My Rose of Sharon only bloomed on one side last year and right now, there is no sign that it will bloom this year. What can I do to keep my tree alive.
Thank you for contacting the Toronto Master Gardeners.
First of all, it is not unusual for a Hibiscus syriacus or Rose of Sharon tree to look bare right now. These trees leaf out late in Spring and, given the cool temperatures we have had this year, are probably going to take their time to wake up. If you want to double-check, use your thumbnail to gently scratch the outer brown bark on a few branches to see if there is green plant tissue underneath.
Rose of Sharon prefers full sun, soil that is rich and moist, and is hardy to USDA zone 5 (i.e. Canadian zone 6). Since it is borderline hardy in Toronto, it is best to give it a sheltered location to protect from winter kill. Giving it a good 2-3 inch layer of organic mulch around the root zone in the Fall will also help. In late Spring, after it has leafed out, prune out the winter damaged branches and apply a balanced 10-10-10 fertilizer to give it a head start. A mid-summer application of a low nitrogen 0-10-10 fertilizer will promote root health and flower production. Do not apply fertilizer after August as this will encourage tender new growth that will not overwinter. Water deeply but not too frequently, and take care not to let in sit in wet soil or the roots will drown. Amend the soil regularly to keep it humus rich and healthy.
You noted that your Rose of Sharon tree flowered only on one side last year. From your photograph, the tree looks fine. Is it possible that only one side of your tree is getting enough sun? Were there buds on the side that did not flower? Did you observe any signs of pest or disease? If it happens again, write us back with your observations, and we will be happy to help.