Cotoneasters (Cotoneaster spp.) can be either evergreen or deciduous and range from low-growing varieties for use as ground covers to tall shrubs that reach heights of 25 feet. Cotoneasters produce pink or white flowers in spring, followed by showy red or black berries. Extract the seeds from ripe berries in fall and plant the seeds the following spring. Cotoneaster grows in U.S. Department of Agriculture plant hardiness zones 5 through 7.
Place a handful of ripe, plump berries in a piece of cheesecloth or muslin. Gather the cloth around the berries, then twist the cloth to hold the berries securely. Rinse the berries under cool, running water, gently squeezing the cloth until the water runs clear. The berries are ripe in fall.
Place the seeds in a plastic bag along with a large handful of moist peat moss or vermiculite. Place the bag in a warm room where the temperature is between 68 and 77 degrees Fahrenheit. Leave the seeds for four to eight weeks, which provides time for the hard outer coating to break down.
Transfer the bag of seeds to the refrigerator and allow the seeds to chill for one to three months. Plant the seeds in spring when all threat of frost has passed and outdoor temperatures are between 59 and 68 F.
Fill a celled seed tray with a gritty potting mixture, such as a mix of 3 parts peat moss, 1 part fine bark and 1 part perlite. Water the potting mixture until the medium is evenly moist but not saturated.
Plant one cotoneaster seed in each cell, planting it at a depth of approximately twice the diameter of the seeds. Cover the seeds with 1/4 inch of vermiculite.
Cover the tray with clear plastic or slide the tray into a plastic bag to keep the potting mixture moist and warm. Place the tray in a shady, protected area. Check the tray often often and water lightly if the potting mix feels dry.
Transfer each seedling into a 3- to 4-inch pot filled with commercial potting soil when the seedlings have a healthy root system and the plants are large enough to handle -- usually the spring after planting the seeds.
Place the cotoneaster in a sunny spot for at least another year before planting it in the garden. Continue to water as needed to keep the potting soil slightly moist.