Emerald Cedars Dying



We have been experiencing Emerald cedar die off for two seasons now and it’s progressing from one tree to the next. As far as we can tell, it’s not an issue of over or underwatering. I’m trying ti save the trees that are turning yellow now but unsure if a fungicide is the best approach. Am at a complete loss as to what to do. The trees are roughly 10 years old and get lots of sun. I was thinking hydrogen peroxide to see if that helps..


Hello, thanks for your question.

Toronto Master Gardeners get a lot of questions about dying Emerald Cedars. Most of the time the issue is insufficient and/or inconsistent amounts of water. Most of the Emerald Cedars sold in Ontario are grown in BC, where it is both milder in winter and cooler in summer and wetter than here. They also can suffer transplant shock and there is the trauma of traveling here from BC.  The fact that your cedars are 10 years old and these issues you describe have been occurring for only the last 2 years, makes me think you are probably right, it’s not underwatering. But, we are having very hot dry summers now and cedars are quite shallow rooted. If your soil is a bit sandy the trees would also dry out more quickly.

I guess you are thinking of hydrogen peroxide because you think the trees might have a fungus. You didn’t give any evidence of having seen fungal diseases or insect pests. The following statement was taken from a Fact Sheet published by the US Environmental Protection Agency: “Hydrogen peroxide, well known as an ingredient in disinfectant products, is now also approved for controlling microbial pests on crops growing indoors and outdoors, and on certain crops after harvest. This active ingredient prevents and controls bacteria and fungi that cause serious plant diseases. Hydrogen peroxide breaks down rapidly in the environment to oxygen and water, and is not expected to cause adverse effects to humans or the environment when users follow label directions.” However, I would not use this product on my plants unless there was definite evidence of fungal infection and you know what the fungus is. Not even specialized fungicides kill every fungus. You need to be very careful to mix up the right concentration of hydrogen peroxide because too strong a concentration will kill the plant. I would use the most commonly available concentration of hydrogen peroxide, which is 3% and dilute it as described here. Take a small part of one tree and test it out, before you spray all of them.

1 cup 1 and 1/2 teaspoons 7 to 10 drops
1 quart 2 tablespoons 1/2 teaspoon
1 gallon 1/2 cup 2 teaspoons
5 gallons 2 and 1/2 cups 3 tablespoons plus 1 teaspoon
10 gallons 5 cups 6 tablespoons plus 2 teaspoons
20 gallons 10 cups 3/4 cup plus 1 tablespoon plus 1 teaspoon
bathtub (approx 25 to 35 gallons) * 12 to 17 cups 1 to 1.5 cups

* bathtub sizes vary. It is okay to use more water and/or less peroxide.

Here is a link to a similar question answered previously by Toronto Master Gardeners:


This is a brief overview of some of the issues that may be causing your cedars to turn brown; if you search on our “Ask a Master Gardener” website using the word “dying emerald cedars”, you will find several other posts attempting to answer this question.

The following fact sheet from the British Columbia Department of Agriculture is really excellent. The pattern of symptom development/distribution can help you decide whether the problem is infectious or non-infectious. It has pictures of common insect pests, diseases and foliar blights. It also talks about environmental, soil and chemical factors.

Dying cedar hedges – what is the cause?

I’m sorry I couldn’t be more specific and tell you this is the problem and this is what you should do. Cedar hedging can be challenging to grow.