There are many reasons to prune a blueberry bush, but let’s begin with
the two most important. As with nearly all fruits, as time goes on these perennials will begin to produce an overabundance of small sized fruits, called runts. Allowed to its own devices, the plant will become clustered with smaller and smaller twigs which will yield smaller and smaller berries. By periodically removing these older systems, we allow for the production of new branches which will set better and larger fruits. The result will be less berries in number, but larger ones, often with higher overall yields.
Secondly, a fruiting bush will become overcrowded with new growth to the detriment of the plant’s overall health. Crowding, for instance reduces airflow, and airflow thwarts disease and insect pressure. Mildews and cankers are often less an issue with a more open structure, which this thinning produces. It also makes harvest, or need be spraying, easier to accomplish. Access to sunlight transmitted will also allow for quicker drying of surfaces, and additionally aid in fruit ripening. Fruit buds often develop only when a certain amount of light reaches developing buds; this phenomenon occurs within a self- shading plant as well as a plant shaded from another object.
There is also evidence that by reducing the number of fruit, and therefore seed production, there is less of a tax on the plant. This results in more nutrients going to the remaining fruit, and to the plant’s reserves. Thinning can also accomplish this task, but will not allow for the additional benefits of wood removal for circulation and would prove prohibitively laborious.
Pruning Specifics :
- We suggest all pruning be done in the late winter/early spring. This is particularly important in area in US zone 4 or colder. It should absolutely be done only during the dormant season, which significantly reduces the incidence of pathogen spread. Pruning when the plant is in growth removes far more of the reserves (held in some proportion in the root system) since these factors are now active in the portions being removed. The only exception is when damage has occurred during the growing season. When fall pruning is done, even if dormancy (ie- leaf drop) appears to have set it, winter damage is likely to occur. Since pruning stimulates cell activity, a delay in true dormancy (hardening off) tends to be the case. Studies have shown a higher incidence of winter damage in many so called hardy species following fall pruning in cold climates. Incidence is even more prevalent in blocks of higher fertilizing rates.
- No pruning is necessary until several years after planting. This is dependent upon the vigor and growing conditions of the bush. In our climate of zone 3 and using half-high cultivars (high-lowbush crosses), we began pruning only after year 4 or 5.
- Begin the operation by removing the damaged or obviously diseased branches. Although some growers use the technique of removing dead twigs by crumpling them with gloved hands, we do not recommend this due to the wounds that occur with this practice. Always use well sharpened and clean pruning shears (secateurs).
- Monitoring the fruit crop for proper size, and observation of seasonal disease issues should be part of the decision making process of what and how much to cut. In general, cuts for bush fruits should be made at soil level, not in the canopy. This means removing the entire system, trunk to tip, and leaving no stump. The desire here is to keep an average of 4-6 vigorous canes in place, though the total of canes in a mature bush may reach upward of a dozen and still be fine, provided the bush isn’t overly crowded. It may seem radical to remove such a large piece of your bush, but the plant will respond with at least 1 and often more powerfully vigorous replacement shoots sometimes growing many feet in a season. Generally these canes which are removed measure an inch or greater in diameter at soil level. Remove also any obviously weak shoots or canes, preferably at ground level. Some twig removal on remaining branches should also be done if they rub against their neighbors, which will lead to injury and disease.
- Whenever diseases is suspected, be sure to disinfect shears, between cuts ideally and between plants absolutely. Although there is much less chance of disease transmission in the cold dry conditions of winter, it is still possible.
- Dispose of all cuttings. Diseased prunings should be burned or buried. Other prunings should be composted, or cut into small enough pieces as part of the mulches surround the plants.
- If a purpose of the bush is in producing a hedge, the technique is a bit different. As all heading cuts (ie- giving the bush a haircut instead of removing large branches) produce more branching, they will give a fuller character indicative of the landscape hedge or bush. Keep in mind this will drastically reduce your crop since fruiting occurs on newer (end) growth. However the beauty of a hedge like blueberry may make pale in comparison the crop per se.
By pruning yearly (after establishment period) in addition to proper growing maintenance and nutrition, bush fruits can last for decades. Visit them regularly and observe them, not only when it is harvest time. You will be rewarded.