Yellowing Emerald Cedars

(Question)

I planted emerald cedars last year and this spring/late winter they started turning light green, then yellow and browning at the bottom. They were planted with topsoil and mulched and I’m watering them.  What is wrong?

(Answer)

Yellowing and browning of cedars at the bottom indicates that the roots may not have grown sufficiently after they cedars were put in.  There are several reasons why this may have happened.

  • Cedars thrive on moisture and nutrient-rich soil.  There may have been some moisture deficiency after they were planted and before the ground was frozen.  Either watering wasn’t sufficient to encourage strong root growth last season or the roots in the root ball were not separated (teased out) before planting and have not been able to penetrate into the surrounding soil. Watering deeply and thoroughly (at least once or twice a week after planting) is key so that the roots can take hold and spread.  This can be done easily by using a soaker hose along the base of the cedars for several hours.  Watering should continue well into the autumn until the ground is frozen to maintain adequate moisture through the winter.  The cold winter winds can desiccate the foliage – once the ground is frozen, the tree cannot take up moisture to replace what is lost from the needles/leaves.
  • What type of soil do you have?  If you have clay soil, roots may have difficulty growing into it, so adding organic matter may be helpful in adjusting the soil structure.  You may also want to check the root ball – if it is still intact or if you find the roots are girdled (growing around each other), you may need to find a way to tease the roots apart to encourage outward growth of new roots.  Make sure the soil around the root ball will allow the roots to penetrate into it so try not to excessively compact the soil during planting.
  • You mention that topsoil and mulch were used when the cedars were planted.  Compost, triple mix or manure might be better choices than topsoil when planting – not only do they contain more organic material, they provide more usable nutrients for the roots.  They can easily be added as topdressing on a annual basis to help improve soil structure and allow the soil to retain moisture.  The use of mulch is an excellent way to maintain moisture around the shallow root system of cedars – it also gradually adds nutrients to the soil as it decomposes and will also be beneficial in keeping weeds at bay.
  • Did you fertilize the trees after they were planted?  Excess fertilizer can cause root burn and prevent the roots from growing.
  • Also, this past winter (2015), here in Ontario was quite severe with long periods of frigid temperatures.  This is especially hard on evergreen plants as leaves or needles remain on the plant.

The fact that you are watering them now will hopefully encourage the roots to grow and since we’ve not had (in the Toronto area) a lot of moisture this spring, it will help the plants replace loss through transpiration.

For further information, please check out the Toronto Master Gardener website at the links below:

https://www.torontomastergardeners.ca/index.php/askagardener/emerald-green-cedar-turning-brown/

https://www.torontomastergardeners.ca/index.php/askagardener/cedar-trees-leaves-turning-brownyellow-after-sept-pruning/