We have two Degroot Cedars approx, 8 ft (2.4 m) high. Both are separating/splitting into two near the tops of both. Is there any way to prevent this other than tying the two parts together with string? I live in North York. Please see attached photos.
Thank you for contacting Toronto Master Gardeners.
Thuja occidentalis ‘Degroot’s spire” is a dwarf variety of Arborvitae. These slow growing evergreens typically grow to a height of 8 to 12 feet after 15-20 years. These require no or little pruning other than to remove dead or damaged branches. Any trimming should only be done to the level of green wood; if pruned into brown wood then no growth will happen from that branch. Trimming should be done in later winter or early spring, before new growth occurs.
Thuja have a central tallest upright branch at the top, called the leader. It is a little difficult to tell from the images, but it is possible that your tree has two stems (branching in the lower portion of the tree, of brown wood), each with a leader. If that is the case there is not much you can do to alter the growth shape. Alternatively, it is possible a single-stemmed tree developed two vertical leaders rather than one, or the leader may have been trimmed in the past into the brown wood, and two other branches have grown to become leaders. In that case you can remove the weaker leader in early spring, and make a splint for the remaining leader to make it grow more vertical. The splint and ties should be removed after about a year, and not be so tight that the branch is damaged. The reference below gives some information on growth of evergreen trees. The Toronto Master Gardener’s website also includes a guide “Evergreens Suitable for Hedging” that may be helpful. https://www.torontomastergardeners.ca/guidecategories/evergreens/