I have read in several sources to use the diameter of the tree's trunk to determine the size of the root ball to dig up when transplanting. I have a clump of birch trees I want to attempt to transplant. Do I use the largest trunk or do I add the trunk diameters up?

The clump consists of three trunks, 2" + 2" + 3" diameters.

  • 1
    The question reads like you want to transplant the entire clump en masse. Is this correct? If so, then (roughly) how big is the clump?
    – Jurp
    Jul 8, 2022 at 13:49
  • Wait until dormant and move them bare root. I friend worked for a golf course and moved trees occasionally. Every tree he moved had the same size root ball - One backhoe bucket. Jul 8, 2022 at 14:42
  • I added the diameters of the trunks. I do want to move the clump together. I have until this fall so I plan on severing the roots with a spade shovel and watering well to get feeder roots to establish before the backhoe picks the root ball up. We are moving it as a result of a room addition. 8 year old Royal Frost Birch.
    – Evil Elf
    Jul 8, 2022 at 17:57
  • @blacksmith37 How big of trees and how big of a backhoe bucket?
    – Evil Elf
    Jul 8, 2022 at 20:54
  • 2
    Given "construction schedule" and wanting to save the trees, MIGHT be worth getting a quote to have a tree spade in for (probably) an hour. Takes a considerably bigger bite than a backhoe, and drops the tree(s) right into a perfectly fit hole. A specialist tool, but some specialist near you has one, probably. More often used to move larger trees, but this is effectively a larger tree in many ways. More like a plug than a ball...significantly less stress on the tree(s).
    – Ecnerwal
    Jul 8, 2022 at 23:00

1 Answer 1


According to this excellent page from Iowa State University, you need a 24" root ball for a 2" caliper tree and a 32" root ball for a 3" caliper tree (see that page for a handy chart, and note that it states that the "caliper of the trunk [is] measured 6 inches above the ground up to and including 4 inch size").

In order to best calculate the diameter of the ball you'll need to make, you should measure each tree separately. It's easiest if you make a chart something like this:

enter image description here

As you can see, I measured each tree's suggested diameter separately, combined them to come up with a common width, then subtracted the amount of overlap between the two diameters. In my example, I'd need a 48" root ball, centered between the trees. Assuming your trees are spaced closer together than those in my drawing, you're probably looking at an approximately 40" root ball, although I'd definitely do the exercise as shown in my sample to get a better figure. Of course, as blacksmith noted in their comment, the width of a root ball is often the width of the backhoe's bucket.

Note also that the site I link too strongly recommends only moving trees when they are dormant.

  • On the dormant front, I don't have a choice. We can trash it, or give it the ol' college try.
    – Evil Elf
    Jul 8, 2022 at 20:56
  • Ah, you're up against a construction schedule... All I can recommend then is to water, water, water, and prune some of the younger branches (you'll know which ones - they'll wilt). I hope that you don't have too-high temps are a drought after you move the trees. :)
    – Jurp
    Jul 8, 2022 at 22:53
  • It will be in fall. Maybe when it's dormant.
    – Evil Elf
    Jul 9, 2022 at 22:16

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