select and prepare the soil before planting blueberries. Prepare the site one full year prior to planting.
Organic matter improves soil aeration and drainage while retaining moisture and nutrients. Blueberries establish better, grow more vigorously and yield more fruit if organic matter is incorporated into the soil prior to planting. Acid peat moss is the preferred source of organic matter. Work 10 to 15 cm of acid peat thoroughly into the top 15 to 20 cm of soil. Acid peat will also help lower the soil pH. Other sources of organic matter include, well-rotted manure, straw, compost, or aged sawdust.
If the soil pH tests between 5.0 and 6.5 on a well-drained, sand to sandy loam soil, add sulphur to lower the pH to between 4.5 and 5.0. Apply sulphur the year before planting and thoroughly mix it into the top 20 cm of soil. The amount of sulphur required to lower the pH differs for each soil. As a guide for sandy loam soils, add 75 to 100 g/m2 for each full point the soil registers above 4.5. (For example, if the pH is 6.5, add 150 to 200 g/m2.) For sandier soils, use 35 to 50 g/m2. Since sulphur takes several months to reduce the pH, wait a few months before re-testing to determine if more sulphur is required.
Soils which have a pH above 6.5 ,poor drainage, or a clay texture are not suitable for blueberry production. A raised bed could overcome problems such as drainage. To create a raised bed, replace some of the soil with 8 cm of coarse material such as gravel or crushed stone to provide good drainage. On top of this coarse material add a minimum of 30 cm of a mixture of half sandy topsoil and half acid peat. Use logs, stone, bricks, etc. to contain the soil mixture. Prior to planting, check to ensure the pH of the bed is 4.2 to 5.0.
Eradicate all perennial weeds such as quackgrass, bindweed and vetch in the year prior to planting. Cultivate or pull weeds before they begin to produce seeds.
Before planting blueberries, incorporate phosphorus and potassium into the soil according to soil test results.
Use strong, dormant two or three-year-old plants which are free from viruses and diseases. Obtain plants as close to planting time as possible. If necessary, plants will store for short periods in a refrigerator or other cool place. Sprinkle dry roots with water and place bare-rooted plants in plastic bags before storing. Do not leave roots soaking in water or they will die. If plants must be held for more than one or two weeks, dig a trench in well-drained soil, set plants in the trench, and cover roots with soil. Potted plants should be stored in a cool place. Water the plants if the soil moisture is low.
Set highbush blueberry plants 1.0 to 1.5 m apart within the rows. The distance between rows will vary from 1.5 to 3.0 m apart, depending on available space, aisle width desired, and any machinery requirements. Planting rows 1.5 m apart will result in a walking aisle only; spacing rows 3 m apart will accommodate most machinery.
Plant the dormant blueberry bushes in early spring as soon as the soil can be worked. Prune any broken roots or branches and set the plants 3 to 5 cm deeper than they were grown in the nursery. Spread out the roots and cover them with soil. Firm the soil around the roots, being careful not to cause breakage. Blueberry roots are very fine and must not dry out at any time during planting. Water the bushes thoroughly after planting.
Remove blossoms as they appear during the first and second season. This helps the plants establish quickly and grow more vigorously.
Weed Control, Mulching
Blueberries have a shallow root system which is easily damaged by cultivation or deep hoeing. Mulching the plants with sawdust, wood shavings or clean straw will aid in weed control and help conserve moisture. Make sure the mulch is moist before applying it. Spread the mulch in a band 60 cm wide, with 30 cm on each side of the plant row. Add mulch to a depth of 5 to 10 cm. Grass, such as creeping red fescue, can be planted and allowed to grow between the mulched bands if the sod is mowed regularly.
As the plants grow larger, gradually widen the mulched area to 60 cm on each side of the bushes. Add mulching material as required to maintain a mulch depth of 5 to 10 cm.
Immediately remove any weeds which grow through the mulch since broadleaf weeds and grasses compete strongly with blueberries for moisture and nutrients. Never allow weeds to produce seed.
Use fertilizer mixtures which supply nitrogen as ammonium sulphate (when the soil pH is above 5.0) or urea (when the soil pH is below 5.0). Supply potassium in the form of potassium sulphate or sul-po-mag. Avoid muriate of potash, since it contains chloride which can be toxic to blueberries.
Potassium and phosphorus should be applied according to soil test results. In the year following planting, apply 14 to 18 g of nitrogen per highbush blueberry plant. in addition to the potassium and phosphorus. (This rate of nitrogen would be contained in 140 to 180 g of a 10-10-10 fertilizer.) Increase the rate of nitrogen each year by 4 to 6 g per bush until a total of 36 to 48 g per bush is applied. Apply the fertilizer just prior to budbreak. On sandy soils, apply two-thirds of the nitrogen at budbreak and the other one-third at petal fall. Distribute all fertilizer evenly under the bushes to just beyond the spread of the branches.
Check the soil pH every year or two, especially if plant growth is poor. Iron deficiency is common when the soil pH is too high. Normally, young leaves are a lighter green than older leaves and often have a slight reddish tint. When deficient in iron, young leaves become pale yellow and stunted, and plant growth is poor. If iron deficiency occurs, make every effort to correct the soil pH. Water or lightly rake sulphur into the soil or mulch according to the pH. To avoid possible burning of the blueberry roots, delay the sulphur application until one month after applying the fertilizer. Foliar sprays of iron chelate can temporarily correct an iron deficiency. but annual sprays may be necessary.
Figure 2. Highbush blueberry bushes in foreground are showing iron deficiency due to improper soil pH (soil pH above 5.5). The condition of bushes in background gradually improves as the soil pH becomes more acidic and suitable.
Blueberries have shallow roots and require a uniform and adequate moisture supply throughout the growing season. A constant moisture supply ensures good plant growth and fruit production. Mulch reduces moisture fluctuations and significantly improves moisture conservation. As a guide, blueberries require at least 25 mm of water per week until early September. Watering is essential whenever rainfall does not supply this amount. To encourage the plants to harden off before winter, do not water after early-to mid-September unless the soil becomes very dry. Avoid overwatering the plants or the roots will be injured and killed.
Blueberries respond well to trickle or drip irrigation. The system slowly adds small amounts of water each day directly to the soil around the base of each plant. Fertilizer can also be applied through the irrigation system. Both automated and manually operated systems are available. Several manufacturers sell trickle irrigation which can be used in blueberries.
Berries develop in clusters of 5 to 10 berries and ripen over a period of 4 to 6 weeks. Blueberries are often harvested too early. After the berries turn completely blue, leave them on the bushes for 3 to 7 days to develop their full flavor and sugar content. To free both hands for picking, attach a basket with a belt at waist level. Gently roll the berries between the thumb and forefinger, removing fully ripe berries and leaving unripe berries for the next picking. Berries that shrivel or split have probably remained on the bush too long. Harvested berries should be removed immediately from the sun and can be stored for a week or more in the refrigerator if kept dry.
Birds find blueberry fruit very attractive and can eat the entire crop of a small planting if it is not protected. To prevent losses, cover individual bushes or the entire planting with netting supported by a light framework, put up the netting just before the berries turn blue. The netting should not shade the plants or they will not flower well the following year. Remove the netting after harvest to avoid damage from winter ice and snow.
Prune highbush blueberries while the plants are dormant in late winter or early spring after the threat of extremely cold temperatures has passed. Avoid pruning too early in the winter. Pruning stimulates the plants, causing them to lose some dormancy and increasing their susceptibility to winter injury.
Young bushes require little pruning in the first three years. Remove any damaged or diseased portions of branches and any weak, spindly growth at the base of the plant. Encourage vigorous, upright growth.
Older bushes require regular annual pruning to produce high yields of large fruit. Fruit will develop on strong one-year-old wood with good exposure to sunlight. First, prune out any dead, broken, injured or diseased branches. Next, remove any canes that are spindly or growing near or along the ground. Finally, cut off at ground level canes low in vigour, canes older than 5 years, and any canes larger than 5 cm in diameter. Keep 4 to 6 vigorous mature canes per bush, plus any strong new shoots. If winter injury is not severe, select 1 or 2 of the new shoots to keep and remove the remaining young shoots. These new shoots will eventually replace the older canes. When pruning, cut out entire shoots at the base; do not prune tips off the remaining branches.
Different blueberry cultivars vary in their ability to withstand winter cold; however, cultural practices will also influence winter hardiness. Any conditions which stimulate growth of the plants late in the season will increase their susceptibility to winter injury. Apply moderate rates of nitrogen early in the spring, avoiding applications beyond June. Avoid watering late in the fall, unless the soil is excessively dry. Do not prune in late fall to early winter or plants will lose some of their winter dormancy.
Young branches of blueberry plants are attractive to rabbits. Most of the damage from rabbits occurs during the winter when other food is scarce. If rabbits are present, it may be necessary to enclose the sides of the planting with a fine chicken-wire fence or netting. Make sure the sides are high enough so the rabbits cannot jump over the fence when the snow if fairly deep.
If grass is planted between the rows, mow the sod short late in the fall to discourage mice from nesting near the blueberries. If mice arc abundant, reduce populations by placing poisoned bait into bait stations in areas frequented by mice. Plastic pipe cut into 20 cm lengths or tin cans with both ends removed make suitable bait stations by protecting the poisoned bait from adverse weather, birds and domestic animals.
Figure 3. A well-managed highbush blueberry planting. Note trickle irrigation system, frame for supporting protective bird netting, and addition of mulch.
Blueberry plants will remain productive for 20 years or more if growing conditions are good and if plants are healthy and properly pruned. Highbush blueberry plants should produce about 225 g of berries per bush in the third year, and about 450 to 900 g per bush in the fourth year. Yields should increase until the plants are 6 to 8 years old. A mature bush should produce 2.5 to 3.5 kg of berries, although higher yields are possible.
Plant several different blueberry cultivars for cross- pollination, to extend the harvest season. and to determine which cultivars perform best under the conditions provided.
Midseason, productive. Plants are vigorous, upright, open and hardy. Fruit clusters are loose; berries are light blue, large in size, very firm, with a good, slightly tart flavor. Fall leaf color is a medium dark red.
Midseason, productive. Plants are vigorous, erect and fairly hardy. Fruit clusters are small and tight; berries are medium to dark blue, very large, firm, aromatic, with good flavor. Blossoms are reddish and fall leaf color is a medium dark red.
Late midseason, productive. Plants are large, bushy, upright and hardy. Fruit clusters are loose; berries are medium blue, medium sized, firm, with fair flavor, lacking aroma. Fall leaf color is a light, bright red.
Early midseason, very productive. Plants are slightly short, bushy, moderately spreading, and very hardy. Fruit clusters are long and loose; berries are medium to dark blue, medium-small, moderately firm, with good flavor. Very good ornamental value.
Early midseason, productive. Plants are small to medium sized, vigorous, upright and very hardy. Fruit clusters are tight; berries are medium blue, very large, slightly flattened, firm, with very good flavor. Good ornamental value.
The colder regions of Ontario are only marginally suitable for high-bush blueberries. Lowbush blueberries or half-high blueberries may survive better, especially if snow insulates the plants throughout the winter.
Lowbush blueberries are low, spreading, plants that often grow wild in northern regions of Ontario. Lowbush blueberries produce small to medium sized, flavorful berries. Cultivated low-bush blueberry planting stock is available. Lowbush blueberries should be planted 50 cm apart in rows 100-150 cm apart. Plant lowbush blueberry crowns 3 to 5 cm below the soil surface to promote spreading of the plants by underground rhizomes.
Half-high blueberries resulted from crossing lowbush and highbush blueberries together. Northblue is a vigorous half-high blueberry that reaches 50 to 75 cm in height and is hardy to -30° C. Northblue produces dark blue, large, firm berries. St. Cloud is a large half-high (100-120 cm) with an upright growth habit. Fruit is medium blue, large and slightly flattened. Northcountry is a smaller half-high (45 to 60 cm) that produces sweet, mild, sky-blue blueberries. Plant half-high blueberries 60 to 75 cm apart.
Insects and diseases seldom cause problems in most plantings.
Cherry and Cranberry Fruitworm moths lay their eggs on newly set blueberries just after bloom. Cherry fruitworm larvae bore into the berries and tunnel into adjacent berries, lining the junctions with silk. Cranberry fruitworm larvae burrow into the berries near the stem end and feed inside the berry. Infested berries shrivel and turn blue prematurely. The larvae web together infested and uninfested fruit with stands of silk and pellets of frass. To control both fruitworms, remove and burn infested berries promptly to destroy the larvae inside before they exit and pupate. Insecticide sprays are also effective in preventing infestations if applied before the larvae bore into the fruit. Apply a recommended domestic insecticide (such as malathion or carbaryl) just after petal fall and repeat 10 days later.
Figure 4. Reddish brown foliage on upper portion of highbush blueberry bush is caused by cankers girdling the stems. The injured stems should be pruned out immediately and burned.
Careful pruning will help prevent disease outbreaks. Prune out and destroy any part of the plant which is dead or dying. Examine the plants frequently for cankers which first appear as small, reddish, discolored areas on the stems. As the affected areas enlarge, the margins remain reddish and the bark in the central part turns gray and then brown. Cankers often occur close to the ground level but may occur higher on the stem. Cankers can girdle the blueberry stems in one season, causing the affected stem to die. As the stems die, the foliage turns reddish brown. If cankered stems appear, immediately cut out the affected parts 10 to 15 cm below the cankered area. Remove and burn the diseased prunings.
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