I live in Toronto. My rose of sharon get 3-4 hours of afternoon sun June, July, August. Many pods do not open.
1. Do I remove them now (late November)
2.Remove them next spring?
3. Just leave them?
Thanks for your question about Rose of Sharon (Hibiscus syriacus). This is a shrub native to parts of Asia. It does well even in adverse conditions and blooms in August at a time when not many other plants are in flower, making it a popular choice for some gardeners.
When you say “many pods do not open” I am not sure whether you are referring to unopened flower buds or to unopened seed pods that form after the flowers have faded.
Rose of Sharon (RoS) requires a location in full sun, i.e. 6 hours of sunlight daily, to perform well. You say your RoS receives 3-4 hours of sun. If you are referring to unopened flower buds, then lack of enough sunlight is likely the reason. There are a couple of possible solutions: 1) dig up and transplant the shrub to a sunnier location; 2) if the shrub is being shaded by taller trees/shrubs, remove some of the limbs/stems to increase available sunlight.
A third — and in my view the most preferable — option is to replace the RoS with another, less potentially invasive shrub. A native shrub that tolerates shade and produces berries would be a terrific choice as it would provide both pollen for pollinators and food for birds and other wildlife.
I say that this is a preferable option because RoS is a notorious self-seeder and not a plant that is kind to a person’s neighbours, especially if it’s an older variety. Most of the finished blooms turn into seed pods which will open over the winter. The numerous scattered seeds are mostly all viable and will produce seedlings the following summer. One cannot simply leave the seedlings as many of them will take deeper root if left and by the end of their second year they are difficult to pull up. As the below-linked fact sheet from Ohio State University points out, “older cultivars that set heavy seed crops can self-sow to form a weedy colony of young shrubs.”
RoS is considered invasive in some parts of the United States but is not yet on any invasive lists in Ontario. However, its propensity to self-seed so prolifically in my view negates many of its benefits. There are some sterile varieties which one can plant. All of them need full sun, which you do not appear to have.
If your question was about unopened flower buds, you can just leave them. If it was about unopened seed pods the answer, if you are very attached to your RoS and wish to keep it despite your lack of full sun, is to cut off the seed pods before they have a chance to open over the course of the winter.
I’ve included some links with further information below.
What to Do if a Rose of Sharon Plant Fails to Flower (thespruce.com)
15 Rose of Sharon Varieties for Your Landscape (includes sterile varieties) – thespruce.com
THE ROSY (AND NOT-SO-ROSY) ROSE OF SHARON – Toronto Gardens blog
Gardening with Native Shrubs: A Toronto Master Gardeners Guide