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If you grow Rose of Sharon from seeds you harvest yourself, you may find that the newly grown plant doesn't look exactly like its parent plant. Gardeners say the plants ‘don’t come true’ when this occurs. If you want to try growing from seed (regardless of what the new plant will look like), you should try looking underneath the existing plant first, as your Rose of Sharon may have self-seeded.  See if there are any seedlings waiting for you that you can dig up and replant elsewhere. This will save you the effort of growing the plant from scratch. When you do this, you might like to hoe or pull out the other seedlings so that your garden isn’t overrun with Rose of Sharon! If you prefer to plant your own Rose of Sharon seeds, wait until the pods are brown and mature before harvesting them.  Some gardeners plant the seeds outdoors in the fall and let them get going over the winter. Other gardeners will start the seeds off indoors about a month before they expect the last frost. Regardless of whether you are planting the seeds indoors or outdoors, you should sow your seeds in a seeds compost. Moisten the compost, lay the seeds on top and cover with about a quarter inch of dry compost. Spray with water. If you start the seeds indoors, make sure to place them somewhere light but out of direct sunlight, such as an indoor window ledge that doesn't get direct sun. For both indoor and outdoor seeds, keep the compost moist until the seeds germinate in about 2 to 3 weeks.
Be aware that plants grown from seed may not look like the parent plant. Look underneath your existing plant for any seedlings. Wait until the pods turn brown before harvesting them for seeds. Sow your seeds in a seed compost. Keep the planted seeds moist and in a bright location.