(Suggested by a 'basil problem ' post)
Why does dirt sink in a pot? I *expect* a certain amount of settling and compaction over the first year, but I've seen the soil level in plastic pots sink and sink year after year. I know plants use soil nutrients, but surely that would be a tiny amount in terms of volume. Even 'erosion' through water draining can't be *that* much, can it? A large plastic pot had sage in it for about 5 years. Finally, the sage became woody and unproductive and I started some new plants. When I drug out the pot from surrounding foliage, the soil level was about halfway down the pot! What's going on?