I'm running late to the party here, but I wanted to give you some info anyway~

When you're growing in pots you want good air and water movement. Plants breathe through their roots, and roots are very vulnerable to rot, so you don't want them sitting in gloppy and wet medium. People say all the time that it's ok to reuse old potting soil with organic matter in it, (like old roots) and up to a point, in general it's ok. Chances are the next plant won't be all that affected. But some particular plants will. Geraniums especially need light and quick drying potting mediums. As do rosemarys. But according to a scientific approach, using fresh potting medium is best for optimum growth, no matter what you've got in the pot.

The link I pasted at the bottom is really long and kinda dense, but it's valuable information concerning growing in containers, which is very different from growing straight into the ground. In pots there are different physical properties at work, specifically the pull of gravity versus the absorbency of the potting medium used. Those two forces create what's called a "Perched Water Table" in the pot. Which is a band of wetness that stays after the excess water drains out. Now if your roots are above that, that's good, that helps. But if it's not, your plant will suffocate or its roots will rot.

This info also addresses the "should I put something in the bottom of the pot for drainage?" question. The answer is: if the pot is tall, really tall, it should be ok. Use mulch, broken up sticks, or leaves - use some kind of organic material you can dump in your compost pile later. But if the pot is not tall, you will push the Perched Water Table up into the roots zone. Which you don't want. I generally like at least 12 inches of potting soil in my super big (16+ inches tall) pots.

Certain terra cotta pots are named for the plants that will do best in them. "Rose" pots. "Azalea" pots. Those are designed based on the PWT- rose pots are high and narrow, to keep their roots on the dry side. Azalea pots are low and squatty, because their roots like a bit of extra moisture.

Drainage is a function of particle size of the potting medium used. Big particles have big spaces in between them, so air and water flow easily and quickly. Small particles have smaller spaces, and air and water moves slower. And a mix of both large and small can be bad for any plant, because the small particles settle inside the spaces left between the big particles, and you've blocked up the channels where the air and water flow. (Imagine a square pan with 12 golf balls in it. Four rows of three balls in it. See the spaces? Then add some marbles. See how they fit in between the golf balls?) Which is why it's best not to add other stuff to commercial potting mixes, like sand or compost. You're running the risk of mixing particle sizes. And reducing air and water flow.

At any rate, read this! Good stuff!

https://www.houzz.com/discussions/1375349/container-soils-water-movement-and-retention-xviii

When I have dead containerplants I cut off the dead plant and put it in my compost and then I just dump the soil directly in the garden. I chop it up, so it's easier to distribute and to plant/sow in :) I'm sure you'll be fine. Just don't use soil from say container cucumbers where you want to plant cucumbers etc.

It might actually be better not to grind up the smaller roots and disturb the soil too much, because that can disturb the rhizomes that are so important for soil health. You can look up no-dig gardening to learn more. I'm honestly not sure how much no-dig gardeners do from year to year, but I think they minimize it for healthier soil.