Also known as saltspray rose or beach tornado, Rosa rugosa is a woody shrub with a growth potential of 2.4 metres (8 feet). This hardy rose plant is a native of China that produces white or pink blossoms, depending on variety. The Rosa rugosa also produces 25-mm (1-inch) hip fruits, which ripen to bright red in the late summer. The tiny, ripe hip fruits are bursting with seeds that can be harvested to produce young Rosa rugosa seedlings.
Collect the hip fruits at the end of the summer. Peel open the fruits to reveal the inner seeds. Place the hip fruits in a fine-meshed strainer and separate the pulp from the seeds under a lukewarm stream of water.
Set the Rosa rugosa seeds on a paper plate to dry for approximately two to three days. Fill a plastic baggie with damp peat moss, and drop the Rosa rugosa seeds into the baggie after the drying period. Seal the baggie and place it in your refrigerator for 120 days. This chilling period improves germination.
Fill seed starter trays with damp potting soil and remove the baggie from the refrigerator. Push one Rosa rugosa seed 6 mm (1/4 inch) down into the soil in each cell. Cover the tray with its lid, set it in an area that receives bright, indirect sunlight, and maintain a temperature of at least 24 degrees. Lift the lid periodically to moisten the soil with a spritz of water from a spray bottle.
Remove the lid when the Rosa rugosa seeds sprout. Chilled seeds usually begin to germinate within four months. Continue to supply the seedlings with plenty of bright, indirect sunlight, warmth and water.
Transplant the Rosa rugosa seedlings into 15-cm (6-inch) pots when they develop their second set of leaves. Plant the Rosa rugosa plants outdoors in the spring, after their first indoor growing season.
If you do not have access to bright, indirect light, set the pots under a grow light. A plant heating pad set to 24degrees Celsius keeps the seeds warm if indoor temperatures fluctuate. Keep in mind that the 120-day stratification or chilling period is essential to the germination of Rosa rugosa seeds. Without stratification, the seeds can take up to two years to germinate.
Do not overwater the Rosa rugosa seeds. Light spritz during germination is all they need. Standing water causes the seeds to rot, spoiling any chance of germination.