Shopping for garden soil can be confusing. There’s a lot more to soil than just dirt. Healthy soil is a combination of minerals, water, air, living and decayed organisms. Garden soil, or topsoil, is a natural soil found in the ground. It usually must be amended in order to provide plants the structure and nutrients needed for healthy, vigorous growth. Potting mixes are artificial media for growing plants in pots or containers. Don’t be tempted to use topsoil or soil from the ground in containers. When topsoil is used in containers, it can harden to the point where the roots won’t be able to absorb enough moisture or oxygen. Soil from the ground can also harbor diseases, insects and weeds.
Here’s where it gets complicated. The terms potting mix and potting soil are used interchangeably. Despite the name, there’s no earth in the mix at all. Potting mixes are artificial soils blended to promote drainage, aeration and moisture retention. Some contain nutrients to get your plants off to a good start. Ideal potting mixes are lightweight and fluffy.
There are many commercial potting mixes available. If you want to give square foot gardening a try, or you have lots of containers to fill, it can be expensive. Blending your own is an easy way to save a lot of money. Here’s the recipe that Rachel and I have been using for years. Mix equal parts by volume (not weight): one-third sphagnum peat moss, one-third composted cow manure and one-third equal blend of perlite and vermiculite.
The white specks in the potting mix that look like styrofoam are actually perlite and vermiculite. These are two naturally occurring minerals. Perlite improves water holding capacity while vermiculite improves drainage. If you can’t find both, either one will do. Peat moss is lightweight, resists compaction and slightly increases acidity (great for tomatoes). Compost is the end product of decaying plant matter and contributes to the soil structure. Cow manure provides the nutrients that your plants need to grow. This is just a basic recipe. Feel free to add what works best for you.
Are potting mixes reusable? Absolutely. Sift through each container to remove as much of the old plant material as possible. You’ll need to replenish the nutrients, so add equal parts new potting mix and composted manure each growing season. If your small pots have held diseased plants, just throw the soil onto your compost pile. You can cover large containers with black plastic bags and let the sun bake them for three or four weeks. This natural pasteurization will kill any pathogens. We’ve been reusing our potting soils for more than 10 years with no problems. Plants grown in containers will need to be fertilized on a regular basis because frequent watering leaches out vital nutrients.
Over time, the potting soil in your containers will settle. This is just a natural part of decomposition. Each spring, we turn our raised beds with a pitch fork before adding fresh soil. This keeps the mix crumbly and airy enough for the plant roots to penetrate easily. We just combine the mulch into the mix. This doesn’t work for indoor potted plants. Simply adding more soil won’t do. You have to remove the plant from the pot, gently teasing the roots free. Repot the plant using fresh mix and a bigger pot if necessary. Make sure to keep the plant level at two inches below the rim.
Filling large containers can be costly. Take your time and spread out the expense. We’ve been adding to ours for years.
Rachel and Ivan Minnis are avid gardeners. They live in Leavenworth. For more information, visit The Minnis Rose Garden on Facebook. Contact them at firstname.lastname@example.org