Well prepared garden soil is great for growing things in the ground but when it comes to growing things in containers the soil is different.
Soils for containers need to be well aerated and well drained while still being able to retain enough moisture for plant growth. So when choosing what to use to fill containers, never use garden soil by itself.
Container soils are often referred to as soilless or artificial media, because they contain no soil at all, often composed of peat, vermiculite, bark, coir fiberin a variety of recipes depending on the type of plant being grown. Succulents, herbs, and perennials tend to prefer well drained soils, media that are coarser in texture containing more bark, perlite or sand. For tropicals and foliage plants, more peat and finer material as these plants tend to prefer moisture growing conditions.
Garden soil needs to be modified or amended. An acceptable soil based mix can be made by using one part garden soil, one part peat moss and one part perlite or coarse builders sand.
Over the course of time, the organic materials that the soilless media is made from break down and decompose to the point where you will loose the drainage and aeration properties that are inherent in soilless container medias. When that happens, discard the media to the compost pile or to the garden and refill the container with fresh media.
When filling containers with media, don’t fill the pot to the top. Leave about a one inch space between the top of the soil and rim of the pot. This will help make watering the pot easier as it provides a place to “put water” and not have it run over the edge.
Filling very large containers can be costly especially when using commercially prepared media. To reduce the cost and also the weight of the container consider adding “filler” to the bottom of the container with something that is inert, able to take up space and not break down over the course of the growing season. Items such as crushed aluminum cans, plastic milk jugs, and non-biodegradable “packing peanuts” are usually readily available. Lay a piece of landscape fabric over the top of the material and fill the rest of the container with media.
This is an autogenerated summary from a published source: Using Soil and Soil Mixes