I would like to grow these in a planter box (6feet long x 1 foot wide x 1 foot deep) , I only want them to grow 12\" to 18\" high , if I trim them at the desired height will the roots outgrow the box.
Goldcrest Wilma Conifers
Certified GKH Gardening Expert
The short answer is, yes, but if you are very familiar with keeping bonzai trees then this can be done. The roots will require constant maintenance, and trimming... But very properly. These trees are about 30 feet tall in nature, so keeping them 1/30th of that height will be very difficult. They also don't trim as well as their close relative, the Leyland Cypress. I would suggest crawling junipers. They will be more tolerant of confined spaces, and often won't exceed 2 feet in height.