Blueberry Prescription (cont)
By: Lee Reich
Maintaining the Plants
Prune in winter. A highbush blueberry stem remains most productive for four to six years, depending on climate. When stems reach 1 to 1-1/4 inch in diameter, they become less productive. So first, cut away, near ground level, the oldest stems. Also shorten young, weak stems, and remove older twiggy growth. Remove some stems in the center of the bush if they crowd, and shorten or remove stems that droop to the ground. Some highbush varieties, such as 'Cabot' and 'Pioneer', produce excessive fruit buds on each shoot, so shorten the fruiting stems until only three to five of the fruit buds remain.
Prune rabbiteye blueberries slightly less than you would highbush blueberries. Cut away just enough to keep the bush from growing too tall and its center from becoming too shaded, by lopping old, large stems to the ground.
The best fruits of lowbush blueberries are borne on the youngest stems, especially those growing directly from the ground. Stimulate new stem growth with severe pruning by cutting the plants to the ground every second or third winter. Plants won't bear the season following pruning, so if you want fruit every year, divide the planting into halves, or thirds, and prune alternating sections each year.
Yearly Soil Upkeep
Annual attention to the soil keeps blueberries healthy and productive. Monitor soil acidity, and if it rises too much--or if you notice young leaves yellowing between their veins--sprinkle sulfur on the ground out to the drip line. Also, replenish mulch, and remove weeds that compete for nutrients.
Fertilize in late winter if growth was poor the previous season. Avoid fertilizers like sodium nitrate (a component of many organic fertilizer products) that make the soil more alkaline. Soybean meal or cottonseed meal, at 2 pounds per 100 square feet, is ideal. If you use concentrated fertilizer, apply the equivalent nutrient content in two applications--one application in early spring and one in late spring. In general, I recommend you avoid concentrated fertilizers, because blueberry roots burn easily.
The way to tell berries that have just turned blue from those that have been on the bush for a few days is to tickle the clusters: Only fully ripe berries will drop into your hands.
Making Soil for Blueberries
If your soil is alkaline, as in many areas of the West, it isn't feasible to acidify it sufficiently for blueberries but you can still grow them by making soil. Excavate a hole 2 to 3 feet deep and 6 feet wide. Fill it with a mix of equal parts of peat moss and sand. Because both peat moss and sand are nutrient-poor, fertilize annually with fertilizer and soybean or cottonseed meal to supply mostly nitrogen, and maintain a mulch of any organic material over the surface. If you irrigate, and your water is also alkaline, acidify it with 2 teaspoons of vinegar per gallon of water.
Photography by National Gardening Association