Next spring, I plan to buy a number of Emerald Cedars. Other than cost and place of origin (USA vs Canada), is there any difference between those purchased at a local big box store and those from a local nursery?
Also, do all growers intentionally clip the leader stem at any early stage to encourage a bushier appearance?
You are correct in thinking that plants in different retail centres may have different origins in terms of where they were grown. In addition, they may have different origins from the point of view of HOW they were grown. Trees and shrubs can be field grown or container grown, which is to say grown out in a growing field and then dug up and sold bare root or transferred to a container for sale, versus those that are started as seedlings, cuttings, cutting or grafts and grown on in a container of potting soil until ready to be sold. Often, the latter will have roots poking out the bottom of the container. If field grown near your location, you will know that the trees are acclimatized to your local conditions, where container-grown or containerized bare root plants may have come from a different climate.
We have no way of knowing whether all growers ‘head back” their cedars. Usually, the Emerald Cedar (Thujaoccidentalis “Emerald Green” or “Smaragd”) will grow into a natural pyramidal shape without pruning. Please be aware that they want to grow to be as much as 15 feet tall and 3-4 feet wide, so bear that in mind when planning your planting.