If you are into container gardening, you know that potting soil can be expensive, especially if you have a large number of pots to plant. Learn to make potting mix from materials commonly found at the garden center and save money in the process.
Since my personal preference is never to use anything that is not organic and to not use potting soil that already has fertilizer in it, I create a specialized mix. I want my container garden to be as natural as possible and I want to have ultimate control of all the amendments.
Ingredients for Potting Mix
You can make your own enhanced potting mix by purchasing a bag of garden soil and mixing in a bag of garden compost. These are the foundation of the potting mix and the way to go if you need a large quantity of soil while still trying to save money. Consider adding a few of these ingredients to give it water holding power and loosen it up for container gardening.
Sphagnum peat moss has a coarse texture and contributes to proper aeration, yet provides the water holding capacity to prevent soil from drying too quickly. Adding too much sphagnum peat, however, can restrict soil drainage by keeping too much water. It can be difficult to wet and should be moistened before mixing in with the other ingredients.
Perlite is expanded volcanic rock. Consider adding it to both peat-based and soil-based potting media in place of sand. Like sand, perlite provides excellent drainage, but is lighter in weight and holds more air. Although more expensive than sand, the advantages may outweigh the additional cost.
Disadvantages of perlite include:
- a tendency to float to the top of the medium when watered;
- an inability to hold or retain water; and
- a need to be moistened before it is mixed with other ingredients to reduce dust, which is harmful if inhaled.
Coarse, sharp, or builder sand, often used in construction, is a primary ingredient in potting media. Like peat moss, sand improves drainage and aeration but does not improve water-holding capacity. Too much sand will make containers too heavy to move. Sand should not be mixed with a clay-based soil, or you’ll make concrete in your pot.
Vermiculite is often used instead of perlite. Vermiculite is clay belonging to the mica family and is found naturally in laminated flakes. It expands when folds of vermiculite can hold water, nutrients, and air, unlike perlite. Only horticultural grades, sold at garden centers, are recommended.
Making Soil-based Potting Mix
The following is a basic recipe for soil-based potting media from Penn State University Extension. In this recipe garden loam soil, coarse construction sand, and sphagnum peat moss are combined in equal parts by volume:
- Start with one gallon of sterilized loam soil, commonly called garden soil and sold at garden centers, and pour it into a clean, empty 18-gallon plastic tub. Sterilized loam soil is worth the cost to avoid disease, insect, and weed problems that may exist in the unsterilized soil.
- Add one gallon of moist, coarse sphagnum peat moss, followed by one gallon of coarse sand, perlite, or vermiculite.
- Add one gallon of garden compost or composted manure.
- Adjust the texture of the medium to create a loose, well-drained mixture. Sand feels gritty, and clay feels sticky. If the potting soil feels too sandy, add more peat moss. If the potting soil feels too sticky, extra sand and peat moss should be added. Adjust the texture by adding small portions of sand and/or peat moss until you are satisfied with the feel of it.
Keep any extra soil mix in the plastic tote and cover it with a lid so you will have it available when needed. Then you can scoop out what you need and not have to worry about mixing a new batch very often.
Read more about creating organic potting mixes in this article from the University of Vermont Extension office. Also, the Maine Organic Farmers and Gardeners Association has recipes for four different soil-less mixes in their publication Soil-less Mixes for Vegetable Production.
The advantage of commercially prepared mixes is that they are of consistent quality and you can expect to get the same result form every bag. The disadvantage of homemade mixes is that they often are not dependably consistent. Create a recipe that you like, it will come in handy each year as you are preparing to make a new mix.
Change Potting Mix Yearly
Be prepared to change (or refresh) the soil in container gardens every year. You cannot continue to use that old soil and get good growing results.
At the beginning of the next growing season remove at least half of the soil in the pot and put it in the compost pile. Then add new soil from the tote as you’re planting new vegetables and herbs. This gives them a fresh medium to start the season and will give you the biggest harvest.