Growing Berries in Your Backyard
Watering. During the growing season blackberries require frequent irrigations so that they are always moist. Blackberry plants require approximately 1 to 2 inches of water per week from mid-May through October. It is best to keep the plants moist at all times without saturating the soil and rotting the roots. In general, irrigate twice a week, wetting the entire root system with each irrigation. However, during the fruiting stage or during hot and windy conditions, greater amounts and more frequent applications of water should be applied. Overhead irrigation promotes fruit rot and leaf diseases, so is not recommended for blackberries. When using drip irrigation, blackberries should be watered every day for 1 to 2 hours, longer in hot weather or when fruit is ripening.
Fertilizing. Blackberries require at least yearly applications of a nitrogen-containing fertilizer for good growth and fruit production. Apply 5 to 6 pounds of 20-20-20 or ammonium sulfate (21-0-0) fertilizer per 100 feet of row. If plants lack vigor, apply an additional 1 pound of ammonium nitrate (34-0-0) per 100 feet of row or 1.5 pounds of ammonium sulfate at bloom or midsummer, just prior to an irrigation. If you use manure or compost, apply it in the late fall or early winter to allow leaching of excess salts by rain.