Red Tip Photinia

It will grow quite fast to 10-15 ft. I used to have Photinia and was constantly trimming it because of its fast growth.

Okay, but the question was what is the largest size you can buy it initially and hope to get healthy plants that are not root bound?

For a plant that grows that fast, I buy the smallest size (1 gallon), not the largest. In many cases, you won't know the difference after 3-4 years. With Photinia, you won't know the difference after 1-2 years.

Why would it be your goal to buy the smallest plant? Only because it is the cheapest?

Why wouldn't you want to get the hedge to full size faster, if cost were not the issue?

Because it is likely to be healthy and not rootbound.

Because the biggest doesn't necessarily get there first. If the biggest is not healthy and particularly if it is well rootbound the smallest may overtake it and do better in the long run.

David (the other one)

For Photinia Red TIp in particular, is it difficult to find healthy 6 ft hedges in 15 gallons planters? I understand root-bound plants are bad.

You (the other David) are quite correct. Furthermore, smaller plants seem to get extablished better, are easier to plant (smaller holes), and

-- yes -- are cheaper that larger plants.

The key to getting established is for roots to grow into the native (but improved) soil before the foliage grows. The larger plants -- even those that are not rootbound -- tend to have too much foliage relative to the size of the root ball.

Good gardening practices require patience.