How to Grow Blackberries From Rootstock

Select the site for your blackberry plants. Choose a sunny location that provides protection from wind. Slopes provide cold air drainage, but avoid southern slopes, which may cause buds to open too early.

Remove all weeds from the planting site. Test the soil in your selected site. Blackberry plants require soils with pH levels between 5.5 and 6.5. Follow the instructions on your soil test results to adjust the pH level of your soil. Amend your existing soil to create a rich, loamy medium by tilling in organic matter, such as dried leaves or sterile compost. Create rows for planting your new rootstock. Make the rows at least 8 feet apart. Dig trenches about 9 inches deep.

Plant the dormant blackberry rootstock in early spring. Soak the root segments in a bucket for several hours before planting them in the prepared soil. Place the root cuttings at least 2 feet apart in the rows, laying them horizontally at the bottom of the trenches. Fill in the trenches with backfill. Do not allow any part of the root cuttings to extend above the surface of the soil. Gently tamp down the soil over the roots.

Water the blackberry plants to the level of the roots. Keep the soil slightly moist, not soggy, during the first year of growth. Established, mature plants can tolerate dryer soil conditions, but may require supplemental water during extended droughts. Water deeply whenever the soil becomes slightly dry near the roots.

Fertilize your blackberry plants between four and eight weeks after you plant them. Use a fertilizer that contains ammonium nitrate, following the instructions on the fertilizer label. During subsequent years, fertilize them just before new growth begins in the early springtime and again in May.

Prune the lateral branches of your blackberry plants in the winter, after the plants enter their dormant stage. Cut the tallest lateral branches back to about 12 or 14 inches long. Remove the canes that produced the fruit even with the surface of the soil.