Gardeners generally grow blackberries from cuttings rather than seeds because it is more difficult to grow them from a seed. The tough coating of blackberry seeds requires special care to stimulate germination. It can take as long as six months to ready a blackberry seed for planting. To simulate the conditions that the seeds would face in the wild, the seeds must be exposed to cold temperatures for a time period that will simulate winter.
Insulate the blackberry seed with soil or sand to keep it protected from cold temperatures. Place potting soil or commercial peat moss into a bag and place the seed in the middle of it. Using outdoor soil can create a dangerous bacterial environment in a closed bag. If you use sand, purchase sterile sand.
Close the bag and place it in the refrigerator to simulate winter temperatures. The temperature should be between 35 and 40 degrees Fahrenheit. The temperature should never reach freezing to avoid harming the seed.
Leave the bag undisturbed for three to six months. This is the time period that the seed would experience in the winter.
Choose a planting area that gets full or partial sunlight and that drains well. If water is left standing on the surface for an hour after a rain, the drainage is likely not good enough to grow blackberries.
Break apart the surface of the soil and add organic fertilizer. Peat moss, potting soil or compost can be added to create a less alkaline soil that will be favorable to blackberries.
Plant the seed by pressing it into the soil and sprinkling a thin layer of soil over it.
Water the newly planted blackberry seed every few days to keep it moist until it sprouts.