Dying and Browning Emerald Cedars

(Question)

Hi,

I planted 26 emerald cedars at the end of May and while a couple had some browning most looked lush and healthy in all spots. Now, 3 or 4 appear to be dead and others seem to be following suit.

They are in a trench 2.5 ft wide and 2 ft deep that is almost entirely triple mix (top 18 inches) and they received bone and blood meal in the trench before planting. They have 2-3 inches of mulch but always 3-4 inches away from the trunks.

I have tried different watering forms (soaker hose, spray nozzle) and can’t seem to get them to bounce back. They received the soaker hose for about an hour at a time when I was using it but they got worse so I went back to 3 minutes of spray with a garden hose per tree twice a week. I have also applied miracle grow for acidic loving plants and sprayed with insecticide.

This week 4-5 more have started turning brown and I’m scared they won’t bounce back and I’m going to lose them all, almost like a bug or disease is spreading through them.

Even the brownest of them have pale green foliage on the inside so I’m hoping I can save them. Am I overwatering? Under watering because of the heat? Was it the wrong fertilizer? Any help you could provide would be fantastic!

Also, they get full sun and are used as a hedge and were planted 2 ft off the fence line.

The ones in the left of the photo were the first to go, the ones in the right are starting. Help please!!

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(Answer)

You are not alone in your questions about your Emerald Cedar hedge – the Toronto Master Gardeners receive many questions on the care and feeding of these popular hedging plants.

Soil quality is important, of course, and adding organic material really helps to give your new plantings a good start.  However, it is generally recommended that you use the soil that was removed from the planting hole to backfill, adding triple mix or other organic material as top dressing.  The reason for this practice is that when the roots encounter the high nutrient soil around the root ball, the tree is less likely to send out its roots looking for nutrients and water, leading to a smaller, less stable root structure.  When the roots reach the garden soil itself, their growth may be slowed and their nutrient intake reduced, resulting in stress to the plant, which in turn can result in browning.  If your soil is clay, this stress to the roots, and to the plant itself, may be more pronounced.  This may be what your hedge is experiencing.

It is great that you are mulching under your hedge: a layer of mulch will hold moisture in the root zone, deter weeds and shade your cedars’ roots, and as you have done, should be kept away from the trunk of the tree.  Top dressing with organic material every year is also a good practice to maintain the nutrient level of your soil.

Watering deeply and thoroughly (at least once or twice a week after planting, especially in these hot summer conditions) is key so that your cedars’ roots can take hold and spread.  This is much more effective than frequent spraying or light watering, and can be done easily by using a soaker hose along the base of the cedars for several hours to ensure that the moisture reaches into the roots of the plant.  Watering should continue well into the autumn until the ground is frozen to maintain adequate moisture through the winter.  Cold winter winds can desiccate the foliage – once the ground is frozen, your cedars cannot take up moisture to replace what is lost from their foliage.

Deep, thorough watering can also help the roots in the root ball to separate and penetrate into the soil after planting:  plants that have been in their containers for some time can often be root bound – that is, their roots circle around the pot and are quite tightly packed.  If you did not loosen, tease out, or separate the roots somewhat before planting, your cedars may be experiencing some stress as the roots move into the garden soil.

Fertilizing the hedge with a 30-10-10 formulation three times in the growing season (May, June and July) is appropriate. It is very important to follow exactly the directions for applying fertilizers so that they are absorbed into the soil and are able to reach the plant’s roots.  Don’t fertilize in late summer as the hedge needs to prepare to go dormant for the winter.  In late fall you can fertilize with slow release nitrogen and phosphorus, which will lend the hedge a boost come spring.

Experts often recommend bone and blood meal as an alternative to another fertilizer formulation, so it is possible that the addition of a fertilizer for acid loving plants has resulted in some over-fertilization of your hedge.  For more detailed information on how to fertilize, take aSh look at an earlier Q&A posted on our website, “Fertilizing cedar hedges“, which provides practical information for you.

Emerald cedars can be vulnerable to such insect pests as aphids and spider mites, and these do cause browning and death of foliage, but unless you are certain that this is occurring, the application of insecticides is not necessary; indeed, often light insect infestations can be removed with a strong spray of water, or with insecticidal soap.  Here is some information on identification of and treatment for mites from another Toronto Master Garden post:  http://www.torontomastergardeners.ca/askagardener/newly-planted-emerald-cedar-tree-turning-brown-from-the-outside/

It will not be much consolation to know that you are not the only homeowner to experience problems with Emerald Cedar hedging.  Although it is a popular and reasonably priced alternative for hedging, these plants can experience stress on transplanting, and can be vulnerable to a few insect pests and diseases, as well as to extremes such as cold drying winters and drought in summer.  If you bought your trees at a reputable nursery, they should be guaranteed for a year, and you should be able to return them.

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 “emerald”, you will find several other posts answering questions on Emerald Cedars on a variety of topics.