I have a walnut tree that a squirrel planted in my yard and I put in the garden ("temporarily"). It's 3 years later now, and I would like to move it, but not sure if it's possible to have it survive. It is about 6 to 7' tall, and about 2.5" across on the bottom of the trunk. How do I know how deep the tap root is? Thank you for your time.

The challenge with moving a large sapling that is well established is the root damage that comes with moving the tree is very stressful to the tree. It can be done, but requires some work and the root ball that needs to be moved with it is quite large and will weight a few hundred pounds.

Only transplant large saplings in the dormant season (late fall through very early spring) after the leaves have fallen and before the buds start swelling, but you would want to prune the roots well in advance to a manageable size well in advance. For example, if you are going to move the tree this fall, you would want to go ahead and prune the roots back now. For a 2.5" sapling, you would want to prune the roots back to within 3 feet of the trunk.

In the fall after leaf drop or in the spring before bud swell, dig up the tree leaving a root ball 3 feet wide and a couple feet deep. Keep the transplanted tree watered and add mulch. There is no guarantee that it will survive, but the large the root ball that is moved with it, the better chance of success.