Sphagnum peat moss – this is the primary ingredient in most potting soils. It takes peat a long time to breakdown is widely available and inexpensive. It will bulk up potting mixes without adding weight and once wet, holds water pretty well. Sphagnum peat moss is well-draining and well-aerated but it is also very low in available nutrients and has an acidic pH ranging between 3.5 to 4.5. Adding limestone to peat-based potting mixes helps balance the pH level. Plants such as lettuce, Russian sage, and marigolds prefer sweet soil with a pH of 7.5, while other acid lovers, like ferns, asters, and strawberries prefer a pH of 5.5 to 6.0. Here is a list of more plants’ pH preferences.
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Making Your Own Potting Soil
March 30, 2023
Potting soil is a soil-less blend of ingredients used to grow plants. Potting mixes are filled with organic matter that provide essential nutrients to plants. Conventional potting soil can often be full of chemicals that can harm plants.
All good quality potting mixes have a few things in common:
- Better draining than the average garden soil
- More lightweight than garden soil
- Easy to handle and consistent
Like commercial potting soils, you can make different potting soil blends, each with a different texture, nutritional content, density, and water retention to match all the needs of your plants. You will need to select the ingredients and combine them in the correct ratios to tailor each potting soil mix for the specific plant you are growing.
- Lighter, finer-textured mixes are best for use when starting seeds and rooting cuttings.
- Mixes containing a high percentage of coarse sand or pine bark are best for potted trees and shrubs.
- DIY potting soil with a sandy or gravelly texture is ideal for cactus and succulent growing.
- When growing a mixture of annuals, perennials, vegetables, and tropicals, the best fit is a general, all-purpose potting mix, one that is suitable for growing all kinds of plants.
Interesting fact: despite its name, little or no soil is usually in potting soil
Potting Soil Ingredients
Coir fiber – this is a by-product of the coconut industry. It looks and acts like sphagnum peat moss in both commercial and DIY potting soil blends. It is often sold in compressed bricks; coir fiber is considered by many to be more sustainable than sphagnum peat moss.
Perlite – perlite is mined volcanic rock. When heated, it expands, making perlite particles look like small white balls of Styrofoam. It is a lightweight, sterile addition to bagged and DIY potting mixes. It can hold three to four times its weight in water, increases pore space, and improves drainage. It has a neutral pH and can be found at garden centers.
Vermiculite – a mined mineral that is conditioned by heating until it expands into light particles. It is used to increase the porosity of commercial and DIY potting soil mixes, increase the content of calcium and magnesium, as well as increase the water retention of the mix.
Sand – coarse sand improves drainage and adds weight to potting mixes. Fertilizers act more quickly in the soil if the amount of sand is higher. It helps in proper airflow in the soil. It will help ensure your plants get enough oxygen.
Limestone – you can add pulverized calcitic or dolomitic limestone to peat-based potting soils to neutralize the pH level. Use about ¼ cup for every 6 gallons of peat moss.
Fertilizers – you will need to add fertilizer to peat-based potting soils because the mixes do not naturally contain enough nutrients to support optimum plant growth. A good potting soil recipe includes a natural fertilizer, derived from a combination of mined minerals, animal by-products, plant materials, or manures.
Composted wood chips – these lighten up potting soil mixes by increasing the pore sizes, and allowing air and water to travel freely in the mix. They are slow to break down but could rob nitrogen from the soil as they do, so adding a small amount of blood or alfalfa meal is necessary when using composted wood chips. You can easily DIY this – get a load of wood chips from a local arborist (like 4 Seasons Arborscapes!) and let the chips compost for a year, turning every few weeks.
Compost – compost is an excellent addition to your DIY potting soil. It contains billions of beneficial microbes, has a superior water-holding capacity, and a decent nutrient content. It is huge in promoting healthy plant growth.
Rice Hulls – this is one of the most sustainable soil amendments available for improving drainage, water holding capacity, and aeration. Unlike perlite and other rock products, it does not require mining. Rice hulls are the husks that are removed from each grain of rice after harvest. The hulls are parboiled at a high enough heat to sterilize any grains of rice that make their way into the mix. They add nutrients to the soil as they break down. For potting soil, rice hulls should make up 10-50% of the mix.
How to make your potting soil
Mixing your own potting soil blend is easy, and you have complete control, you can cater to the needs of your plants and shrubs. You will also save money making your own.
When combining the list of ingredients above, be sure to mix everything thoroughly. Good quality DIY potting soil should be light and fluffy, with a well-blended mixture of ingredients.
When making DIY potting soil, use the batch as quickly as possible. But if storage is necessary, place the mix in sealed plastic bags in a cool, dry place.
Some potting soil recipes:
General potting soil recipe for flowers, tropicals, and vegetables:
6 gallons sphagnum peat moss or coir fiber
4.5 gallons perlite
6 gallons compost
1/4 cup lime (if using peat moss)
1 & 1/2 cups of the DIY container fertilizer blend found below or 1 & 1/2 cups of any granular complete organic fertilizer
DIY container fertilizer blend:
Mix together
2 cups rock phosphate
2 cups greensand
½ cup bone meal
¼ cup kelp meal
Potting soil recipe for potted trees and shrubs:
3 gallons compost
2.5 gallons coarse sand
3 gallons sphagnum peat moss or coir fiber
2.5 gallons composted pine bark
3 gallons perlite
2 TBSP of lime (if using peat moss)
1 cup granular, organic fertilizer (or 1 cup of the DIY container fertilizer blend found above)
1/4 cup organic cottonseed meal, if growing acid-loving trees and shrubs
Potting soil recipe for succulents and cactus:
3 gallons sphagnum peat moss or coir fiber
1 gallon perlite
1 gallon vermiculite
2 gallons coarse sand
2 TBSP lime (if using peat moss)
Potting soil recipe for seed starting:
2 gallons sphagnum peat moss or coir fiber
2 gallons vermiculite
1 gallon coarse sand
3 TBSP lime (if using peat moss)
Seed-starting mixes are lighter and finer in texture. Vermiculite is a better choice than perlite due to its smaller particle size.
Homemade potting soil for transplanting seedlings:
2 gallons sphagnum peat moss or coir fiber
2 gallons vermiculite
1 gallon finely screened compost
3 TBSP lime (if using peat moss)
2 TBSP granular, organic fertilizer (or 2 TBSP of the DIY container fertilizer blend found above)
Potting soil recipe for houseplants:
2 gallons sphagnum peat moss or coir fiber
1.5 gallons perlite
2 cups coarse sand
3 TBSP lime (if using peat moss)
2 TBSP granular, organic fertilizer (or 2 TBSP of the DIY container fertilizer blend found above)
Basic container potting soil mix:
10 quarts coconut coir
5 quarts perlite
5 quarts vermiculite
5 quarts composted cow manure
2 cups fine sand
2 cups pelleted time-release fertilizer
This makes enough to fill two 14-inch tubs or five 12-inch hanging baskets.
When repotting houseplants, use your own homemade mix for optimal results.
References:
DIY Potting Soil: 6 Homemade Potting Mix Recipes for the Garden (savvygardening.com)
How to Make Your Own Potting Mix | DIY Potting Mix | The Old Farmer's Almanac
Optimum Soil pH Levels for Plants | The Old Farmer's Almanac
making your own potting soil - Bing images
How to Use Soil Amendments-Rice Hulls - Organic Gardening (groworganic.com)
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