If your soil is like most, it’s more suitable for creating a clay-fired pot rather than growing plants. One way I get around this problem is that whenever I put in a new plant, I remove the old soil with a bulb planter and replace it with my new soil mixture. Here’s my recipe:
5 gal bucket of compressed dried peat moss.
1/2 – 5 gal bucket bucket of old soil dug out of the old holes.
1 bag 40# potting soil – don’t just buy cheap top soil. I pay $2 for a 40# bag from Home Depot or Lowes.
2 large chunks of natural charcoal, pulverized by a brick.
1 handful of 10-10-10 fertilizer.
Note – if you’ve got lots of extra cash, the pros use “Turface” as an amendment also.
I’ve tried it out, but was not impressed for what it costs.