Generally, plants that bloom in the winter should be trimmed only after they have blossomed, so in the early spring. The branches that grow during the next vegetation period will produce flowers in the next year. Winter jasmine should be thinned out so that the more crowded spots are removed. A light trim in the spring every two or three years supports the production of ample blossoms. Winter heather (Erica carnea) can be encouraged to produce new blooming branches with a little bit of trimming back after it blossoms. If you’d rather not get your own sheep, you can let your garden and landscaping experts tackle the task in the spring.