Ask anyone about growing blueberries and most likely you will hear that blueberries prefer acidic, well-drained soils. Beyond that, nobody seems to know much else.
There are many decisions to make before being able to harvest blueberries. For instance, it’s important to consider plant variety, plant spacing, first-season care, fertilizing, pruning, common pests and harvesting.
John Padua of Cobble Creek Nursery in Monkton, Vermont, has been growing and selling blueberry bushes for the past 40 years. He said he learned through trial and error what he considers to be best practices for growing blueberries. There are two common types of blueberries: lowbush and highbush. Lowbush tend to be bushes that grow wild, and highbush varieties are cultivated.
Tip No. 1: know your zone. Padua’s best advice when picking a variety of blueberry is to go to local pick-your-own farms, and see what is growing there. He also encourages first-time blueberry growers to contact their local agricultural extension service for recommendations.
In Monkton, he favors Northland, Patriot, Blue Crop, Berkeley and Elliot, a late bloomer, as they all do well in zone 4, a zone with shorter growing seasons, with a last frost around June 1 and a first frost in early October. The minimum temperature for this zone is -20 degrees Fahrenheit.
Also, he advises planting more than one variety. Some varieties require cross-pollination; some do not. To be safe, plant a few varieties that flower at the same time. Different varieties produce different sizes and degrees of sweetness of berries. Some come in late; some are early. A wide variety of plants will give a longer season of harvesting. As an aside, bumblebees are especially good pollinators for blueberries are as small as the bees that crawl inside the flower. Honey bees are less effective, as their tongues are not long enough to reach the nectar; therefore they tend to not visit the bushes. They rely on carpenter bees to chew a hole in the side of the flower, so that they can reach the nectar.
Padua’s first recommendation is to test the soil. The ideal soil pH for blueberries is 4.5 to 5.5. Analysis of the soil will help growers determine nutrient content, and other characteristics like acidity and pH levels.
Many agricultural extensions will test soil at no cost, but soil testing kits are also available at hardware stores and at local agricultural testing labs. Commonly, pine needles are used to compost around blueberries, as they add acidity to the soil. Drainage is also important. Blueberries require well-drained soil.
First-season plant care
Padua plants his 12- to 18-inch bare-root blueberries in 2-gallon pots and covers them with his own soil mix made up of a combination of bark, peat moss and composted peanut hulls. He does this in the spring and, over the course of the year, he moves them to 5-gallon pots.
When flower buds appear during the first season, he pinches and rolls the buds off because, he said, “You do not want the plants to fruit in that first year.” He also prunes stems with several buds. Blueberries need a full year to establish themselves. He fertilizes them lightly about a month after planting with a balanced fertilizer. During this first year, the plant needs to develop its branches. Tall shoots should also be pinched or pruned in June and July.
If a grower decides to plant directly in the ground, it is recommended that growers dig a large, but not deep, planting hole. Blueberry bushes have extremely fine root systems. They do not tend to grow downward but spread along the surface, rarely going down more than 6 to 8 inches deep.
Backfill with a 1:1 blend of soil and organic matter. If the soil tests correct for pH and you have proper drainage, minimal composting will be necessary. Well-rotted sawdust works well. Fresh sawdust robs roots of nitrogen, so typically it is not used. Peat moss works well but is expensive and must be moistened before use. Dry peat moss sucks moisture away from roots. Do not put fertilizer in the planting hole – not even fish fertilizer – because roots burn easily. Set plants at the same depth as at the nursery, and water them thoroughly. At planting time, prune only broken branches or branches heading in the wrong direction; plants will take a year to catch up from heavier pruning. Padua moves his blueberries to the blueberry patch after their second season in the pots. Whether you start them in the ground or move them there after two years in pots, it is critical to once again test your soil and to plant them in a well-drained sandy soil. They do not do well in clay or a hardpan that holds lots of water. They need full sun to grow and for the berries to ripen evenly. Blueberries do well when planted on slopes, as the slope can provide a windbreak, and planting them above low areas protects them from frost.
Depending on the variety, Padua plants blueberries 6 to 8 feet apart. Depending on how they are pruned, bushes can be tall or wide or both. This spacing will provide room for pruning and picking. He leaves 8 to 12 feet between rows, so he can run equipment between plants without knocking off any fruit. This spacing allows for approximately 700 plants per acre.
Although a blueberry bush might be 50 years old, most branches will be much younger – a result of pruning. Padua explained that pruning helps with fruit production, so it’s worth the time and effort. In the first three years, growers want to encourage root growth rather than berry production. This means removing broken and woody branches, weak-looking growth and most flowers. Encourage growth on the bottom of the plant to increase plant size.
Maine Organic Farmers and Garden ers Association (MOFGA) recommended: “In years four and beyond, a mature bush should have six to 12 canes ranging from one to 6 years old coming up from the ground. Remove weak, fruiting shoots and anything in excess of 12 upright canes. No individual cane should be more than 6 years old, since older canes are big, tall and mostly vegetative with very small fruit. Canes about 3 to 6 years old are most productive and have the best fruit.” A weak shoot tends to be under 6 inches long and has few or no fruit buds.
Pruning should be done when the plant is dormant, which tends to be in March. However, blueberry bushes can be pruned as early as the first of the year.
Care and maintenance
Once planted, apply a 4- to 6-inch layer of mulch around the plant base to help conserve moisture and reduce weeds. Apply a new layer of mulch when the old layer begins to break down. To prepare blueberry bushes for winter, extra mulch should be applied.
Three to four weeks after planting, apply about 2 ounces of a balanced fertilizer or 1 ounce of ammonium sulfate around each plant. There are organic equivalents for these fertilizers such as blood meal or composted manure. Spread the fertilizer in a 15- to 18-inch circle around the base of the plant. The University of Maine Cooperative Extension recommends splitting the application, applying it once in early spring and the other half about four to six weeks later. Blueberry plants do not tend to need much fertilizing; however, they do need watering. A blueberry plant needs 1 to 2 inches of water per week during the growing season. Drip irrigation works best, but sprinklers can also be used.
Weeds: MOFGA is clear that no herbicides are OMRI-approved (Organic Materials Review Institute) for blueberries yet, so they recommend mulching and vigilant hand weeding. Knowing that hand weeding is expensive and time consuming, the University of Maine’s Cooperative Extension recommends using careful, responsible use of glyphosate (trade name: Roundup and now marketed as Touchdown). Following all application instructions is important so that no damage is done to the blueberry bush.
Critters: Most birds love ripe blueberries as do bears and deer. Netting is the best way to protect berries from birds, but it can be expensive, and individual nets for each bush make picking the fruit onerous. Sound and motion deterrents tend to work for only a few days, as the birds and beasts become accustomed to them. The most effective deterrent that MOFGA has seen for birds is when a farmer attached 3/8-inch thick Mylar tape, silver on one side and red on the other, on row end posts. He stretched the tape a few inches over the bushes and twisted it in several places. The tape makes a noise when the wind blows that frightens birds. Dogs are the best deterrent for deer and bear. (read page 32 for more) .
Fungus, disease and bugs
There is no perfect fix for any of these problems, but there are organic and non-organic short-term solutions. Talk to growers to see what they are doing. The biggest pests to look for are:
Mummy berry, a fungus that overwinters and appears in early spring. A suggested remedy is to remove blighted branches, leaves and fruits.
Witch’s broom, a rust fungus. This rubbery growth occurs on branches and on the crown of the plant. A suggested remedy is to remove blighted branches and avoid planting near balsam firs, which also have the fungus.
Blueberry maggot: This fruit fly lays eggs in the berry, which causes the berry to fall on itself. Insecticides help control this pest and even a few that are listed for use in organic production. Read about this, as there are many options and all need to be well timed just before the fruit appears.
Japanese beetle: These beetles feed on leaves and the fruit once it ripens. Suggested remedies include picking them and dropping them in a bucket of soapy water, and using traps like Bag-a-Bug, placing them 100 feet from the berries as they use an attractant to lure beetles from quite a distance. Placing the trap in the berries will attract more beetles to your blueberry patch. Voles: Mow grass between mulching.
The reward comes at harvest time. Fruit should begin to ripen in mid- to late July and continue for several weeks. Pick berries 1-2 days after they turn blue for peak ripeness. When choosing varieties to plant, know that there are early, mid- and late-season varieties. If planned correctly, there is no reason to limit the harvest season to two weeks!