How to Grow Basil: A Toronto Master Gardeners Guide

Basil (Ocimum basilicum). Basil is a tender annual herb valued in many cuisines. There are several different cultivars of basil, the ones with purple leaves being especially ornamental.

Cultivation:  Classic Genovese basil may grow 60 centimetres tall or more, while other cultivars are shorter. Sow seeds in pots with a moisture retentive compost or in the ground as soon as the soil warms up. Basil prefers full sun. Keep the soil evenly moist but not wet. Fertilize in-ground plantings a couple of times in the season with a 5-10-5 (N-P-K) product. Fertilize container-grown basil every three to four weeks if outdoors, or every four to six weeks if indoors. Pinch out the growing tips to encourage a bushy plant and remove flower buds to inhibit flowering. Basil is quick to bolt (flower prematurely) so make repeat sowings for a season-long supply. Harvest fresh leaves at any time but ensure enough leaves remain on the plant for it to continue growing. Basil is not frost hardy but can be sustained into the cooler months on a sunny windowsill. Basil can also be grown from cuttings.

Classic Genovese basil is highly susceptible to a downy mildew that will kill the plant. Water from below to avoid wetting the leaves. If you detect downy mildew, remove any uninfected leaves for use, then dispose of the affected plant in the household garbage. Some cultivars are more resistant and this characteristic may be noted in seed catalogues.

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:

RHS ‘Herbs-Growing’  https://www.rhs.org.uk/advice/profile?PID=679

RHS ‘Grow your own Herbs’ https://www.rhs.org.uk/advice/grow-your-own/herbs/basil

University of Minnesota Extension https://extension.umn.edu/vegetables/growing-basil

Herb Society of America (HSA) https://www.herbsociety.org/hsa-learn/hsa-publications/hsa-quick-fact-sheets.html

Richters https://www.richters.com/Documents/d0005_Richters_2021CAD.pdf

Wisconsin Horticulture, Division of Extension https://hort.extension.wisc.edu/articles/basil-downy-mildew-2/

U of Massachusetts Center for Agriculture, Food and the Environment  https://ag.umass.edu/vegetable/fact-sheets/basil-downy-mildew

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.

Statement on Invasive Plants: When choosing plants, avoid invasive plants, which can spread quickly and dominate gardens.  Invasive plants are sold by nurseries, big box stores or even at community plant sales.  Invasives may already be present in your garden.  They can invade gardens by spreading from under a neighbour’s fence or may be transported by wildlife.  For beautiful, sustainable options to invasive plants, see the Ontario Invasive Plant Council’s “Grow Me Instead – Beautiful Non-Invasive Plants for your Garden” at https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/ before purchasing or accepting “gifts” of plants.

Statement on Home Remedies: The Toronto Master Gardeners do not recommend home remedies, as these have not been proven effective through scientific investigation, and may even damage other living organisms in the soil or plants in your garden.  There are other garden friendly options you can use.

If you have further gardening questions, reach us at our gardening advice line 416 397 1345 or by posting your question here in the Ask a Master Gardener section.  To book Toronto Master Gardener volunteers for talks, demonstrations, advice clinics, or other services, please contact us at 416 397 1345  or bookamg@torontomastergardeners.ca