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Temperature

Excessive heat in combination with drought can stunt leader development. 

 

Light

Plants should be grown outdoors in full sun, except for some yellow/variegated varieties which may require 30% shade. 

 

Crop Timing

Transplant in early spring to early summer, establishing roots before the summer heat sets in. Planting can also be done in later summer or early fall if roots are established before winter conditions set in. 

 

Media

Thuja must be grown in a media with adequate air porosity. A minimum of 40% coarse peat moss should be incorporated into the soil mix. Media pH must be kept between 5.0-6.0. A low rate of 8-9 month slow release fertilizer (18-6-12, for example) can be incorporated into the media.

 

Irrigation

Careful water management is important to ensure that the plants never dry out during the summer months. Drought stress will cause stunting of the growth and loss of plant vigor as well as causing shedding of the inner foliage and heavy cone set. 

 

Fertility

Maintain an EC of 0.7 in the pot (using the 1:2 dilution method). This can be done with liquid feed, slow release fertilizer or a combination of the two. If plants are held over the winter, top dress with a low rate of Osmocote 18-6-12 in early spring and again in mid summer. Combine this application with a topdress of magnesium sulphate, 14 grams for a #2 nursery container and 7 grams for a #1 nursery container.

 

Trim

Trimming depends on variety and end goal.  Most upright Thuja spp. simply need the growing  tips removed in the early spring. 

 

Space

Ensure that plants always have adequate space so as not to be touching each other. The foliage needs air flow and light to maintain color and shape. 

 

Pest Management

Thuja spp. has no serious disease problems. 

Common insect pests include: spider mites, Lepidoptera, and aphids.

Spider mite frequency can be reduced by irrigation systems such as overhead sprinklers that regularly wet plant foliage.