Homemade Potting Mix
Gardeners use various potting mixtures for seedlings, transplants, and container plants. These mixtures combine a variety of ingredients to provide a good growing environment for plant roots.
Commercial pre-packaged potting soils are widely available at nursery and garden supply stores, but you can also make your own potting mix at home. Making your own mix allows you to control the types and proportions of ingredients to customize your potting mix to meet your needs.
A good potting mix should:
- Be dense enough to support the plant.
- Hold nutrients well.
- Allow for air and water flow while retaining moisture.
- Be free of pathogens and weed seed.
Potting mediums must meet plant root requirements for air, water, nutrients, and support, which vary for different plants and growth stages. Despite the differences in types of potting mixes, they share common ingredients, just in different amounts.
Soilless mixtures are common due to density and disease concerns. Some organic blends still use soil. Clean topsoil or garden soil can be used and should be sterilized to kill disease organisms and weeds. Spread soil in a tray and bake at 200º F for twenty minutes, stirring every five minutes.
Sand adds air space to a potting mix. Builder’s sand, or coarse sand, is best. Avoid plaster and fine sands; they create a dense mix. Because it is heavier than other ingredients, sand is a good choice for top-heavy plants that might tip over.
Compost is cheaper than traditional ingredients, holds water well, provides nutrients, and can be produced at home. The nutrient quality of compost will depend on the quality of the materials that were composted.
Bark creates a light mix with air space but low water holding capability. It degrades slowly and is a good component for mixes for potted ornamentals. It may be partially substituted for peat moss.
Sphagnum Moss & Peat
Peat moss is the most common ingredient for soilless mixes because it is widely available and inexpensive. Peat moss decomposes slowly and holds large amounts of water; however, it has a high acidity. Lime is usually added to mixes to balance the pH. Ground-up newspaper can be used as a peat moss substitute.
Coir, a by-product of the coconut fiber industry, looks like sphagnum moss, but is granular, doesn’t contain twigs or sticks, and is more expensive. Coir typically is packaged as a compressed brick that will expand when wetted. It is important to note that coir may require less potassium and increased nitrogen supplementation. There is also the chance of salt damage since salt water is used in its processing.
Perlite is a sterile and pH-neutral lightweight volcanic rock. It increases air space, improves water drainage, and is a good lightweight replacement for sand.
Vermiculite is another lightweight addition to potting mixes. Handle it gently; if it’s handled roughly, it compacts and loses its air-holding ability. Medium grade is suitable for seedlings, while coarse grade is better for a soil mix for older plants.
When making your own potting mix, working from a recipe is a good idea to start. Once you begin experimenting with your own blends, try small test batches to evaluate the mix’s quality. See the recipes below to get started making your own potting mixes.
- 2 parts peat; 1 part perlite; 1 part coarse sand
- 1 part peat; 1 part pine bark; 1 part coarse sand
- 2 parts soil; 1 part peat moss; 1 part perlite; 1 part coarse sand
- 1 part peat; 1 part bark; 1 part coarse sand
- 2 parts compost; 2 parts peat moss; 1 part vermiculite (pre-wet)
This mix is heavier than peat-based mixes, but it has good drainage. Vermiculite or perlite can be used for sand.
- 1/3 compost; 1/3 topsoil; 1/3 sand
This mixture is for use as soil blocks for seedling/transplant growing. Mix all ingredients together thoroughly. Ingredients can be measured with a standard 10-quart bucket.
- 30 quarts brown peat
- 20 quarts sand or perlite
- 20 quarts compost
- 10 quarts soil
- 3 cups base fertilizer (equal parts blood meal, colloidal phosphate, greensand)
- ½ cup lime
Adapted and excerpted from:
George Kuepper, "Potting Mixes for Certified Organic Production," National Sustainable Agriculture Information Service (rev. 10/2010).