Quality potting soil is incredibly important for your container plants. There are many different pre-mixed options available, but you can often get the best (and cheapest) mix by making DIY potting soil yourself. As there are many different applications for potting soil, there also are many different recipes! Read on to find the best potting mix for you and your garden.
(Don’t forget to grab your free printable copy of the DIY potting soil mix recipes at the bottom of this post).
Why Use Potting Soil?
Garden soil is wonderful for outdoor plants in the ground where it is part of the whole eco-system, but there are some drawbacks when used in containers. Potting soil is used in container plants rather than garden soil for several important reasons.
Garden soil can have too much clay, too much sand, not enough organics, or other reasons that make it unsuitable for certain plants. Existing soil can also be contaminated (particularly in urban or industrial areas). You also have to bend all the way down to the ground to tend plants in the ground. Walking on the soil compacts it, squishing air voids and making it harder for the plants to grow.
Many gardeners who start gardening in the ground eventually decide to build raised bed gardens and fill them with potting soil. That way, they can select exactly the soil they want! The growing mix added to the beds can be light and airy, with good drainage and the ability to warm up quickly in the spring. That’s much better than a cold garden bed of heavy clay.
Once you learn how to make your own DIY potting soil, you’ll love being able to whip up a batch of the perfect mix whenever you get new plants. It will definitely make you a better gardener!
Let’s Look at Some Common DIY Potting Soil Mix Ingredients
Most potting mixes are made from a combination of the following ingredients:
- Mineral-Rich Soil
- Worm Castings
- Peat Moss
- Coconut Coir
There are different reasons for adding each of these ingredients to a DIY potting soil mix. Each ingredient has different features, so they’re blended to create a mix with certain properties unique to the plant that will grow in it. Here is a description of each soil mix ingredient:
Soil: Mineral-Rich Mix of Sand, Silt, and Clay
Soil is a general term for a mixture of clay, silt, and sand, with pore spaces full of air or water. It may also contain organic material. A particular soil may have more of one mineral component than another. For instance, a soil that is mostly sand might be referred to as a sandy soil. Sand helps your soil drain, while silt and clay retain water and hold required nutrients for your plants.
Using natural soil from the ground in your potting soil mixes has the benefit of being free if you happen to have a backyard. If you’re lucky enough to have a “loamy soil” in your backyard, enjoy a moment of gratitude. Loam is a healthy mix of sand, silt, and clay in which none of the particle types takes over. There is enough sand for the soil to drain well, but enough silt and sand to retain nutrients and enough water for the plants. Uncompacted loam will also be porous, having lots of air space for the roots of the plants.
A caution about garden soil is that it may be contaminated. If the soil has been beside a roadway, it may be contaminated with lead, petroleum, road salt, and other environmental contaminates. If the soil has been in an urban area, it may have be contaminated by cats and the diseases they carry. It can also be contaminated if it was affected by nearby industry. Lastly, the soil may have been brought in by a builder, and could have be contaminated in it’s original location. Many gardening experts recommend having your garden soil tested before growing food crops for human consumption. Wearing gloves is also a must when working in garden soil.
Another caution about garden soil is that it is not “sterile”. It is full of micro-organisms, fungi, bugs, and other lovely creatures which make their home in the soil. This is what makes it magic! But, it is definitely not sterile. For this reason, I skip the garden soil in seed starting mixes. The garden soil may be harbouring some nasty germ/bug/fungus which could kill a tiny seedling. I don’t chance it for my seedlings.
Topsoil: Natural Soil Rich with Organics
Topsoil is the upper layer of existing soil. It consists of minerals, organic matter, water, and air. The soil at the surface has the highest concentration of organic matter and soil-borne life. Most life in soil happens in the topsoil.
Because topsoil is rich in the organic material that supports life, it can be a gardener’s dream. If you’re lucky enough to have nice topsoil in your back yard, consider yourself lucky! If you buy topsoil in bags, be sure to check out the source of the soil and also check to ensure that no chemical fertilizers have been added. If you’re buying bulk topsoil, you’ll also want to ask for a testing certificate to show that the soil hasn’t been contaminated with heavy metals or any other nasty things (as with regular mineral-rich soil).
Compost: Homemade Organic Garden Gold
Compost is the magic ingredient in most soil outdoor mixes. Compost is a wholesome and sustainable soil amendment full of nutrients created by decaying plant matter such as leaves, food scraps, and coffee grounds. The best kind of compost is homemade organic compost, but there are also bulk and bagged options available.
Making Your Own Homemade Compost
Making your own compost can be easy with a bit of prep work. You’ll either need to buy or build a composter. My dad built mine with some extra wood plants and some cinder blocks. Once your composter up and running, you simply keep adding volume and collecting finished compost.
Composting can help make your household more sustainable. Making your own compost is a wonderful way to start using your kitchen and yard waste rather than having it trucked to the landfill. Check out these instructions for composting your leaves and other plant-based waste.
To make awesome compost, focus on lots of shredded leaves. Shredded leaves are the gold standard compost ingredient. Coffee grounds will help add nitrogen to all that leafy carbon. I pick up a bag of free coffee grounds from the coffee shop whenever I stop by for a chai tea latte. Gotta love it!
As with outdoor garden soil, homemade compost is not “sterile”. Although I LOVE homemade compost, I don’t use it in seed starting mixes due to the possibility of pathogens or harmful fungus sneaking in and harming the baby seedlings while they are most vulnerable.
Finding and Purchasing Compost
If you don’t yet make your own compost, or if you don’t have enough, you can find or buy some compost to add to your DIY potting soil. A great place to find free compost is your local municipality. If they collect yard waste in the spring and fall, there is a chance that they are shredding and composting that material.
Many municipalities will give away bulk compost in the springtime, free of charge. You’ll need a truck or some large buckets to bring the compost home with you. You’ll also want to check the test results for the compost to get an idea of the nutrient concentrations and to ensure it does not contain toxins or harmful chemicals (municipalities test their compost prior to distributing it, and can provide the results if you ask for them).
If free, high-quality compost isn’t available, a great new source of compost are the companies that now provide composting services to the food service industry. These new facilities hot-compost food waste from restaurants into compost, which is often available for purchase by the public. They can also provide test results to you so you know what you’re getting!
If you can’t find any compost available locally, you can always pick up a bag or two at the local garden centre or online.
Buying Compost from Local Farms
One last place that some people get compost from is local farms. If I’m buying compost from a local farm, I like to ensure it’s an organic farm so that I know no chemicals have snuck into the process.
When you buy compost from a farm, it’s generally composted animal manure. It will include some of the animal’s bedding materials (straw, et cetera) as well as the manure. Look for a farm that feeds their animals a wide variety of organic food. You also must check to ensure the manure has been hot-composted to thoroughly destroy any seeds that might be in the manure.
Aged composted manure is best, as some types of composted manure can “burn” your plants due to the chemical makeup while they are fresh. If you do plan to use composted manure, do some research on the different types of animals and the features of their manure. All composted manure is not created equal!
Worm castings, or Vermicompost, are basically composted worm poop. Worms, wonderful garden allies, feed on your kitchen scraps and newspaper in a special bin to create a nutrient-rich product for your garden. Worm castings are garden gold, and are a wonderful addition to garden soil. Indoor vermicompost systems are available for those living in small spaces or without yards large enough for traditional compost heaps.
Worm castings are a great option for feeding your seedlings before they go outside. Save the homemade compost for outdoor applications, like a nice top dressing on the garden or around your baby trees. You can make your own worm castings with a home worm bin or purchase them locally or online (they don’t smell!).
Perlite: Adding Air to Your Roots
Perlite is a mined mineral which is added to soil mixes to help the soil hold air. The mineral is “popped” using heat like popcorn to create a light, air-filled medium. Perlite is an organic amendment, as it is chemically inert. It will help to hold air in the soil, keeping the plants from suffocating. Some of the Perlite will float to the top of your plant container over time as it is much less dense than the other materials in the soil matrix. It can be purchased at a local garden centre or online.
Some gardener’s prefer to use Vermiculite rather than Perlite. Vermiculite is generally darker in colour than Perlite, and blends well with the soil colour. It also does not float to the top quite as much. There have been some reports of Vermiculite being potentially contaminated with asbestos. Asbestos was once discovered in a Vermiculite mine, causing reports of contaminated Vermiculite. If you do choose to use Vermiculite, make sure to pick a brand which certifies it’s product as being free from asbestos.
Always wear a dust mask when mixing in Perlite or Vermiculite to soil. There is no reason to put your lungs in danger by inhaling the dust from these products, even if it is not contaminated with asbestos. Dust masks are inexpensive, and also make you look like you know what you’re doing!
Peat Moss: Organic Bulk Material
Peat moss is a mined organic material composed of partially decayed plant matter. Although it is comprised only of organic material, it is not truly a renewable material as it takes thousands of years for wetlands to develop into peat reservoirs. If you do choose to use peat moss in your DIY potting soil, do your research to ensure it is coming from a reputable provider in your area. Look for a brand which is practicing ecological conservation to offset the effects of mining out a valuable carbon sink. If you live closer to the tropics than to peat bogs, consider using coconut coir rather than peat moss as a more sustainable local alternative.
Peat moss is an acidic material. Most plants prefer soil with a neutral pH, although there are some which prefer acidic soil (such as blueberries). You may need to offset the acidic pH with limestone if peat moss is used for alkaline-loving plants. Most pre-mixed potting soils and growing mediums that contain peat will also contain some limestone as a pH adjuster. You may even be able to find bulk peat moss which has been pH adjusted using limestone.
Coconut Coir: The New Organic Bulk Material
Coconut coir is a growing medium made of shredded coconut skins, used to add bulk to a DIY potting soil mix. It has the benefit of not being a mined product, and instead provides a use for something that may have been a waste product. If you’re looking for a more sustainable alternative to peat moss, or would like a more pH-neutral product, look into buying coconut coir instead.
The downside of coconut coir is that it needs to be transported to northern areas, where coconuts don’t grow. If you live far away from the production of coconut coir, you’ll have to weigh the sustainability of transporting the coir to your area versus other alternative. Check out what’s available in your area and decide what’s best for you. Some people choose to mix peat and coir to get the benefits of both and balance out the drawbacks.
DIY Potting Soil Mix Recipes
Onto the best part!…the potting soil mixes. Potting soil should be light, but also be firm enough so that the plant can develop a strong root foundation. It should be porous and airy, with lots of room for water to drain through.
A potting soil mix that includes non-sterile ingredients should be rich in beneficial components, such as fungus that can develop a beneficial relationship with the plants in the garden. It should also be free of weeds, weed seeds, harmful fungi, and pathogens.
You can grab a free printable cheat sheet for the soil mix recipes using this form:
Printable DIY Potting Soil Recipes
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DIY Potting Soil Mix #1: Sterile Seed Starting Mix
Seedling potting soil mixes should be light, firm, and able to retain moisture to help the baby seedlings thrive. Sterile seed-starting mixes also shouldn’t contain outdoor soil or compost, as it may include fungi, pathogens, or weeds that could harm the seedlings.
The mix below is sterile and weed-free. Each material can be purchased from your local independent garden centre. The drawback to seed-starting mix is that these materials have to be purchased, rather than sourced at home. Therefore, make sure you do need sterile weed-free seedling mix before shelling out the extra money for these ingredients.
Ingredients: Sterile Seed-Starting Mix
- 3 Parts Coconut Coir (prepared, not in raw block form)
- 3 Parts Peat Moss (pH-balanced with limestone if possible*)
- 3 Parts Perlite
- 1 Part Worm Castings
- Filtered Water
These ingredients are to be mixed by volume rather than by weight.
*If you can’t find pH-balanced peat moss, substitute the peat moss and the perlite in the mix above with plain Pro-Mix HP. It comes in large bales like peat moss. It is pretty much just peat moss and perlite, plus some limestone for pH balancing. The real benefit, however, is that the whole mix is inoculated with Mycorrhizae. Mycorrhizal fungi acts as a buddy to seedlings, helping them absorb water and nutrients as well as strengthening their root systems.
Steps: Sterile Seed-Starting Mix
- Estimate how much soil you’ll need to fill up your seed-starting containers.
- Find a mixing bowl or bucket that will accommodate the amount of soil you’d like to mix up.
- Find a small measuring container to use when measuring out the parts. The mix above is a 10-part mix. This means that you’ll need to find something small enough so that 10 of the smaller measuring units will fit comfortably in the mixing container you’ve selected. I usually use a cup measure if I’m just mixing up a bowl of soil for a single seedling tray, or I use an empty yogurt container if I’m mixing up a whole bucket of soil.
- Find a trowel to mix up the soil with.
- Ensure the bowl/bucket, measuring container, and trowel are clean and sterilized.
- Mix all ingredients except for the water together with the trowel.
- Slowly add filtered water, mixing with the trowel. Stop when the soil becomes moist. Don’t add enough water that the soil becomes wet and muddy.
- Use the trowel to place the seedling mix into your seed-starting containers or trays.
- Compress the soil gently before planting your seeds.
- Plant your seeds in the seedling mix before it dries out.
DIY Potting Soil Mix #2: Outdoor Soil-Based Container Mix
This mix is a low-cost, homemade option for filling up large containers. If you have easy access to clean topsoil and some homemade compost, you’ll only have to buy the perlite. I like to mix up the soil, wait for any weed seeds that have snuck in to germinate, and then pull any weeds that come up before planting out the mix.
Before you create this mix for your plants, consider what types of plants you’ll be growing in it. Do some research about what kind of growing environment the plant enjoys out in nature. For a plant that grows well in the desert or dry areas, consider using a sandy topsoil. For plants that prefer acidic growing conditions, try to source an acidic topsoil. Paying a little bit of attention to a plant’s natural environment will help you make a wonderful custom mix for your plants.
Ingredients: Soil-Based Container Mix
- 1 Part Topsoil
- 1 Part Compost (Homemade is best!)
- 1 Part Perlite
- Water (Rainwater is best, but not required)
These ingredients are to be mixed by volume rather than by weight.
Steps: Soil-Based Container Mix
- Estimate how much soil you’ll need to fill up your growing containers.
- Find a mixing bucket or wheelbarrow that will accommodate the amount of soil you’d like to mix up.
- If you want to be super-specific with the amounts, find a measuring container that is small enough so that 3 full measuring containers will fit comfortably in your mixing vessel.
- Find a trowel or shovel to mix up the soil with.
- Mix all ingredients except for the water together.
- Slowly add water, mixing as added. Stop when the soil becomes moist. Don’t add enough water that the soil becomes wet and muddy.
- Shovel the mix into your growing containers.
- Gently compress the soil into the containers.
- Moisten soil before and after planting.
Try out these DIY potting soil mixes and see what works best for you in your situation. Share what you use for your DIY potting soil mixes, or your questions, in the comments section below!
Grab your free printable copy of the DIY potting soil mixes using this form:
Printable DIY Potting Soil Recipes
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