Rosemary Not Blooming
Answered by: Conrad Richter
Question from: Michelle
Posted on: August 15, 1999

What conditions stimulate rosemaries into bloom? Most of my rosemary plants begin to bloom this time of year, and bloom profusely all throughout the winter until spring. I bought a pink rosemary from you two years ago, and it has not bloomed yet. It’s very healthy and has grown out nicely. How can I get it to bloom?

We are not aware of any research to answer the question of what factors control flowering in rosemary. For many plants, the controlling factors include day length or temperature or some combination of both. A well known example is poinsettia which requires cool temperatures and long nights (short days) for the colourful bracts to develop. It seems likely that temperature and day length are important because of the seasonality of flowering you noted in rosemary.

Nutrition and conditions in the root zone are often important also. Plants often exhibit reduced or no flowering when nitrogen fertility is high. These plants will show lush green growth but little or no flowering. Other plants, such as scented geraniums, can sometimes be spurred into flowering by letting the plants become rootbound or dried out a few times – as if these plants are programmed to reproduce when threatened with survival.

Physiological age seems to be important too. A juvenile plant may not flower even if other conditions are right. And the precise age at which the plant reaches flowering age can differ among the different varieties.

Our own experience is that not all plants of a given variety of rosemary will bloom in the same year, even if they appear to be of similar size and health. What factor or factors are responsible is not clear.

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