Potting Soil

You may be surprised to learn that potting soil is not really soil at all.


Potting soil, also known as potting mix and potting compost, has been used by gardeners since the 1800’s, and there are many good reasons for doing so. First, let’s find out what, exactly, is in potting soil.

Peppers growing in potting soil (Kate Russell)

Potting soil ingredients
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Potting soil is a manmade recipe often made out of composted bark, sand, perlite, peat, recycled mushroom compost, and mineral nutrients. These mixes are treated to create the best pH for plant growth. Some potting mixes contain slow-release fertilizers. You can find potting soil that is rated ‘organic’ according to OMRI regulations, and you can find potting mix that includes ground up old car tires. It’s one of those cases where you really do get what you pay for. If you are committed to organic gardening, be sure to look for the OMRI label.


Potting soil’s unique properties

Potting soil is designed to retain moisture and nutrients. [Because of this ability, fungus gnats are often attracted to pots filled with potting soil - it’s the moisture.] Potting soil is also sterilized to kill off pathogens and weed seeds. This is what makes it so useful in container gardening. Some potting soil mixes are designed for specific plant species, such as African violets or cactus. Fresh potting soil is also what keeps your window sill garden and holiday plants healthy and productive. Stale potting soil… not so much.


How to recondition potting soil

Old potting soil may not actually contain anything useful to your plants. Like garden soil, nutrients are ultimately depleted and must be replaced. Also, potting soil, in particular, becomes hydrophobic as it ages. This means that it actively repels water, allowing it to quickly drain out of the bottom of the contain, leaching valuable nutrients as it goes. You can either dump it out and buy new potting soil, or you can recondition what you have. To recondition old potting soil, simply top dress it with aged compost and water it in. No digging or repotting needed. Also, you can apply an attractive mulch of wood chips on top of your potting soil to act as a slow release of organic material and some nutrients.


Uses for potting soil
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Because of its ability to retain water and nutrients while providing ideal soil structure, potting soil is the best choice for seed starting, transplanting, and up-potting. The loose potting soil is gentle to traumatized root hairs and eases the transition. Potting soil is also the best choice for vertical gardening, tower gardening, and raised beds.