If you’ve ever tried to grow container plants in regular garden soil, you’ve probably noticed that they don’t do too well. This is because soil compacts in containers, leading to drainage issues, stunted roots, and unhealthy, unhappy plants. Let’s take a look at what makes ideal potting soil for container gardens, and how you can easily blend your own.
Basic Ingredients + General All-Purpose Recipe
When you’re mixing homemade potting soil, you’ll be using ratios of some basic building blocks. These are the ingredients that are best to work with.
- Coconut coir or peat moss: For nutrient suspension and water retention. Coir is more alkaline and sustainable, while peat moss is more acidic.
- Great for root system support and water drainage.
- Compost: This is your plant’s food source. Well-rotted compost (like manure) is incredibly nutrient-rich, and will keep your plants fed and thriving.
- Perlite: A type of volcanic glass that poof up like popcorn when heated. It’s perfect for aerating the soil and helping it drain.
- Vermiculite: This mineral also aids in aeration, but also absorbs and retains water to keep soil damp.
- Shredded Bark: If you’re cultivating thirsty plants, or you live in a hot, dry region, be generous with shredded bark. This stuff soaks up (and holds) water like crazy.
The basic recipe you’re going to follow is comprised of the following:
- 5 quarts compost
- 10 quarts peat moss
- 5 quarts perlite
- 4 quarts vermiculite
- 2 cups fine sand
- 2 cups slow-release fertilizer
- 1/3 cup lime
This will create enough potting soil for two 14-inch pots, or a couple of long windowsill troughs. Double or triple the recipe as needed for bigger pots, or to keep in sealed containers to use later.
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How Much Potting Soil Do I Need for My Container?
This is just a basic estimate, and it’s always a good idea to make a bit more soil than you think you’ll need. You can always use the extra for small indoor plants, or cuttings.
8-inch diameter: 3 quarts soil
10-inch diameter: 6 quarts soil
12-inch diameter: 8 quarts soil
14-inch diameter: 12 quarts soil
16-inch diameter: 20 quarts soil
20-inch diameter: 24 quarts soil
24-inch diameter: 28 quarts soil
12-inch diameter basket = 6 quarts soil
16-inch diameter basket = 10 quarts soil
24 x 6-inch window box = 12 quarts soil
36 x 6-inch window box = 20 quarts soil
Loose, Light Soil
When the soil in your containers is loose and light, your plant has a chance to stretch out a little bit. Roots can spread, and can take full advantage of the air, water, and fertilizer that’s moving freely around in there. The aeration also allows water to drain out freely so your plants don’t drown.
For a quick-draining mix, you’ll need to add material that lets water flow through easily. Perlite is ideal, as is coarse sand. Or a mix of the two.
If you’re cultivating species that need to keep a bit more moisture in the soil—or if you’re growing in terracotta pots that suck water out—add in peat or vermiculite. These retain water to keep your plant’s toes moist and happy.
Ingredients You Can Control
The potting soil you buy may be labeled organic, but that doesn’t mean that you know exactly what’s gone into it. For example, some soil wetters use plastic polymers (not great), as well as potentially harmful chemical fertilizers.
Most health agencies don’t test garden soils very stringently, so manufacturers have a lot of wiggle room. The average bag of potting soil doesn’t even have an ingredients list on it. Best to err on the side of caution and blend your own.
Best of all, you can adjust ingredients to suit the type of plant you’re growing. Some heavy feeders require richer, more compost-rich soil, while others prefer that which is sandier. Different species may have different pH needs as well, so you can add various amendments for ideal, happy plants.
Related post: Compost Tea—How to Brew It and Use It in Your Garden
Additives for Different Plant Needs
The aforementioned rich soil is ideal for those in the Cucurbitaceae family (pumpkins, squashes, cucumber), and it needs to be only slightly acidic. If you need to bulk up nutrients for these babies, mix in well-rotted manure or worm castings.
Nightshade vegetables (tomatoes, eggplants, peppers) like slightly more acidic soil with moderate fertility. Try a 1:1:3 ratio of leaf mold, coconut coir, and compost for their beds.
*Note: You’ll likely need to add fertiliser to your containers during both the flowering and fruiting stages. For this, it’s good to do a bit of research to determine which N-P-K (Nitrogen, Phosphorous, Potassium) ratios the species you’re growing will need to thrive best.
Protect Your Health While You’re Working
Now, we all know that gardening is spectacular and provides a ton of positive health benefits. That said, there are types of bacteria that can live in compost and certain potting soils that can be detrimental to us, especially if we have weak pulmonary systems.
Legionnaire’s Disease, for example, is a severe form of pneumonia that can be caused by inhaling said bacteria. As a result, it’s a good idea to wear a face mask and goggles so you don’t inhale anything nasty, nor get it into your eyes.
Use gloves while you’re working, and make sure to only mix soil on fairly still days. Strong winds will just undermine your efforts and coat you in particles. If you’re working with dusty ingredients, use a spray water bottle to keep the dust under control.
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