Thinning Cedar Hedge

(Question)

Hello. I have a cedar hedge that is probably quite old.  We’ve had the house for 7 years and it was mature then.  It has become quite wide but the problem is, it is thinning.  It is what gives us privacy in our side yard from the street so it is very valuable to us.  Each year the hedge is thinning.  It was lovely and thick when we moved in.  I have used Jobe’s cedar hedge spikes before but saw no improvement.  When we had a drought a couple of summers’s ago we watered it.  We prune it annually.  I leave the fallen sugar maple leafs around it’s base as a mulch all year.  I’m wondering if that is making the soil too acidic.  The hedge is beside trees – Sugar Maples, Red Maple, Basswood and Butternut Hickory are all within a few feet.  We have probably about 70 ft of hedge along the front of our property then it goes back 45 ft on the side then more along the back.  I’m looking at possibly removing the leaves, adding manure and new soil and watering.  What do you think?  Thank you for your help.

(Answer)

The most common cedar planted in Toronto and Southern Ontario is the Eastern White cedar (Thuja occidentalis), which is native to Ontario.  They tend to grow in moist conditions and are often the dominant species when found adjacent to rivers.  There are several cultivars of this tree including Emerald cedar (T. occidentalis ‘Smaragd’) and Pyramid ‘Fastigiata’ which are commonly used as hedging cedars.  These latter trees are denser than the straight native tree and therefore with yearly shearing and regular watering, can be a long standing hedge.  The native cedar, which I suspect you have, are planted because they are inexpensive, easy to obtain and grow fairly fast.  With regular watering, feeding, mulching and shearing, this tree will be a little more open than the cultivars, but can be maintained as a hedge.

As you’d noted, your hedge was mature when you purchased the property.  You noted feeding it and pruning it yearly.  I don’t know exactly what you mean by pruning, but cedar hedges can be sheared any time of the year – this means using a hedge shear and removing some of the new growth to thicken the lateral buds.  If the hedge has been neglected, Mark Cullen recommends up to a third of new growth can be sheared off to encourage the lateral branching.  Cutting beyond the new growth to bare stems will not improve this.  No lateral budding will grow beyond the bare branch – hence, a hole.

Mark Cullen cedar article link for further reading: https://mark-cullen.blogspot.ca/2010/09/cedar-hedges-investment-that-grows.html

Cedars naturally grow in wet ground.  Regular watering is a must, especially in drought conditions.  Watering must be deep so a light sprinkling on the top of the soil is of no use.  Mulching is important to hold that water in the root zone, deter weeds and shade the roots.  Perhaps the maple leaves close by are too dense and water slides off and dosen’t reach the cedars.  Acidic soil should not be an issue, as evergreen cedars tend to acidify the soil around them.  If you want to use leaves as a mulch around the hedge, shredding them first allows more air space and more water penetration to the root zone.

Feeding regularly is important as well.  I am not sure the spikes are your best choice as they need water in order to disolve, allowing the food into the soil and without regular watering, this won’t happen.  In fact, a fertilizer that can be dissolved in water and applied directly to the root area will allow more of the nutrients to reach them.  Topdressing with sheep manure compost or regular compost will not only feed the hedge but will also improve soil structure, encourage beneficial macro & micro organisms and the earthworms will love you forever.

Finally, you noted that the neighbouring trees are very close.  Trees in general, are greedy for water and nutrients.  Those trees, as they have matured, have very large root zones and do not stop at property lines.  They will absorb as much water and as many nutrients as they can to the detriment of the cedars.  As well, they have matured in the last seven years too so they may be shading your hedge more than before.  Less sunlight means your cedar hedge has less ability to photosynthesize and make food for active growth.  Perhaps some pruning of these neighbouring trees to open up the canopies or to raise the crowns would be beneficial too.

So, to help save your large hedge – water regularly to combat the nearby trees need for water, topdress with some form of compost, mulch with shredded leaves, shear in the spring as new growth happens and prune nearby trees.  If you still feel the need to fertilize the hedge, use a water soluble fertilizer which will reach the root zone quickly.

Good luck.