Question: When transplanting a seedling shrub into a larger pot, can I skip the intermediate sizes and put it in the largest pot I have?
Answer: Moving a small plant into a large container is likely to cause two problems.
The first concerns watering. The large volume of soil can remain wet for long periods of time, leading to root rot.
Second, it is difficult to be sure that the young plant is receiving the right amount of fertilizer. Nutrients are likely to leach out of the pot before they can be absorbed by the roots.
So, when potting on, choose a pot that will leave just an inch or so of soil on all sides of the existing root ball.