The proper method would be "cook" or steam treat (not an option for many people) the soil to deal with possible pathogens + weed seeds...but most people don't bother, cross their fingers, and reuse the soil after adding a little bit of fresh peat or coir + perlite or vermiculite.

Ultimately, it's weighed on how important what you're growing depends on you being able to grow/harvest vs how much risk you're willing to take. The risk is quite low, but for some people that's too much of a risk.

Don't reuse any container soil from known disease-carrying plants...at least without treating. Some people scrape the first 0.5 to 1 inch of soil and discard it in order to keep weed seed pressure down on reused soil. Don't reuse soil you grew root spread crops (like mint) in. As an alternative, a lot of people throw it into their compost pile for ground soil additions and if properly composted it takes care of most of the negative aspects associated with the used container soil.

Perlite is a mineral, volcanic glass one source describes it, so it should not need to be replaced although if compost is added to that potting soil more perlite might be needed. The link below is about reusing potting soil.

Here is a link that might be useful: reusing potting soil

Thanks, that is what I needed to know! It would be soil from pots containing hot peppers/tomatoes and a couple with beans. A couple hours work seems much more preferable than dropping another $200 on potting soil.

Much appreciated!

Whether or not potting soil can or should be reused is open for some discussion. First, it depends a lot on whether or not the plants in that container previously were healthy. If not, many diseases can be carried over in the soil and it is just not practical (nor pleasant) to sterilize any sort of quantity of potting soil. If you do reuse the soil, I would not recommend replanting with peppers and tomatoes again regardless of any disease issues - the theory of rotation applies to container grown plants just as well as inground plants.

Second, reuse also depends on the quality of the soil to begin with. A great many packaged container soils (like MG) are simply not very durable - they breakdown during the growing season and being of too small and too uniform particle size to begin with, they compact and drainage and aeration are seriously compromised for continued use.

If you DO decide to reuse potting soil, you do not want to add compost, peat, vermiculite or anything else that will compact when saturated or will continue to decompose. Add bark fines, Turface or perlite/pumice to provide durability and adequate drainage.

This subject has been discussed ad nauseum on the Container Gardening forum. Good quality durable, fast draining potting soil is the key to the success of container gardening.