We don't replace soil in raised beds because we have the earth below creating movement of water and air in the soil.

Raised beds are earth based gardens. Containers are completely disconnected from the earth by virtue of being containerized.

The concept that I want you to understand is this: Water doesn't move unless air does. A simple example is a drinking straw in a glass of water. Dip it in and place a finger over the top of the straw. Withdraw the straw and the water doesn't move out of the straw. Remove the finger and the water runs out because now air can enter.

In the earth water is constantly moving through the soil and therefore so is air (the earth has no drainage hole where the water exits the system).

In a container the water runs down and out the drainage hole and then water movement stops and therefore so does air movement.

This is why containers and the earth are so different.

In a container we need a coarse mix that allows the free movement of air and water (drains well). In the earth we can get by with tighter soils because water still moves and thus air still moves.

A potting mix is only as good as it's particle size. If you purchase a store bought mix it will probably be just fine in the first year, but the organic part of the mix gets broken down by biological activity and weathering. As it is broken down it breaks into smaller and smaller particle sizes and before long the smallest particles which wash to the bottom of the container are getting closer and closer to having clay soil in the container. This holds a lot of water and very little air which plants need.

Miracle Grow soil is peat based and peat based soils are generally good for one season and sometimes 2 if they aren't exposed to the elements any longer than necessary. After that they are so collapsed/broken down that they will have an adverse affect on plant performance and should be dumped out into the earth based garden and replaced.

For more info, please visit the container gardening forum.

Well... I don't replace my garden soil every year even though the I take from it at each harvest. But I do put back, in the form of compost and other organic fertilizers. I would think you could do the same with your potting mix. I doubt it would ever stop draining, but if it did, you would at least then know it needed replacing.

Adding at least some new planting mix to your containers will help replace nutrients last year's crops used.
Renewing the soil each year is one way to renew the nutrients in the soil available to plants. Adding aged compost to garden beds adds a wide range of nutrients that feeding plants have extracted from the soil. The same goes for soil in containers.

Also, you would not want to use a second year soil that was host to a diseased or pest ridden plant. That soil is best disposed of.

Here is a link that might be useful: HarvestToTable.com

I actually reuse 25% of my soil from last years container grows, and recycle the other 75% into the garden. The 25% that is reused is added to my totes of organic enhanced soil in chunks-roots and all-and in a couple weeks, you cannot find any signs of the stems or rootballs left. I have a very active soil. All this said, I have reused my soil in moderation as I have many long lasting organic nutrients that will continue to break down over many years. If trying to reuse for any other reason, I would use it to increase org matter into garden or yard or compost pile.

Good luck TiMo

I've had a few house plants that don't make it, esp annuals. I dump the whole thing in the compost pile and clean the pot w/ water and then hydrogen peroxide then rinse w/ water again. I'm certain that any soil borne disease will be taken care of w/ hot composting and gets resused in the raised beds.

You can absolutely re-use that potting mix, but you will have to replenish it first. Mix in a big scoop of good compost, and if it still feels like it has compacted and has lost its ability to drain well, you can add a bit of perlite to improve drainage.