If you want to add more thornless blackberries plants, but you don't want to spend the money, you can propagate them. Apache and Navajo are two thornless varieties that will remain thornless when propagated. Propagating your own blackberry plants will give you healthier plants and more berries. Although the blackberry plants are perennials, they have a lifespan of around 15 years. Learning to propagate your own is a wonderful way to keep that supply increasing throughout the years.
Find a long length of stem from your blackberry plant in mid-September. The perfect branch to begin a root cutting is about a year old and has the diameter of a pencil. It should have no damaged areas.
Take the stem and bend it toward the ground. Where the tip meets the ground, mark that spot with a stick or rock. Tie a piece of twine or string around the shoot so you can easily locate it again.
Dig a hole with your spade in the place that you marked. Make the hole about 4 to 5 inches deep.
Grab the stem that you chose and measured to mark the hole. Gently bend it toward the hole you just dug.
Place the tip into the hole. Fill the hole in with the soil and press it down firmly.
Set some rocks or bricks on the soil next to the branch. This will help hold the branch in place. You may remove them in three to four weeks; by then, your thornless blackberry should grow roots.
Water the site well. Keep the soil moist, but not soggy wet.
Watch and water the tip for several months. When a shoot grows, you will know roots are developing. Care for the tip in the same fashion as you do for the parent plant.
Take a pair of pruning sheers and cut the stem from the parent plant about 10 to 12 inches from the blackberry plant. Do this when the spring comes.
If you are planning to replant your new blackberry plant, do so with care. The roots do not like to be disturbed. With a spade, try to dig the entire root ball keeping the soil intact. They like to grow in soil that has a pH level of 5.5 to 6.5. They need good drainage to grow.
If you want a true thornless blackberry that will stay thornless when propagated, check the variety you have. Some thornless blackberries are chimeras. When propagated, they will revert to a type that has thorns. The parent plants are only thornless on the outer layer of cells. Any root cuttings taken from them will be thorny. Blackberries are susceptible to redberry mite infestations. These mites cause the fruit not to ripen uniformly. When the fruit is infected, you will see bright red or hard green druplets. During the winter, the red mites live in the cane bud scales. To control red mites, apply miticides in the fall and just before the buds form in the spring.