The age of a plant, the soil type, and the time of year will dictate watering needs of a blackberry plant.
Methods of Irrigation
If you have just a few or several blackberry plants, hand watering is probably best. Just make sure to avoid splashing the foliage or berries of plants with water, which can cause berries to rot. Instead, provide water around the base of the plant out beyond the perimeter of the plant. When growing blackberries in long rows, it's more convenient to irrigate with a soaker hose or drip irrigation system.
Watering Newly Planted Blackberry Plants
Watering is critical for first-year blackberry bushes. Of course, you need to water them well after you plant them, but their water requirements after that are pretty straightforward. Your young blackberry bush will like the soil moist, but not constantly soggy or wet soil, which can lead to root rot and death of the plants. The type of soil your blackberry plants are growing in will pretty much dictate water use. When growing in clay-based soils there won't be as much a need for supplemental irrigation. When growing in quick-draining sandy soils, more frequent watering may be required to keep soil moist during the first growing season.
In the absence of rainfall during the hottest time of the year, smaller plants should receive two 6-hour drip irrigation sessions per week or at least one good deep soaking per week when watered by hand.
Watering Established Blackberry Plants
When established, blackberry plants are fairly drought tolerant. That being said, lack of sufficient water just prior to and during the harvest season will seriously reduce the crop and quality of fruit your blackberry bushes produce. This will not only affect the current year’s harvest but also the following year’s crop as the water shortage will limit the production of desirable fruiting canes called "primocanes."
Because they are larger and expending more energy to produce more fruit, mature plants require more water and more frequent watering than young plants. Mature plants should receive about 1 inch of water per week from rainfall or irrigation, and twice that amount during the fruiting period. Just keep in mind that soil should be moist but not soggy wet, which can lead to root rot causing death of plants.
If using drip irrigation, water mature blackberry bushes 1 to 2 hours every day, and longer when the weather is hotter and drier, or when the blackberry fruit is beginning to ripen.
Benefits of Mulch...
Mulching around plants with a 1- to 2-inch layer of shredded wood mulch, pine bark mulch, or pine straw, aids in water retention and weed control.
