Seed Collection and Preparation
The part of the rose that holds seed is called the "rose hip." Rose hips develop at the threshold of fall. Only if you stop pruning your roses will you notice their development. They are small pods that are red, orange or green. You will need to collect the rose hips in order to harvest the seeds for planting. Once you've stopped removing dead flowers, you will notice the hips start to develop. Some dead flowers remain brown and will not produce viable seeds--ignore them. A rule of thumb is to wait after the first heavy frost, as your rose hips with viable seed will be mature by that time. If you are collecting hips from different rose varieties, keep them separated and labeled according to type.
Any time after harvesting you can open the hips to harvest the seeds. A butter knife will work fine. Cut the hip in half and drop seeds into a glass of water that has a teaspoon of bleach added. Seeds that drop to the bottom are viable for planting. Floaters are not, so discard them.
Seed Planting and Germination
Cold stratification is the process of exposing seeds to a temperature of approximately 35 degrees Fahrenheit. You can do this by placing them in your refrigerator. Store them by placing them inside of a folded paper towel that has been moistened with half-part purified (bottled) water and half-part bleach, then placing them in a zip-lock bag. Don't forget to mark the varieties if you are using more than one kind of rose. Keep them in the cold for 45 to 60 days.
You can plant seeds immediately after stratification if there is no danger of a heavy frost. Use a mixture of 50 percent planting soil and 50 percent vermiculite, and place seeds a half-inch apart from each other. Use small, shallow trays as long as there is good drainage. Place them in direct sunlight, or use grow lights for 16 hours a day. Keep moist with regular watering.
The third leaf that appears from the soil is the true rose leaf. After two or more leaves are visible, plant the seedling in its own pot. A 3-inch plastic pot will do. Make sure you have it in direct sun or are using grow lights. Help it along with half a teaspoon to 1 quart solution of Miracle Grow and water.