Emerald cedars and black walnut tree


Cedar hedge has grown thin and is brown in one spot that is located close to a black walnut tree. Is this type of cedar at risk from the toxicity of the tree?


Thank you for contacting the Toronto Master Gardeners with your question about your ailing cedar hedge and possible black walnut toxicity.  As you allude to, black walnut trees and other members of the same plant family (Juglandaceae) have a chemical in all of their plant parts that can affect the growth of some other plants.  However, Emerald cedars (Thuja occidentalis ‘Smaragd’) and cedars in general (Thuja spp.), are not typically affected by juglone.  More information about plants that are tolerant of juglone is available through the Morton Arboretum here and one of our Gardening Guides Toronto Master Gardeners, Juglone.

There may be other reasons to consider regarding the browning of your Emerald cedar.  Many gardeners have similar questions about their cedars. Problems can be related to moisture, light, soil nutrients, factors like road salt and wind as well as insect pests.  This answer to a previous question on our website should provide you with information about optimal care requirements and insects / pests that may be a problem Care of cedars.  Please don’t hesitate to contact us again if you have further questions.

May 6, 2021