Potting soil for containers
Growing plants in containers requires much different soil than growing plants in the ground. It is important that you do not use garden soil for container gardens.
Using soil from the ground or bagged garden or top soil can cause all kinds of problems when used in a container. The biggest problem with garden soil is that it is so darn heavy. Many years ago, before I had any experience with container gardening, I used garden soil in a window box. It held up for a couple years then ripped right off the house and fell to the ground. What a mess. So what makes some of the wonderful things that are good for your garden bad for your containers?
Bagged garden soil is full of cheap additives that make it heavy but provide a good texture mix for ground gardens.
Bagged garden soil and ground soil do not drain as well as potting mix.
Composted manure is full of nitrogen but the concentration is too high for a container.
Homemade compost generates all kinds of bacteria and fungi that aid the decomposition. But when introduced to a “clean” pot with no soil predators, they can go to work on plant roots.
Ground soil tends to be fine particles and can become very compacted. And there are no soil critters like earthworms to keep it aerated. Air is important to roots and air pockets help to retain water.
With all that said, a lightweight peat enriched bagged garden soil (not topsoil) will probably work ok for some plants grown in a container IF you care for it appropriately. Plants that enjoy wet soil would do best. But, why make life difficult? Just buy or make a good container mix.
Advantages of a good potting mix:
Formulated to hold water and drain any excess.
Soil particles are typically large and fairly uniform, which aids in aeration and prevents compaction. This also aids in draining off excess moisture. A good mix will contain peat moss, pine bark, and perlite (or vermiculite).
Potting Mix is lightweight, making it much easier to move your containers.
While we are on the subject of what to put in your containers, there are a couple of things I would suggest you never put in your containers
Sand - it is not a good growing medium and will do absolutely nothing to improve soil or improve drainage.
Rocks - will not improve drainage and will only make your container heavy. Excess moisture will not move easily from soil to air spaces. Water will slowly drag soil down into the rocks to fill the spaces, quickly negated what you THOUGHT you were accomplishing.
Empty plastic bottles - or anything else you may put in the bottom to take up space so your container is not so heavy. Why on earth would you want to deprive your plants of the one thing they love best, lots and lots of soil to spread roots in. If you are absolutely convinced that your plants don’t want the extra soil, you need a smaller container