Gypsy, Technically yes you can. But before you plunge into this project please research your plant's behaviour carefully. Most thuja's lend themselves well to such prunning, but I've known them not to regrow new leaves where it has been very hardpruned. So do be careful when approaching this project. Do things very gradually. Limit your pruning to the greenleaves only. Don't remove any central trunks, otherwise whatever space may be exposed will remain 'open'. No new growth will cover up that area. You can do a spiral with multiple trunks by simply treating all the trunks as if they were one. It would help too if you had a visual guide to assist you in this project like having a picture of a spiral tree. And also use a very visible and weighty cord to guide your pruning. Good luck.

Ianna

Thank you, Ianna - I will let you know of my results!

Pruning arborvitae in the landscape is seldom required due to their dense growth habit; however, they can be pruned at any time, with early spring being preferable. Winter browning can be expected with most species and cultivars. For this reason, arborvitae is not as highly recommended.

On that last note I had a neighbor that firecely pruned the growth of her two arborvitae, early each spring. Amazingly, they did survive the brutal attack, as I cringed to see the trees so severly pruned but growth was rapid to fill in.

Winter browning can be reduced by using burlaps to protect it against the winter's frost and wind. While cutting the leaves may leave brown spots, it's not lasting and if it is a bother, simply pull off that bit, so there's no cuts that are visible. A bit tedious perhaps but if it is a bother....well that's a solution.

It's always good to be cautious about which type of thuja you have before you plunge into hardpruning. As in bonsai you don't just take off main limbs and hope that it will come back the same way. It won't and it will be difficult to undo any mistakes. In the case of multiple trunks, an outer trunk may be supporting branches and leaves that makes the tree look dense. Work slowly and gradually by first using the spriral cord as a guide. With very sharp pruners, follow the guide forming a very visible 'line' and then cut deeper and deeper until you can expose the trunk/trunks. Finally, if you are satisfied with the 'line' you can expand it by exposing more of the trunk, and then gradually shaping the plant making other parts more rounded. Now the more the plant gets sun exposure, the more the leaves are encouraged to grow. Every now and then you will need to prune the leaves back to shape. That will encourage the plant to produce even more leaves. Remember that when there's not sun exposure, there will be no leaf growth.

Thujas are great for topiaries. A good candidate is the Emerald cedar.