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National Gardening Association Beat the Blueberry Blues

By Robert E. Gough

For 20 years I've been helping people take care of highbush blueberries in their backyards or in commercial plantings. The scenario is nearly always the same. Young bushes are planted with great care and then, after the novelty has worn off, are left to struggle, overgrown, among the weeds. But with proper attention to good soil management and proper pruning, blueberries shed their mystery and the bushes bear bountifully for generations.

Good soil management is most crucial. Without it, the bush will produce little to prune. Blueberries don't compete well for water and nutrients and require especially good soil aeration. You can practice shallow cultivation (less than two inches deep!) regularly during the growing season to aerate the soil and to keep heavy weed growth down. Cultivation does little, however, to conserve soil moisture, and it speeds the change of soil nitrogen into the less useful nitrate form. It can also damage the root system if done too deeply. A better alternative is mulching, and your best bet is to use an organic mulch.

Why organic? Black polyethylene mulch, while good for limiting weed growth, has several disadvantages over its more natural counterparts. Namely, the temperature beneath the plastic can reach up to 30o above the air temperature on sunny summer days. Repeated high temperatures will dry out the plant's root system unless you provide supplemental irrigation. I promise. Being one who has to "see for myself" before I believe anything, I once lost half my young plants mulched with black plastic during an extended heat wave and drought. Bushes in the same planting that were mulched with organic materials survived quite well. None of the bushes were irrigated.

I maintain at least six inches of organic mulch around and beneath my plants, adding additional organic matter each spring to make up for that rotted away the previous summer. Dried grass clippings, peat moss, buckwheat hulls, shredded leaves, straw, woodchips and sawdust are all fine to use. I don't like to spread on hay mulch, though, since it spreads weed seeds and decreases soil levels of ammonium nitrogen, upon which blueberries thrive. Never use grass clippings from lawns treated with herbicides, nor fresh clippings -- the fermentation and overheating as the grass decomposes may damage blueberry roots. Whole leaves, especially from maple and elm, tend to mat and choke off the oxygen supply to the roots. I've seen this happen in more than a few backyards. Peat moss and buckwheat hulls make an attractive mulch but are relatively expensive. Plus, peat moss crusts over, preventing moisture from reaching the plant roots, and buckwheat hulls can dry out and blow away in a strong wind. I prefer to use sawdust or woodchips. Under these two organic materials, the acidity of the soil (it should be in the pH range of 4.2 to 5.5) remains nearly constant, weeds are kept to a minimum, moisture levels and soil aeration are increased, and there's more ammonium nitrate available to plants. And because the soil temperature is moderated, the roots have more time to grow and develop. The result is a plant with greater vigor and substantially increased yields. What type (hardwood, softwood, coarse or fine) of sawdust or wood chips you use has little influence on plant growth, but it might affect the cost. Go for whatever is cheapest.

The condition of the mulch may affect the plants, however. Dry material, particularly sawdust, can absorb water from the soil when it's applied, so be sure to wet both the soil and the mulch thoroughly before use. Don't use fresh material, or mulch from the center of a pile that has sat undisturbed for more than a few months. The organic acids and other toxic compounds built up during anaerobic fermentation near the center of old piles can severely damage plants. Fresh wood chips might contain portions of undesirable plants, such as poison ivy or trailing blackberry, which could root and ruin your planting. I've seen an otherwise perfectly healthy blueberry patch overrun with blackberry vines brought in on green chips that the gardener had obtained for free from the highway department. What a deal! Also, fresh material will utilize considerable nitrogen during decomposition, robbing your plants of the nitrogen they need for proper growth.

In fact, as part of the natural process of decomposition, soil microorganisms use nitrogen to break down the mulch even if it's somewhat decomposed. This could lead to a nitrogen deficiency and stunt plant growth. To avoid this problem, apply two pounds of ammonium nitrate, six pounds of 10-10-10 or the nitrogen equivalent in fish emulsion or blood meal, for each 100 pounds of mulch, in addition to your normal fertilizer application (one ounce of a 10% nitrogen fertilizer per year of bush age up to eight years old). An even simpler method is to double the usual rate of fertilization for as long as you use the mulch.

You may spread the mulch over the entire planting, beneath each row or in a minimum two-foot radius circle beneath each bush. Just be sure to slant the mulch toward the plant to decrease wasteful water runoff. Prudent pruning

A well-managed blueberry bush should put out several new canes from its base each year, have a total of eight to 10 canes and produce new shoots at least 12 inches long on older canes. Because a blueberry plant sets flower buds only on new shoots, you must have this cumulative growth to keep the bush productive. Accordingly, in the first few years after planting I remove only damaged and diseased wood and any canes that are too low-growing to be fruitful. But by the fifth year in the field, when the plants have matured, I give the plants their first thorough pruning and continue pruning early each spring.

When pruning mature plants, I first remove all diseased, dead or injured wood, always cutting back to a bud or to a side shoot. Next, I cut old or unthrifty canes back to a low side shoot or to the ground. Any cane older than five years automatically falls into this category. They're easy to spot: the stems are about an inch in diameter near the base. To keep track of which canes are five years old, remove the oldest one-fifth of the canes each year. Absence of strong new shoots frequently means that the bush is overcrowded with old canes and/or is underfertilized.

After you've removed the unhealthy shoots and the old wood, remove all twiggy and bushy growth and any weak lateral shoots. If your bush has an open growth habit, head back canes that droop to the ground or spread far from the bush's center. If it has an upright, compact habit, be sure to thin more canes near the center.

Blueberry plants that are neglected for years will degenerate into a thick, twiggy mass of diseased and unfruitful wood. I've seen this most often in home plantings. But you can rejuvenate these old-timers and bring them back into good production. Simply cut them to the ground. You'll have no crop the first summer after pruning, but the plant will bear a substantial crop the following summer and be back in full production the second year after cutting. I've mowed my many different varieties of blueberries and never lost a single plant. In fact, I've even bulldozed a row of old blueberry plants, scraping the tops to ground level, and every one sprouted into a new bush the following spring.

But while it's difficult to kill a blueberry plant, it's all too easy to neglect one. Don't let laziness get the best of your berries. Follow the two simple practices of using an organic mulch and properly pruning the plants annually, and you'll have a bountiful crop of beautiful blues every season.

Blueberry Best Bets The following list of highbush blueberry cultivars are rated by their USDA hardiness.

Avonblue (zones 7a-9b): A southern highbush that requires heavy pruning right after flowering to prevent overbearing and to produce its medium to large, light blue fruit. The plant is small, has a spreading habit and ripens high-quality fruit about May 7 in Gainesville, Florida.

Bluecrop (4a-7a): The leading blueberry cultivar in the world. Ripens large, light blue fruit in mid-July in South Haven, Michigan. Bush is upright, moderately vigorous and consistently productive.

Blueray (4a-7a): An upright, vigorous, productive bush. Fruit is very large, light blue and of excellent quality. Ripens July 18 in Michigan and is the leading cultivar for pick-your-own operations.

Blue Ridge (7b-9a): New (1987) release especially recommended for North Carolina. Vigorous, upright bush produces large, light blue fruit that ripen about May 20 in southern Georgia. Susceptible to stem canker and mummyberry, but tolerant to stem blight.

Coville (5b-7a): Very productive with large fruits of excellent quality, ripening August 1 in Michigan. Very susceptible to stem canker in the South. Must be planted with at least one other cultivar for best production.

Earliblue (4b-7a): Early-ripening cultivar produces large, aromatic light blue fruit on upright but spreading plants. Ripens July 1 in Michigan. Fruit set may be erratic; plants very susceptible to phomopsis canker.

Herbert (4a-7a): My favorite for a home planting. It's an older cultivar with an open-spreading bush. Dark fruit ripen in mid-July in Michigan and are of very good flavor. The bush may have inconsistent yields in colder areas.

Misty (7a-9b): Southern highbush with large light blue fruit on a tall, upright bush. Good choice for low-chill areas and a good pollinator for Sharpblue. Ripens May 2 in Gainesville, Florida.

Patriot (3b-7a): Tolerates temperatures to -20oF and is resistant to Phtophthora root rot. Well adapted to the Northeast but susceptible to stem canker in North Carolina. Large, light blue fruit have very good quality and ripen in early July in Michigan.

Sharpblue (7b-10a): The #1 highbush in Florida. Dark fruit on vigorous plants; needs pollination with a variety such as Misty to ripen by April 27 in Florida.

Robert E.Gough, a former professor of horticulture at the University of Rhode Island, now lives in Oakfield, Maine, where he writes about small fruits, viticulture and tree fruits.

Provided by NGA
Reprinted with permission HouseNet, Inc.

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