A member of the cypress family, Thuja occidentalis, or American arbor vitae, is a pyramidally shaped shrub that can grow 40 feet tall. Hardy in U.S. Department of Agriculture planting zones 3 through 8, healthy Thuja occidentalis specimens bear dark-green evergreen foliage that gives way to clusters of cones that mature in autumn. Thuja occidentalis prefers moist, well-drained soil with a pH between 6.0 and 8.0. Ideal planting locations receive full to partial sun.
Break up the soil in the planting location to an 18-inch depth, using a garden fork. Test the pH of the soil with a soil-testing kit.
Amend the soil in the planting location if the pH is not within the proper range for your thuja. Add lime to the soil if the pH is below 6.0; add peat moss if the pH is above 8.0. Apply the amount recommended on the product label.
Dig a hole for the Thuja occidentalis, equal to the depth of its nursery container and twice its width. If planting more than one thuja, space the holes three to four feet apart.
Remove the thuja from its nursery container. Set it in the centre of the planting hole. Fill the hole with water from a garden hose. Backfill the hole with soil and pat the soil gently to remove trapped air.
Maintain moist soil with a garden or soaker hose to a depth of 1 inch during the first growing season. Water weekly at a rate of 1 inch per week. In drier weather, your plant may require watering twice a week. Once established, Thuja occidentalis will require supplemental watering only during drought.
Feed your thuja with an all-purpose fertiliser, following the label instructions for amounts and frequency. Fertilise the thuja in the early spring before new growth develops.
Soil-testing kits can be purchased at garden centres. Although it is not necessary its health, Thuja occidentalis can benefit from an annual shearing to tidy up overgrown branches. Use a pruning tool to shorten branches and maintain a pyramidal shape.
Do not overwater Thuja occidentalis. If the soil feels moist at a 1-inch depth, do not add more water.