Shade garden beside cedar hedge


Hello. My climate zone is 6. My soil is sandy loam but part of this garden is over a hard pan. A well drilled nearby informed us of that, along with planting some trees and shrubs 15 years ago. A row of Holmstrup cedars run in an east west line providing shade from the south sun on the affected bed just north of it. There are also 2 silver leaf linden trees that my husband has kept trimmed and thinned out. Therefore there are lots of roots from one tree over the hard pan area that have grown up 4-6 inches out of the ground.
Last year we built up the area with 4-6 inches of soil around the tree roots and placed several stepping stones with gaps left for ground cover, of which several have survived the winter.
However, last fall several plants in the 3-4 foot wide bed directly beside the hedge died. I had some hostas, some astilbes, Japanese grass that didn’t look too healthy and the impatiens developed a rotting disease along with the begonias. We have an irrigation system. There is some filtered sun getting through the trees at various times of the day.
The hedge is also turning brown on the north side(our side) but is nice and green on the south side.
Any advice would be greatly appreciated since we will be spending more time in our back yard this year

Could this be a soil problem? Can you suggest where to get a soil test done in a rural small town area. I live in Simcoe near Lake Erie-not north of Toronto. I am wondering if the soil is too acid but I thought cedars like an acid soil. I was also wondering if it is a root problem. I did fertilize with a slow release granular flower/shrub fertilizer.
Thanks in advance for any help. Cindy


A soil test is a good idea. It will tell you how healthy your soil is now or what nutrients may be lacking. Here is a link to a previous question on our site that gives good information on where to get your soil tested. You can also get a soil test done at the University of Guelph laboratory. Follow their link to see how to submit soil samples. Note that although cedars like an acidic soil, one that is too acid can cause browning.

The concurrent browning of the cedars and die back of some perennials suggests a common cause especially as this is a well established cedar hedge and the damage just occurred over the past year. Thuja occidentalis ‘ Holmstrup’ (Eastern White Cedar) do not tolerate dry or drought conditions. I noticed that you have an irrigation system. It would be a good idea to periodically check the moisture in the soil to see if there is enough water being distributed or too much. You can purchase a simple water meter probe from many nurseries or on line. Keep in mind that a good soaking is better than frequent light watering to ensure that the water gets down to the roots of the trees. During the winter evergreens can suffer from winter burn if exposed to winter winds which desiccate the needles. A good watering in the fall before the ground freezes helps to prevent this from occurring.

Something else to keep in mind is a natural process common to some cedars. In the brochure link included below, the authors point out that:

“Cedar Flagging/Browning (Environmental): Foliage takes on an overall brownish or purplish colour in early spring. This colour may change rapidly. Healthy plants will green-up as the season progresses. It is very common on Western Red Cedar and less frequent on Eastern White Cedar. Flagging may be more severe in hot, dry weather but is not harmful to the tree.”

With regard to your perennials that died, you didn’t indicate whether they were established or newly planted when the soil was added. Both the hostas and astilbes can thrive in filtered sun but I am wonder again if they were getting enough water to their roots or maybe too much, as either condition can kill a plant. Getting a soil test and checking your water efficiency may also solve this problem.