Is it okay to fertilize my rhodies, azaleas, and roses in September? I missed
doing it in August.
Generally speaking, it is best not to fertilize your shrubs after mid-summer. The tender new growth that results is susceptible to frost, disease, and insects just at the time of year when the plant is beginning to shut
down. This is also true of roses, which are even more tender and susceptible than rhododendrons and azaleas.
An article by Terri Richmond (British Columbia) on the American Rhododendron Society website, entitled Fertilizing Rhododendrons the Organic Way supports the practice of fertilizing in spring. (Keep in mind that azaleas are in the same genus as rhododendrons.)
Oregon State University Extension suggests that budbreak in spring is a good time to fertilize roses, just as new growth is beginning. Stop fertilizing in late summer. Oregon State University also weighs in on fertilizing rhododendrons (if needed, in spring shortly after flowering, and preferably with organic fertilizer).