I’m a huge fan of container gardening, and I know I’m not alone. Urban and small-space gardening is on the rise, houseplants are strutting their stuff all over Instagram, and few people have the time and energy to dedicate to a large in-ground garden these days. But with hundreds of seedlings to start and over 50 large pots to fill each season, my container gardening habit used to come with a hefty price tag. When I started making my own DIY potting soil, however, I cut my container gardening budget by two-thirds! Here’s how I make homemade potting mix for all of my containers, houseplants, and seed-starting needs.
What is potting soil?
Before I introduce my favorite DIY potting soil recipes, let’s talk about what potting soil actually is. The most important thing to understand about potting soil is that it doesn’t actually contain real soil. Potting soil, also called potting mix, is a soilless blend of ingredients used to grow plants. Whether you’re starting seeds, rooting cuttings, potting up houseplants, or growing patio containers and hanging baskets, potting soil is the ideal growing medium for containerized plants. All good-quality potting mixes, including homemade potting soils, have a few things in common.
- They’re better draining than the average garden soil.
- Potting soil is more lightweight than garden soil.
- It’s easy to handle and consistent.
Like commercial potting soils, you can make many different DIY potting soil blends, each with a different texture, nutritional content, density, and water-holding capacity, all matched to the needs of your plants. Carefully select the ingredients you use and combine them in the correct ratios to tailor each DIY potting soil you make for the specific needs of each plant you’re 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 gravely 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’s suitable for growing lots of different kinds of plants.
There are dozens of specialized potting soil mixes you can make.
Potting soil ingredients
Most commercial and homemade potting soils consist of a blend of the following ingredients:
Sphagnum peat moss:
The primary ingredient in most potting soils is sphagnum peat moss. A very stable material, peat takes a long time to breakdown and is widely available and inexpensive. It bulks up potting mixes without adding a lot of weight, and once wet, it holds water fairly well.
Sphagnum peat moss is well-draining and well-aerated, but it’s very low in available nutrients and it has an acidic pH, typically ranging between 3.5 and 4.5. Limestone is added to peat-based potting mixes to help balance the pH. I use bales of brand peat moss for my homemade potting soil, blended with crushed limestone at a rate of 1/4 cup lime for every 6 gallons of peat moss.
A by-product of the coconut industry, coir looks and acts a lot like sphagnum peat moss in both commercial and DIY potting soil blends. It has more nutrients than peat moss and lasts even longer, but it’s more expensive to purchase. Coir fiber’s pH is close to neutral.
Often sold in compressed bricks, coir fiber is considered by many to be more sustainable than sphagnum peat moss. BotaniCare is one available brand of compressed coir fiber.
Perlite is a mined, volcanic rock. When it’s heated, it expands, making perlite particles look like small, white balls of Styrofoam. Perlite is a lightweight, sterile addition to bagged and homemade potting mixes.
It holds three to four times its weight in water, increases pore space, and improves drainage. With a neutral pH, perlite is easy to find at nurseries and garden centers. One popular brand of perlite is Espoma perlite.
Vermiculite is a mined mineral that is conditioned by heating until it expands into light particles. It’s used to increase the porosity of commercial and DIY potting soil mixes. In potting soil, vermiculite also adds calcium and magnesium, and increases the mix’s water-holding capacity.
Though asbestos contamination was once a concern with vermiculite, mines are now regulated and regularly tested. Organic bagged vermiculite is my favorite source.
Coarse sand improves drainage and adds weight to potting mixes. Mixes formulated for cacti and other succulents tend to have a higher percentage of coarse sand in their composition to ensure ample drainage.
Add pulverized calcitic limestone or dolomitic limestone to peat-based potting soils to neutralize their pH. Use about 1/4 cup for every 6 gallons of peat moss. These minerals are mined from natural deposits and are readily available and inexpensive. Use good brand of lime for use in DIY potting soil.
Add fertilizers to peat-based potting soils because these mixes don’t naturally contain enough nutrients to support optimum plant growth. A good DIY potting soil recipe includes a natural fertilizer, derived from a combination of mined minerals, animal by-products, plant materials, or manures, rather than a fertilizer that’s comprised of synthetic chemicals.
I use a combination of several natural fertilizer sources for my homemade potting mixes. Sometimes I add a commercially-made, complete organic granular fertilizer, such as Dr. Earth or Plant-Tone, and other times I blend my own fertilizer from cottonseed meal, bone meal, and other ingredients (my favorite fertilizer recipe is provided below).
Composted wood chips:
Composted wood chips lighten up potting mixes by increasing the pore sizes, and allowing air and water to travel freely in the mix. They’re slow to breakdown but may rob nitrogen from the soil as they do, so the addition of a small amount of blood meal or alfalfa meal is necessary when using composted wood chips as an ingredient in DIY potting soil recipes. Use composted wood chips in potting mixes designed for potted perennials and shrubs. To make your own, get a load of wood chips from an arborist and let them compost for a year, turning the pile every few weeks.
Containing billions of beneficial microbes, and with superior water-holding capacity and nutrient content, compost is an excellent addition to DIY potting soil. Because it plays such a huge role in promoting healthy plant growth, I use it in all of my general homemade potting soil recipes. But, I don’t include it in recipes for seed-starting as it’s too heavy for young seedlings. I use leaf compost from a local landscape supply yard, but bagged compost from Dr. Earth Compost or Coast of Maine are other favorites.
Good quality, DIY potting soil should be light and fluffy, with a well-blended mixture of ingredients. When it’s dried out, it does not shrink significantly or pull away from the sides of the container.