Cedar hedging (Thuja plicata, and Thuja occidentalis) are a great option for quickly creating privacy in your garden.
You can plant cedars almost all-year round, although early spring and/or fall is preferred.
Cedars do best with a slight acid to neutral soil (pH of 6 to 6.5 or as high as 7.5). Soils that are too acidic can result in nutrient deficiency symptoms (browning or yellowing of foliage) and eventual tree decline. They also will struggle in water logged soils. So, make sure you have good soil with proper drainage. Cedars appreciate lots of water but don’t like wet feet.
It’s always a good idea to amend your soil when planting, but not too much. The best practice is to use a mixture of 2/3 soil from the planting hole, and 1/3 an organic amendment (such as Sea Soil™ or Compost). If the soil does not drain well, it has a high clay content or is hard packed, you may want to create a raised planting bed or at a minimum mount the planting area to try to create drainage conditions.
Plant cedars in full sun to partial shade. If cedars are planted under and an overhanging tree or between two houses, they will gradually decline, eventually becoming bare and dead. When planting cedars you should avoid times of very hot temperatures if possible, hot summer weather may cause the root ball to dry out during transport. It is best to plant these new hedges in cool weather to insure the roots stay moist. They will also require regular watering to make it through the first few summers since their root system is not full formed yet.
Dig a hole at least twice the size of the root ball and loosen the soil so the new roots can easily penetrate. This is also the perfect time to add amendments (see “Soil Preparation” above). Make sure the planting hole is no deeper than the soil level of the plant. Planting too deep will smother the roots and deprive them of oxygen.
Cedars are relatively shallow-rooted trees. This makes them susceptible to drought stress especially in sandy soils. The extremes of very wet conditions in the fall and winter, followed by a hot, dry summer, is very stressful for the roots. Hedges should be watered regularly during very dry periods.
Mulching is a great way to maintain even soil moisture and temperature, that will hopefully result in less watering needed. But keep in mind that prolonged flooding and over-watering can also cause root death from lack of soil oxygen. Water can accumulate under hedges that are planted downhill from watered lawns. Watering with sprinklers that are timed to go on at short intervals every day will keep the soil continually wet and promote shallow rooting, which is not desirable. The best practice is to water deeply for 30-40 minutes, 2 or 3 times per week.
There are some cases where physiological effects can happen even though all care has been taken to plant the hedge correctly. If only a few branches have died out in patches along the hedge in summer, this may be natural phenomenon of cedar trees called flagging. It is very common on Western red cedar (Thuja plicata). Flagging may be more severe in hot, dry weather but is not considered harmful to the tree. The foliage may take on a bronze to reddish brown to black colour in cold winters. This is natural and the trees will green up as the growing season progresses. A few varieties have a natural bronze or blue tinge in certain seasons.