If you have the ability to do so in terms of budget and space available, you can make your own compost at home for simplicity in terms of getting a more regular supply, and controlling what goes into it. Our How to Make Compost at Home web page may be useful for getting started, and your local county Extension office might know of low-cost compost bins or other supplies to try. Soil is not the same as compost, as soil is composed of materials not found in compost, but topsoil can be purchased in bulk as well as bagged from a variety of sources, and bulk materials will be cheaper, if more challenging to transport and move about the yard. Topsoil is not regulated in Maryland, so you can inquire with the seller as to its quality (such as viewing soil test results) before buying. Soil testing doesn't work on compost (in that case, testing is specific to compost and may cost more), so they aren't interchangeable, but testing soil at home can also let you know what nutrient content it has, what acidity level (pH) it has, and how much organic matter is in it.

True soil, which is comprised of sand, silt, or clay (or a mix of those), can be too heavy for container use, both literally and figuratively, as it can hold too much moisture and not drain as well as pots generally need to. Therefore, depending on what was in a raised bed soil mix used in the bed you describe, the material may or may not be as useful for filling containers, though you could try diluting it with either potting mix or a drainage-improving additive like perlite.

You can re-use potting mix in containers from one year to the next, but will need to both add to it over time (as the mix compresses as it degrades, sinking further below the pot rim) and amend it to keep the drainage satisfactory, as compressed mix holds more water and less air in the pores between the particles. Roots need a certain amount of aeration to thrive and resist root rot infection. If you have your own compost pile, you can compost used potting mix as an alternative, which if the composting process is hot enough, can kill pathogens and pests. Overwintering pests inside the pot's used soil isn't as much of an issue as overwintering disease spores, though both are possible. If the plants succumbed to some of the common tomato diseases, such as a type of wilt, then replacing the substrate with new mix and giving the empty pot a wash-out with soapy water would be advisable. Our Growing Media (Potting Soil) for Containers page has more information.

Municipal landfills that collect yard waste (fallen leaves, branches, lawn clippings) from residents might give away or sell at a cheaper-than-retail price the finished compost they produce from that material, so you could check to see if that's an option in your area. Local Master Gardeners might also have ideas for sourcing materials at less expense.

Miri