Tony O’Neill, gardener and author of the popular “Composting Masterclass” and “Your First Vegetable Garden,” combines lifelong passion and expert knowledge to simplify the art of gardening. His mission? Helping you cultivate a thriving garden.
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When researching the differences between potting soil, topsoil, and garden soil, it became apparent that each has particular uses. This article will go into the details of how these variations of soils differ and why.
The main difference between potting soil, topsoil, and garden soil is that it’s been specifically formulated in containers. Topsoil is usually processed to become finer, making it perfect for raised beds and seeds. Finally, garden soil is topsoil enriched to make it optimal for plant growth.
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In terms of usage, potting soil is used to aid the growth of particular container plants.
For example, there are variations of potting soil mixed with other materials and nutrients to make them ideal for the growth of cacti, herbs, vegetables, or other plant species that can be grown in a pot.
Topsoil is simply the uppermost layer of soil. Sometimes, topsoil is the name given to soil subjected to a process of filtration or screening to remove lumps and make the texture as consistent as possible.
Garden soil is a variation of topsoil. Combine it with other organic matter or even compost to make it better suited to promoting garden growers’ growth.
“Like the soil, the mind is fertilized while it lies fallow until a new burst of bloom ensues.”
John Dewey
Potting soil – everything you need to know
In the following section, I will explain what potting soil is, what it is used for and why it’s such a useful variation of soil for gardeners.
Technically, potting soil is a collective term used to describe numerous variations of soil. Still, these soils all have one thing in common – they are specifically formulated for potted plants and container growers to thrive.
What ingredients are in potting soil?
Let’s get into the ingredients commonly found in potting soil. A natural, raw, age-old peat is one of the most commonly found components in potting soil.
It originates from plants’ remains and is a brilliantly effective ingredient for nourishing them. One of the main reasons peat is included in potting soils is its exceptional ability to absorb moisture.
Not only is it greatly absorbent, but it also retains moisture well. Another reason peat is commonly used within potting soil is that it stimulates growth.
Another ingredient you will find in potting soil is called coir. For particular plants, coir and peat are mixed, and sometimes compost, fertilizers, sand, and lime are included.
All of these components are put into potting soil because the mixture creates the perfect PH level of acidity for the specific plant that thrives in that environment.
They also create a densely nutritional matter with the appropriate amount of fertilizer, giving the plant the best chance of growing healthily in the potting soil.
The plant roots soak up the mixture’s nutrients and grow into a strong, healthy adult plant species.
As I previously mentioned, the ingredients in potting soil have been purposefully included for the specific plant type they intend to use. Another commonly used material, along with peat, is pine bark.
Pine bark is used for its ability to add moisture to the potting soil. As a bonus, it also helps to retain fertilizer and adds air space.
If you were to use bark on its own, it wouldn’t provide any benefits to plants, but after it has been put into potting soil with peat, it enhances the mixture by extending its longevity and making it harder to break down.
The final ingredients in potting soil worth noting are perlite and vermiculite. These two matters originate in volcanoes and are included in potting soil because they greatly improve the material’s aeration properties.
Why is potting soil lighter than topsoil?
They also make the potting soil lighter, which is important because dense and heavy soil is no good for growing many plants.
One of the dangers of perlite is that it can collect fluoride if water that contains it is used on the plants.
This can result in certain houseplants being damaged at the leaf tips. On the other hand, Vermiculite is more useful, as it can hold water and fertilizer nutrients for some time.
So potting soil is a mixture of the organic matters we’ve just discussed, with added fertilizers for nutrients. It’s tailored to suit specific plants, so if you have a container grower, you can most likely find suitable potting soil with all the necessary nutrients and ingredients to encourage it to thrive.
What is topsoil?
Next, let’s take a detailed look at topsoil. If I were to define topsoil, I’d say that it is the upper layer of soil known to be highly nutritionally dense and contains a lot of organic matter.
You can buy topsoil from most garden suppliers or DIY stores, probably the most common type of soil used among gardeners.
What are the uses for topsoil?
One of the main reasons a gardener would need to get topsoil is if the pre-existing soil in your garden was in poor condition or if you didn’t have access to natural soil in that area.
New built homes and patios are examples of locations that may have had the natural topsoil removed for construction. Say, for example, you have a paved garden; topsoil would be a brilliant option to be used in raised beds to grow plants despite a lack of natural soil.
We can break down topsoil into three categories, or as commonly referred to, grades.
What is topsoil made from?
These grades are called: premium grade, general-purpose, and economy. You can find the attributes of these three grades listed below.
Premium Grade
Is probably the most expensive topsoil, but the price reflects the quality. This soil is guaranteed not to transport the seeds of weeds into your garden.
It is highly fertile and has a great structure for building new flower beds. It is also commonly used by nurseries to be added to potting soil mixes.
General Purpose
Is available in different consistencies depending on what you need to use it for. Like premium grade, it too is effective for usage in new flower beds or can be used as the underlayer for a new lawn to be laid on.
Some of the more coarse varieties are especially handy for laying turf, but the finer consistencies would be better suited to the top dressing of your lawn.
The Economy
Lacks the quality of the two previously mentioned grades of topsoil. Still, it is useful for filling in large volumes of the area where you need quantity rather than quality.
Garden soil uses and ingredients.
Finally, let’s discuss good old garden soil. You may have seen large bags in the local garden center labeled as garden soil, and these are usually pre-mixed products that have been made to add to the soil that already exists in your garden.
Like potting soil, garden soil ingredients depend greatly on what you intend to grow in it.
For example, varieties of garden soils intended for vegetable growth will have a different PH and nutritional profile compared to those for growing daffodils.
Garden soil is made to be tilled into your existing soil in flower beds. Mixing garden soil with compost at 25% to 75% is common among gardeners as this creates a generally good growing environment for most plants.
Gardeners also use garden soil to describe the existing soil in their gardens. This soil is vitally important in deciding how healthy your plants will grow.
You could even say that the health of a garden is simply a reflection of the health of its soil. Let’s look at this definition of garden soil, its varieties, and its materials.
A great way to determine your garden soil’s quality before planting is to dig up a scoop and analyze its texture. Is it light and well aerated, or sense and heavy?
The texture of the soil is an indicator of the mixture of minerals and particles it contains. The four most common materials in garden soil are clay, silt, sand, and loam.
But the ratio of these ingredients can vary widely, affecting its growing capabilities, texture, ability to hold nutrients, and draining capacity.
Ultimately each type of garden soil has its advantages and disadvantages:
Clay soils
Clay comprises minute, densely packed particles that hold large quantities of water and nutrients.
However, this garden soil variety has drawbacks – it drains quite slowly and can become solid when dry.
Sandy soils
Sandy soils are composed of large particles that allow moisture to pass through them easily, but vital nutrients are also lost in this process.
Silt soils
Silt soils are made of wonderful particles tightly compacted together, which can negatively affect aeration and drainage.
Loam soils
Loam soils are arguably the best-suited type of garden soil for most plants, as they are made up of a good balance of minerals and full of goodness left behind when an organic matter has decomposed.
Soil & PH Levels
One of the most important factors to consider with potting soil, topsoil, and garden soil is their PH levels. This is imperative because it indicates how fertile the soil is.
Potting soils will be perfectly formulated to have the ideal PH level for the plant intended to be grown in them. Topsoil and garden soil are less predictable, though.
A good rule of thumb is that certain nutrients will become unavailable to your plants if your soil is too alkaline with a PH level greater than 7.5 or too acidic with a PH level less than 5.5. This can cause major issues for their healthy growth.
Most plants are resilient enough to handle variations in PH levels. But most prefer to be grown in soil with a PH somewhere between 6 and 7.
This soil is slightly acidic; therefore, it allows vital nutrients such as potassium, calcium, magnesium, nitrogen, and phosphorus to dissolve into the soil and be absorbed by the plants.
If the soil swings too far in one direction of acidity or alkalinity, the plants may only get some nutrients and be deficient in others.
Helping your soil with organic matter
The four types of soil we are discussing in this article all have in common that they all benefit from adding organic matter. In sand-based garden soil, organic matters work to improve its capability of holding water and how well it can retain nutrients.
In clay garden soil, the organic matter loosens up the minerals, which is useful because they become sticky when the soil gets wet and harden when it dries.
Organic matter supplies the soil with slow-releasing nutrients, which plants love. Organisms within the soil also benefit from it.
As time goes by, soil that the addition of organic matter has amended will provide all of the necessary nutrients your plants need and reduce the need for fertilizer use.
To get the best out of soil amendments, you should add them to your potting soil, topsoil, or garden soil in the autumntime. This will ensure that they have decomposed enough before you plant your next batch in the springtime.
To mix the organic matter properly, using a garden fork to mix the materials into the top 5 inches of your soil mix is essential. If your potting soil, topsoil, or garden soil is mainly used to grow vegetables, you can add organic matter at the start of every season.
If you intend to grow perennials predominantly, add the organic matter to your soil before planting them, so the plant roots don’t get disturbed.
Most perennials have to be dug up every couple of years for division purposes, so this is the perfect time to add your organic matter into the mix.
Conclusion
To conclude, regarding the differences between potting soil, topsoil, and garden soil, you must establish your intentions regarding your garden.
Suppose you would like to grow container plants, vegetables, or herbs predominantly. In that case, you need to get a particular variety of potting soil mix to enhance these plants and improve their growing environment.
If you are more focused on flower beds and improving your garden’s existing soil, then topsoil is most likely the right choice for you.
There are many options for topsoil, so again, knowing what you intend to grow is essential to ensure you choose the right variety.
Topsoil improves the soil’s overall health, so it’s always good to have some in supply.
Finally, garden soil is what you probably already have in abundance. Determining this soil’s quality and consistency is vital to know what you can and can’t grow effectively in your garden.
Adding organic matter, as previously discussed, is a great way to improve its qualities if your garden soil is in poor condition.
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