How do you identify quality? Read the label for quality ingredients such as sphagnum peat moss (not sedge peat), aged bark (or composted forest products), perlite, vermiculite, lime, and a wetting agent (which helps soil stay uniformly moist). Other ingredients might be gypsum, peat humus, and compost. Optional ingredients include moisture-holding polymer and fertilizer. A few even include pesticides—avoid those for vegetables and herbs. Products labeled "bagged topsoil" and "compost" are cheaper, but reserve them for working into the ground or raised beds, not for pots. In a pot, where watering happens often and plant roots need to fill the container, you need a lighter medium.
We want you to use the best soil possible, because good soil and good plants from Bonnie are key ingredients of successful gardens.
One way to test a potting mix or soil is to see how it drains. When soil is placed in a pot and watered, the water should start draining out within five to ten seconds. If the soil becomes soupy or water drips out slowly, it doesn't have the right balance.