Thinning cedars


Hi, I live in Montréal and I noticed that my cedar hedge is thinning. The cedars are 30 years and they are swamp cedars e.g. the cheapest trees available. The cedars are now 20 – 25 feet high. Should I face them, if so, how much? Should they be watered every week, what fertizer brand should I use and how often should it be applied? Thanks,


Thank-you for contacting Toronto Master Gardeners (TMG) with your question about your cedar hedge. Swamp cedar (Thuja occidentalis), also known as Eastern White Cedar is a popular hedging choice. We get numerous questions on planting and maintaining these hedges. I have included links below to a couple of our previous responses. You can also search on the TMG website for additional information.

As the name suggests, Swamp cedars prefer a moist environment but they are also susceptible to root rot so giving them the right amount of water is key. The amount and frequency of watering will depend on your soil and environment.  The general recommendation is the ensure that the soil remains moist at 6 inches below the surface. Adding a mulch of wood chips or bark around (but not touching) the trunks can help in keeping a consistent moisture level and reduce the need to water.

Older cedars can profit from fertilizing. You could purchase a commercially available fertilizer, but TMG does not recommend specific brands. An alternative would be to apply compost, well rotted manure or leaf mold.

Pruning is an important component in maintaining a healthy hedge. It is good to begin this process early, but even with your tall, older hedge it can help in producing new growth. Keep in mind that you cannot cut into brown areas. New growth is generated only on the green parts of branches.  Tipping the tops of the cedars has the additional benefit of allowing more light into the plants’ interiors and to the lower branches. Some of the thinning can be caused by a lack of light. The rule of thumb on pruning is never to remove more than a third of the foliage or a quarter of the height in one season. Better to prune lightly the first time and go at it again next year. The best time to prune is late winter/early spring before growth begins. If you prune at all this year, keep it to a very light prune.

This link will lead you to a previous Toronto Master Gardeners response on watering a cedar hedge. This additional TMG response gives good information and maintaining an older cedar hedge: TMG on maintaining an older cedar hedge

I hope this information assists in maintaining your hedge.