In the short term after potting up, your plant is most likely going to look fine.
However, after a few weeks or months, some signs that the plant is not happy can begin to show. Watch for;
- Leaf yellowing
- Leaf browning
- Leaf fall
- Stunted growth
- Bronzing on evergreen such as box plants and yew
- Soggy compost on the surface of the pot
The reason the plant is showing signs of stress is because the large volume of new compost that was added when it was potted up is sitting wet for a long period, reducing aeration around the roots. Instead of the roots growing out into the new compost, they simply rot. Plants in the ground do not suffer the same fate as the soil is inherently better drained than compost in pots.
Although the compost will dry naturally through evaporation, it takes longer when there is a greater proportion of compost to roots. The more fresh compost there is, the more it will stay wet, creating a soggy ring around the rootball. Finer growing medias that hold onto more water are particularly prone.
Plants that show some of the symptoms described above are often mistakenly watered more not less, thus adding to the problem. And if the overpotting was done late in the growing season (after June), rather than in spring, this too will mean it is exacerbated by slow plant growth and wetter conditions.