Potting Mix Versus Garden Soil - Picking the Perfect Soil for Your Garden
In this post: Potting mix is considered a soil substitute for newer gardeners. But, are there better options? Find out whether using potting mix is the best option when you’re starting your new garden. Learn the difference between potting mix and garden soil. Learn which is best for your gardening needs.
What is the difference between potting mix and garden soil? And how do you pick the perfect garden soil to grow a healthy garden?
A lot goes into developing soil and your soil can differ depending on the type of garden and what you are growing. For example, vegetables can thrive in organic raised-bed soil, which might not be the best soil option for growing plants in pots. And if you’re still in the garden building phase, you’ll want to read my blog post on creating your perfect garden or how to build a garden for beginners.
Read on for my recommendations for picking the perfect garden soil for you in these topics below:
What is potting mix?
Potting mix and potting soil are two terms that generally mean the same thing and are often used interchangeably. When you think of soil, usually you think of the earth outside and that makes mud when wet. Potting mix or soil is not soil at all in that way and is often referred to as soilless.
Commonly, potting mix was a combination of peat moss, perlite, and vermiculite. Now, you can buy bags of potting mix with a variety of ingredients, which can include those traditional ingredients, but also other less traditional ones, like worm castings or composted manure. Specialty potting mixes are available with combinations of contents for growing particular types of plants, for example orchids, or purposes, like seed starting.
Benefits of using potting soil
Using potting soil has many benefits, especially for container gardening and seed starting.
Soil weight - potting soil is lighter in weight than garden soil
Soil texture - texture and ingredients prevent soil compaction
Pathogen free when sold - no insects, disease, fungi, or bacteria that could infect seeds, germinating seeds, or plants.
Flexible - available premixed or ingredients can be purchased to make own mixes for various types of plants, like houseplants, or uses, like seed starting or growing seedlings.
Drawbacks of using potting soil
One main drawback of using potting soil can be the cost. The ingredients that go into the mix are costly on their own, so if the potting mixes are being custom made from the different materials, that cost can add up.
Using potting soil premixed in something like a raised bed would also be more expensive than purchasing bulk garden soil and adding amendments, like compost.
Another drawback of potting soil is that peat moss is often the main ingredient. I talk about some of the questions around using peat moss in the section below.
Potting soil ingredients and considerations
Peat Moss
Peat or peat moss is very commonly used in potting soil or potting mix, especially in North America. Here are some reasons why peat moss might be used in potting soil or your own potting mix:
Light-weight - less likely to compact, improves drainage
Absorbs and retains water
Considered soilless
Free of pathogens, like insects, fungi and bacteria
Slightly acidic pH
Peat moss use has been questioned for environmental reasons. Peatlands, where peat is harvested, are places where atmospheric carbon dioxide is stored and are habitats for plants, animals, and ecosystems. Peat harvest can lead to removal or damage to the habitats for the species that live in and use the peat bogs for life.
The government of the United Kingdom has banned the sales of peat moss to gardeners in the year of 2024. The ban is for sales to gardeners, which means the ban would not necessarily apply to others, like developers or other similar industries.
Perlite and Vermiculite
Perlite and vermiculite are two ingredients usually found in the potting mix bags that you buy. You can also buy either of them separately to create your own potting soil mix or for other uses.
*TIPS - If you are unsure of which one is which in the bag of mix, perlite looks like tiny white balls of styrofoam or popcorn and vermiculite looks like small bronze-coloured, flaky chunks. And If you have trouble remembering the difference between perlite and vermiculite, use this trick: puffy-popcorn-perlite and vermiculite-see-shiny-light.
Perlite and Vermiculite
Not soil - Both perlite and vermiculite are mineral in nature but are not considered soil.
Lightweight - They are both lightweight but added to potting mix for different purposes. The light weight of both helps add volume to mixes without adding too much weight, like other options might e.g., adding sand to a mix would help with drainage, but sand is heavier.
Nutrient value - Provides none.
Perlite - Volcanic rock that expands after crushing and baking and can expand four to twenty times in volume when heated.
Porous (i.e., full of tiny holes) so helps to create air spaces in soil, which allow the soil to drain well.
Holds some water and can be used with hydroponic setups.
Vermiculite - Shiny and flaky mined material that expands 8 - 30 times the original size when heated to a high temperature and lightens in weight while heating.
Soaks up more water than perlite and can help keep potting mix from drying out.
Can be used in a thin layer on the surface of potting mix when germinating seeds to keep the soil damp without promoting fungal growth.
If you are creating your own potting or soil mix, some recipes call for one or both of perlite and vermiculite with amounts and ratios depending on the volume needed and what will be grown in the mix. For example, if more drainage is needed, a higher ratio of perlite might be used.
Coconut Coir
Coconut coir is used as an alternative to peat moss, though there is some question whether coconut coir is a more sustainable option. The choice between peat moss and coconut coir appears to depend on where each is sourced and how they are processed.
Coconut coir is made from coconut husks and is used for the following reasons:
Sterilized (no pathogens) and lightweight
Ability to store, absorb, and hold water
Changes the soil texture
Resists bacterial and fungal growth
Often sold in compressed bricks to be rehydrated before use
Bark
Some specialty bagged potting mixes include bark, like those for orchids, or bags of bark can be purchased separately for creating your own mixes. Bark is usually coarse, which increases the air spaces and drainage of the soil mix. Bark types can depend on the location that the mix was manufactured. In the North American Pacific northwest Douglas fir bark is commonly used, while other areas of North America bark may include different pine species.
Key differences between potting mix and garden soil
Potting soil is a combination of materials pre-mixed and sold in bags or created by the end user. And you can think of garden soil as the earth in the ground. You can also purchase garden soil that is “manufactured” by mixing ingredients.
How It’s assembled and made
Potting mix - When manufactured by a soil company, perlite, vermiculite, peat moss, compost, and other ingredients are mixed together in huge volumes and bagged to sell. Homemade potting soil can be made by buying the materials separately and blending in different ratios, as needed for different purposes.
Garden soil - Purchased garden soil is assembled by places like soil marts or garden centers where they sell the soil in the bulk or in individual bags. The garden soil is often made using a mixture of topsoil, compost, sometimes peat moss, and other materials, like sand or composted manure.
Material composition of the soils
Material composition of the potting mix and garden soil depends on what you want to grow. You want to mimic the natural growing conditions of the plants when choosing which materials to use in soils, i.e. how do the plants grow in nature? For example, rosemary prefers to grow in soil that is free-draining, so use materials that let the soil drain easily, like horticultural sand and compost, or if growing rosemary in-ground, sand or gravel could be blended in with the garden soil.
Potting mix - Pre-mixed bags of potting soil are available for many different types of plants and uses, like seed-starting mixes, or those for outdoor or indoor container gardens. Material composition is described in more detail above.
Garden soil - Whether already in the ground or purchased and added for creating lawns, trees, shrubs, or top dressing (i.e. adding to the ground’s surface) garden soil is often a blend of the following materials.
Top soil - technically taken from the top layer of earth, not ideal for containers on its own. If you’d like more information on top soil, here’s an article: Top Soil Requirements in Vancouver: The Need, the Benefits, and the Next Steps
Mineral or soil ingredients - e.g. sand, loam, sandy loam, rocks
Organic matter - e.g. compost, composted manure, peat moss, seaweed, wood or bark mulch
Garden soil (purchased) may also have organic fertilizers, e.g. bone meal, fish meal, or synthetic fertilizers, e.g. nitrogen, phosphorus, potassium (i.e. N-P-K) added.
Weight and density
Potting mix is lighter than garden soil because of the ingredients (e.g. perlite), but also it needs to be lighter for the intended purposes: containers, seed starting and seedling, and houseplants.
Garden soil is typically heavier in texture and weight than potting mix because the materials that make up garden soil are more mineral (i.e. tiny pieces of rock) in nature and so heavier.
Nutrients in the soil
Soil nutrients are the very basic plant food needed to survive and thrive, also called plant nutrients. Oxygen, hydrogen, and carbon are the main nutrients that plants need and use, which plants get from carbon dioxide in the air, and water and oxygen through the roots. Plants find the rest of the nutrients in the soil.
Soil nutrients are in organic matter, soil minerals, nutrients stuck to soil particles, and in water attached to soil particles. The nutrients you often see on labels for soil mixes and fertilizers are nitrogen, phosphorus, potassium, calcium, sulphur, and magnesium, and sometimes others, like zinc and iron.
Potting mix - If nutrients are added to bags of potting mix, and they aren’t always, they could be from an organic source, like seaweed or compost. Synthetic fertilizers, like ammonium nitrate or potassium phosphate may also be added. It’s best to look at the bag and check the ingredients, if you’re interested in what nutrients are added to the soil.
Potting soil is usually used for growing plants in containers, which limits the plants to the nutrients available in that soil. Nutrients will have to be added to the soil for the plants to thrive.
Garden soil - Garden soil you buy is likely to include some nutrients from the topsoil sourced for creating the soil. Nutrients will also be in any compost added to the garden soil blend from the compost’s organic matter. Some companies add fertilizer to garden soil, organic and/or synthetic. Again, it’s always best to read the ingredients on soil bags.
Soil that has been in a garden for a while will have varying nutrient levels for reasons like plants grown there that used the nutrients, if any nutrients were added, how water drains through the soil, and lots of other factors.
Just like you when you don’t get enough good food on a regular basis, plants will not thrive without enough nutrients. So pay attention to the nutrients in purchased soil and any soil you’re already using for growing plants.
Living organisms in potting mix versus garden soil
Potting mix and many of the materials used to create potting mixes are expected to be free of living organisms to prevent pathogens from infecting and harming plants or damaging seeds. Often potting mixes are heat treated to kill weed seeds and fungal spores.
Garden soil that is already in-ground is full of life and living organisms, like fungi, insects and other invertebrates, bacteria and other tiny organisms. Garden soil that you buy may have living organisms depending on the source and quality of the materials used in the blend. Because topsoil is sourced by removing the top layer of land, living organisms might transfer from the source to your garden.
Seed content
Potting mix - Pre-mixed bags of potting soil and the individual materials used to create a potting mix should contain no seeds. If you create your own mix and use homemade compost that didn’t reach high enough temperatures to kill seeds added to the compost in plant debris, you could be adding seeds to your potting soil.
Garden soil - In-ground garden soil is likely to have many seeds banked up over the years. Manufactured garden soil should be relatively seed-free, however, lower quality ingredients or obtained from questionable sources could contain seeds. Using homemade compost in garden soil has the same risks of adding weed seeds to your garden soil as if using the compost in potting soil.
How to decide whether to use potting mix or garden soil
If you’re wondering whether you should use potting mix or garden soil, here are a few things to consider, with more details in sections below.
Soil purpose can determine seed starting, growing seedlings, propagating certain plants, houseplants, container gardening, raised beds, creating or building up garden beds, spreading over large area to seed grass for lawn
Plants you will be growing the soil, and if those plants have special soil needs. For example, cacti, orchids, and rosemary and some other Mediterranean plants need soil that drains well and easily. If grown in containers, potting mix can be blended using ingredients with larger pieces to increase drainage and provide ideal soil conditions
Where plants will be grown - in containers, raised beds, in the ground
Soil volume needed - whether for containers, garden beds or larger gardens or lawn areas, volume may need to be considered when choosing whether to use potting mix or garden soil
Budget for your soil as some materials are more costly, require delivery, or larger volumes are needed
Ability to access soil and get it from the store or supplier to your home
Cost considerations
Potting mix - Buying great amounts of potting mix by the bags can be expensive. And while the bags of individual ingredients are not inexpensive, you can create larger amounts of potting mix by buying bags or bulk amounts of ingredients to make your own blends at a cost lower than buying the same volume in pre-mixed bags.
You can blend potting mix and garden soil together in different ratios to create a soil mix for containers, planters, and raised beds. Using a blended soil can lower costs by reducing the amount of potting mix, or potting mix ingredients (like perlite) purchased.
Garden soil - You can buy garden soil in great volumes, usually by the cubic yard (even in Canada), like by the dump truck load or in large tote bags, which can be much less costly than buying the same volume in bagged soil.
Buying bagged soil is a better option for smaller amounts as there’s usually a delivery fee. Alternatively, soil companies might let you pick up the soil, if you have your transport method.
As a cost comparison example, a bulk soil company in Victoria, BC sells one cubic yard of garden soil for $45 and the equivalent volume, if bought by the bag, would cost $80, $229, or $269 when looking at three different brands.
Delivery and shipping
Delivery (bulk) - Manufactured bulk garden soil suppliers generally charge a minimum volume delivery - cost depends on volume and delivery distance. If you’re wanting a several cubic yards or metres of garden soil, expect to make space for a dump truck to arrive and deposit the soil in a pile. Suppliers may sell tote bags of one cubic yard of soil, and even some larger home improvement stores sell them. If the soil is ordered in tote bags, a truck with a crane or other kind of lifting mechanism will likely be used to unload the tote bags.
Delivery (bags) - Many stores will deliver bags of potting mix or garden soil, however, check the delivery costs for the number of bags you plan to purchase. Delivery fees can increase substantially when you purchase a large number of bags, so make sure the volume ordered justifies the delivery fee.
Shipping (bags) - Bags of potting mix or garden soil can be ordered online from some Amazon, suppliers, and garden centres, though the selection of brands and types can be limited. Shipping often depends on weight and size, though a few places offer free shipping with a minimum order total.
Ordering small numbers of potting mix or garden soil bags to be shipped or delivered is generally going to cost more than ordering from or going to a garden centre or home improvement store yourself or getting someone you know to help you out with the pick up.
Size of garden space
Potting mix is better for containers, pots, planters, indoor gardens, and smaller raised beds. The weight, density, and composition of potting mix provides better drainage and keeps the containers lighter and easier to move around than if only garden soil is used.
As mentioned above, potting mix and garden soil can be blended together to reduce costs when filling multiple large containers or raised beds. Generally, 50% each of potting mix and garden soil, or a third each of potting mix, garden soil, and compost works well.
Garden soil - If you need soil for an existing garden space to build up the soil level, to create new in-ground gardens or landscapes, or for topping up lawn areas, you’ll need garden soil and not potting mix. Also, potting mix ingredients like perlite and vermiculite are expensive and not necessary or economical to use in outdoor garden spaces.
You’ll need to consider the garden size or approximate area to be covered, so you know how much garden soil to buy and whether to buy bags or bulk garden soil from a supplier.
You can calculate the volume of soil needed by multiplying length x width x depth (or height) of the garden space. If you have multiple garden areas needing soil, find the volume of each and add them together. When ordering bulk materials for delivery, companies will want to know how many cubic yards and some may ask for cubic metres of material.
What type of soil to use in a raised bed?
One great thing about raised beds is that you can generally control and understand the soil that goes in the beds and what is in the soil. Here’s a simple recipe to consider when choosing what soil to use in your raised beds. The ratios are a guideline and amounts can be approximate and the materials you use might vary slightly based on where you live and what’s available to you.
Organic Raised Bed Garden Soil
Creating the garden soil blend that works best for growing in raised beds doesn’t need to be overly complicated. This soil recipe is a great one because the materials are usually easy to find and accessible in most garden centres, soil marts, or your own backyard
50% garden soil or topsoil - buy in bags or in bulk by the cubic yard or metre
30% compost - purchased in bags or homemade/backyard compost
20% other organic materials - leaves, leaf mould, composted manure, mushroom compost, and/or worm castings.
Other “ingredients” that can be added to a raised bed that aren’t soil (yet) are branches, stumps, and twigs that came from healthy trees or shrubs and isn’t hosting any pests or diseases. Using these woody materials in the bottom of the raised bed can help by adding volume to the space, which reduces the soil blend volume needed. The materials also provide food to soil organisms, encouraging a more biodiverse and healthy soil and adding organic matter to the soil as the wood breaks down over time.
Considerations for raised bed soils
Plant choices - Raised beds can be used to grow vegetables, but also many other plants, like cut flowers, strawberries, blueberries, etc. Plants have ideal growing soil conditions, such as soil pH or how well the soil drains.
Think about the plants you’ll be planting in your raised beds and whether you might need to customize your raised bed soil blend for those plants.
Soil settling - Organic matter (sticks, bark, compost, etc.) included in the raised bed soil, or at the bottom of the raised bed, will gradually break down and the soil will settle.
Add compost or a blend of compost and garden soil to the top of soil each spring or after harvesting an area to top up the soil surface, maintain organic matter levels, and keep soil in the root zone loose.
Use a greater percentage of garden soil or topsoil in raised bed soil mix a lower percentage of organic materials to slow the rate of settling (i.e. fewer materials to break down = less material to settle)
Soil is heavy, especially when garden soil or topsoil is the main ingredient and the raised beds are large and/or deep (e.g. deeper than 60 cm or 2 ft).
Use materials and design features when building raised beds to withstand the soil volume and weight over time.
Microclimate - Raised bed soil, especially near the bed edges, will warm faster in the spring and mornings, and cool more quickly in fall and nights than in-ground soil. Because the soils warm faster, they will also dry out faster than in-ground soil.
Watch the soil moisture in your raised bed as you may have to water more frequently than plants growing directly in the ground.
Seeds may germinate and plants grow faster in raised beds than in-ground because of the warmer soil.
Nutrients - Raised bed soils drain well (gravity and looser soil material), which can lower soil nutrients levels by moving the nutrients through the soil and away from plant roots.
Add soil amendments, like compost, composted manure, or even straw, to your raised beds to maintain organic matter levels and add nutrients.
When sourcing bulk garden soil for your raised beds, be sure to check out and ask around about any places where you may buy the soil. In 2020, when people started gardening or expanded existing gardens and purchased soil in bulk, several people told me that they were so disappointed with the very poor quality “soil” they received.
Companies will include lower quality materials and rocks in their soil to create more of it to sell. It’s okay to reach out and ask where companies are sourcing their supplies and how the soil is made.
Frequently Asked Questions
What is a potting mix?
Potting mix is a blend of non-soil materials (e.g., peat moss, compost, perlite) that is used like soil for growing plants in. Potting mix, also known as potting soil, is available in pre-mixed bags for specific plants and uses, like for house plants, or special blends for seed starting. Potting mix can also be blended in larger volumes by purchasing the ingredients separately and combining in desired ratios, which depend on the use.
What is garden soil?
Garden soil is either purchased in bags or bulk as a mix of topsoil, mineral ingredients, such as sand or loam, compost, and maybe other ingredients, like peat moss and/or organic fertilizers. Garden soil is also the earth material found in your existing gardens or yards. Garden soil blends can also be customized for specific plant types, like vegetables, or garden styles, such as raised beds.
When do you need to add nutrients to your soil?
Nutrients may need to be added to potting soil more often than garden soil because the potting soil is usually more free-draining and lower in organic matter to retain nutrients. Extra watering required for such soil can cause nutrients to be reduced. Adding nutrients to your soil can also depend on the kind of plant grown because certain plants have higher nutrient needs.
Can you put potting soil in a garden bed?
You can put potting soil in a garden bed, if you have some left over when containers need emptying and it’s known to be disease and weed-free. To use potting soil to create or build up garden beds would be potentially quite expensive and unnecessary if there's already soil in a garden bed. If you want to create a garden, garden soil is a better idea. Topping up the garden soil with materials like compost is more beneficial because it adds organic matter and improves the soil rather than adding potting soil.
What is the best soil for container gardening?
The best soil for container gardening is potting soil with compost mixed in. The compost will add organic matter, which will improve the ability for the nutrients to be retained in the soil. You can improve the potting soil for container gardening by mixing in other ingredients, like worm castings or other amendments containing nutrients.
