Rose of Sharon, also known as "shrub althea" or Hibiscus syriacus, is notorious for sending seedlings sprouting up everywhere. Not surprisingly, this deciduous flowering shrub with late-summer blooms is also easy to start from seed. Is this ability to spread a nuisance or a gift? It depends on your perspective. If you don't want the plant to spread, you have to get rid of the seedlings as soon as they come up. On the other hand, if you like your rose of Sharon enough to plant it elsewhere, you can let Mother Nature help you spread the wealth.
How to Get Rid of Rose of Sharon Seedlings
Rose of Sharon spreads by putting out lots of seeds in fall, and the seeds sprout readily the following spring. The result is rose of Sharon seedlings growing all over your lawn or planting bed, whether you want them or not. If this natural spread is undesirable, how do you get rid of these "volunteer" rose of Sharon seedlings?
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It is much easier to solve this problem through preventive measures rather than tackling the problem after the fact; that is, before the seedlings do much growing. When the flowers of your shrub are done blooming, simply deadhead them. This will nip seed production in the bud and eliminate all those annoying seedlings. Make sure you remove not just the flower, but also the developing seed pod at its base. The seed pods develop in October and take 6 to 14 weeks to mature, so you have a little time once the blooms have withered.
If you fail to implement this preventive control measure, you will have a tougher row to hoe. The fully developed seed pods eventually dry out and split open, dropping the seeds near the parent plant. In this way, rose of Sharon readily forms clumps or colonies, which is why it can be useful as a hedge but also why it's considered invasive in some climates. If spring arrives and your rose of Sharon shrub has lots of little seedlings sprouting all around it, simply pull out the seedlings as soon as possible.
Will Herbicide Work?
Some gardeners wonder about spraying the young rose of Sharon volunteers with an herbicide. One method is to “paint” an application of something like Ortho’s woody plant herbicide onto the little rose of Sharon plants. In this case, “paint” means applying herbicide directly to individual plants instead of spraying the general area of the new plants; if any errant spray lands on the parent rose of Sharon shrub (or any other desired plants), the herbicide will harm them. However, this method is not much easier than hand-pulling, which is both effective and non-toxic.
Alternatively, you can try smothering the new rose of Sharon plants with a tarp or prevent them from germinating by using a pre-emergent herbicide, as you would for crabgrass, in the spring. The smothering method might be viable in a sparsely planted bed. It is not an option if the germinating activity is happening on a lawn because the tarp would also smother the lawn. Pre-emergent herbicide makes sense only if you failed to deadhead in the fall to prevent seed spread. Keep in mind that a pre-emergent herbicide will prevent all seeds from germinating, not just those causing a problem.
How to Start Rose of Sharon From Seed
If you're interested in propagating rose of Sharon by seed, you can simply let nature do the work for you! This bush is easy to grow from seed, so let this fact work to your advantage. Just allow the seeds to drop on the ground in fall and winter, of their own accord, and wait for them to germinate in spring. Then, dig up your new rose of Sharon plants and transplant them to your desired location.
Alternatively, you can collect the seeds as they drop from the shrub's seed pods. Seeds must be fully mature to grow into new plants, so wait until they naturally drop from the seed pods. You can cover the pods with nylon bags to catch the seeds as they fall. In spring, plant the seeds 1/4 to 1/2 inch deep in humus-rich soil. Give them full sun and water them deeply. Watch out for birds eating exposed seeds.