How to Grow Rosemary: A Toronto Master Gardeners Guide

Rosemary (Salvia rosmarinus, formerly Rosmarinus officinalis). Rosemary is a perennial herb, which pairs particularly well with lamb dishes and can be used for making flavoured oils or vinegars. Rosemary is native to the Mediterranean and only hardy to Zone 8. In Ontario, it is best grown as an annual or in a container that can be moved indoors before the first frost.

Rosemary is most easily propagated from cuttings, which will root quickly if taken in the spring when growth is vigorous. To grow rosemary outdoors, plant it in light, slightly acidic, dry-to-medium, well-draining soil. Rosemary prefers full sun and has moderate drought tolerance, but should not be allowed to dry out completely.

Moving rosemary plants into pots from a garden bed is rarely successful so plants intended for overwintering indoors should be container-grown. Containers must have good drainage since the plant should never be waterlogged. Feed plants in containers with a balanced fertilizer after they have finished flowering and, at the same time cut them back to ensure a bushy plant.

To overwinter indoors, rosemary does best in a sunny but cool position with good air circulation. Allow the plant to become nearly dry between waterings. Once danger of frost has passed in the spring, replace the soil in the pot then gradually acclimatise it to full sun outside.

Rosemary being overwintered indoors frequently becomes infected with mildew. To help prevent this, ensure good air circulation and humidity and water the soil not the leaves. Remove any mildew-Infected leaves or shoots to slow its spread. An approved fungicide may be used if necessary. (Richters herbs Q and A; U of Illinois extension blog)

Leaves or shoots can be harvested at any time during the growing season and are used fresh or dried.

Disclaimer: Toronto Master Gardeners does not advise or recommend herbs for medicinal or health use. Any information in the recommended resources should be regarded as being for educational purposes only and should not be considered as a recommendation or an endorsement of any medical or health treatment.

For more information:

Cornell Cooperative Extension of Suffolk County: https://blogs.cornell.edu/ccesuffolkligardening/tag/rosemary/

 

Richters Herbs Q and A  https://www.richters.com/show.cgi?page=QandA/Growing/19980331-70.html

RHS Grow your own Herbs https://www.rhs.org.uk/advice/grow-your-own/herbs/rosemary#nav-get-involved

University of Illinois Extension https://web.extension.illinois.edu/herbs/rosemary.cfm

University of Massachusetts-Amherst Extension Greenhouse Crop and Floriculture program

https://ag.umass.edu/fact-sheets/rosemary-container-production-for-december-market

Date revised: December 2021

Prepared by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics.  Toronto Master Gardeners are part of a large, international volunteer community committed to providing the public with horticultural information, education and inspiration.  Our goal is to help Toronto residents use safe, effective, proven and sustainable horticultural practices to create gardens, landscapes and communities that are both vibrant and healthy.

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