Dishing the Dirt: What Every Gardener Needs to Know

If you’ve ever found yourself wondering what exactly the difference is between compost, manure, soil, potting mix, leaf mould, peat moss and so on, you’re not alone! These terms get used interchangeably all the time, yet each one plays a very different role in the garden.

I’m going to break down what each of these materials actually is, and how you can use them to get the best results. By the end, you’ll know what to use – and where – to build healthier soil and grow happier plants without wasting your time or money. Let’s dig in!

What Is Soil?

Let’s start at the very beginning, with soil itself. This divinely delicious dirt is literally the root of all life. It might not look like much, but it’s a living, breathing ecosystem made up of mineral particles such as sand, silt and clay; organic matter from dead and decaying plants and animals; air, water and various nutrients; and, perhaps most magically for us gardeners, a truly bustling community of organisms, including worms, bacteria, fungi, beetles and more. Together, this creates a dynamic environment that supports our plants.

Few soils are perfect. Very sandy soils might drain too fast and dry out quickly, while heavy, claggy clay soils can stick to your boots like glue. But every garden soil will benefit enormously from the addition of more organic matter.

Organic matter is anything made from once-living things, and will help to improve the texture of soil while feeding all the life it contains. Whether your soil is sandy, silty or clay, organic matter will help plants access nutrients and makes soil more resilient to both wet and dry weather, buffering it against extremes.

And that’s where organic matter like compost, manure and leaf mould come into play…

Compost

Regular viewers will have heard me bang on about compost a lot, but that’s for a very good reason: compost is one of the very best ways to improve garden soil.

Compost is made from broken-down organic materials such as, for example, vegetable peelings, garden trimmings and grass clippings, coffee grounds, old weeds, bedding from herbivorous pets or chickens, and countless other materials.

Through the magic of microbes, fungi and other compost-dwelling organisms such as worms, these raw materials gradually transform into the dark, crumbly, earthy-smelling goodness that is compost. Think of it as your soil’s equivalent of a hearty, home-cooked meal. It may not be flashy, but my goodness doesn’t it make everything feel better! Compost is first-rate at improving soil structure, feeding soil organisms and slowly releasing nutrients so they’re available for plants. It’s safe to use anywhere in the garden.

I like to spread compost in a layer an inch or so (2-3 cm) thick over my beds at least once a year, typically any time from late autumn through winter when most beds are generally emptier, or in early spring before planting. I also add it around actively growing crops in the warmer months, when this magical mulch will help to shade the soil and keep plant roots cool.

Organic matter (and some non-organic materials, like weed fabric) laid on the soil surface is known as mulch, and adding it (funnily enough!) is known as mulching.

Traditionally, compost was dug into beds, but that’s a lot of hard work and not great for the back, so I don’t bother! Mulching involves less work for me, avoids tearing at the delicate soil structure, and it gives the worms something to do over the colder months as they pull it all in for me.

No matter how you use it, compost helps your soil steadily improve over time. It’s one of the most powerful tools any gardener has.

Manure

You’ll find some passionate opinions about manure! The manure we use in our gardens comes from herbivores such as horses, cows, sheep or chickens. Fresh manure straight from the source is potent stuff, loaded with nitrogen and other plant nutrients – the food that plants need to grow strong and healthy.

That’s all great, but fresh manure is a little too rich, and spread around growing plants it can risk scorching tender roots. Fresh manure is a bit like a very energetic toddler – full of potential but absolutely not something you want near delicate plants!

Instead, the best manure to use is aged, or well-rotted manure. It will have been stacked up and left to mature, like a fine wine, for several months. It’s dark and crumbly, doesn’t smell especially strong, and there are hardly any bits of straw or other bedding materials in it.

Well-rotted manure behaves a lot like compost and can be used in a very similar way. Like compost it’s fab at replenishing soil nutrients, boosting microbial activity, adding more organic matter and, of course, improving your soil’s structure.

It’s really powerful stuff, full of the nutrients plants need, so I prioritize using it in the areas where I’ll be growing especially hungry crops like cabbage-family plants, squashes, or corn.

But be careful where you source manure from. It must be free of any traces of herbicide. Persistent weedkillers like aminopyralid can remain in manure from animals that ate either contaminated hay or grazed on treated pasture. These herbicides can stay active for years and will harm any sensitive crops like tomatoes, beans and potatoes that are growing in it. So always ask about herbicide use before sourcing manure, or test a small batch before spreading it more widely in your garden. Better safe than sorry!

Leaf Mould

Leaf mould (rotted-down tree and shrub leaves) is one of the most underrated materials in the garden, in my humble opinion! Leaves break down differently from most other composting materials because they’re high in lignin, which is a tougher plant fibre. This means leaves rot slowly, mainly with the help of fungi rather than bacteria.

Leaf mould is incredible at holding onto moisture and boosting beneficial fungal life in the soil, while creating a soft, crumbly soil texture that helps with drainage and makes it easier for plant roots to travel. Nutritionally it’s relatively low, but that’s absolutely fine. Think of leaf mold as an excellent soil conditioner, improving soil structure, rather than as a fertiliser.

Like compost or manure, I use leaf mould as a mulch on beds or around plants – any time I want to give the soil a bit of a boost. Because it’s fairly low in nutrients, this actually makes it perfect for making my own seed starting potting mixes. Tiny seedlings don’t need much in the way of nutrients, so leaf mould is perfect for getting them started, and by making my own mixes I can save a bit of money.

The best thing about leaf mould, though, is that it’s completely free! Every autumn the garden rains down a whole new bounty of leaves – all you need to do is rake them up and stack them away to slowly rot down. Simply pile them up in a cage made from wire mesh or old pallets and forget about them for a year or two. Nature will do the rest. After a year chilling out in the cage, you’ll have a fantastic soil improver, and after two years something even crumblier for making those fine-grained seed starting mixes. Absolute gardener’s gold!

Potting Mix

Next up: potting mix. And this is where things can get a little confusing! Depending on where you are in the world you might call potting mix ‘potting soil’, ‘potting compost’ or, simply, ‘compost’ (but this is very different from the homemade garden compost we looked at earlier).

Potting mixes are specifically formulated for growing plants in containers. This is because plants in any kind of container need a lightweight and airy growing medium that will retain moisture yet still be free-draining. It might be tempting just to dig up some soil from the garden and use that in containers, but soil is usually too heavy, dense, and just too variable. In pots it can compress down, starving roots of air, which is why specialised potting mixes are so valuable for container-grown plants.

Potting mixes are typically made from a combination of materials such as composted bark, green waste, coconut fibre, sand or grit, perlite or vermiculite, and often added fertilisers. Some mixes also contain peat, though many gardeners now opt for peat-free mixes to protect fragile peatland habitats (more on that shortly).

Seeds and very young seedlings thrive in a fine-textured, low-nutrient potting mix, and you can find tailor-made mixes specifically for this purpose sold as seed-starting mix or seed compost.

More mature plants need something a little richer and with a better structure, typically sold as all-purpose potting soil or multipurpose compost. This general-purpose mix is also good for most seeds and seedlings, especially if screened to give a finer texture, and it’s generally a lot cheaper than specially formulated seed-starting mixes.

Peat/Peat Moss

Peat and peat moss has long been used in gardening because it’s good at holding moisture, is fluffy in texture and is naturally sterile, making it a great foundation to build on. But extracting peat has a huge environmental cost. Peat takes thousands of years to form and peatlands are precious: they support unique wildlife and act as massive carbon stores. So when peat’s harvested, all that safely stored carbon escapes into the atmosphere, and fragile ecosystems are destroyed too.

Try to avoid using peat if you can, and check that any potting mixes you buy are peat-free.

Thankfully, there are alternatives. Coir (coconut fibre), a by-product of the coconut industry, is my favourite. It’s got a similar texture and properties to peat, and it’s renewable and widely available. This is just the job for making your own potting mixes, for example mixing it with an off-the-shelf potting mix and a little perlite to create the perfect light, fluffy growing medium for plants like peppers. Or blend it with compost or leaf mould from the garden to make your own seed starting mix that’s much cheaper than bagged mixes.

Woodchips and Bark Chippings

Woodchips are made from freshly chipped trees and branches, while bark chippings, which are arguably more decorative, mainly consist of only the outer bark. Woodchips and bark chippings are not ideal for digging into soil because their high carbon content causes microbes to ‘steal’ nitrogen from the soil to help break them down, which can make it harder for plants to grow well. But they are fantastic when used correctly.

I use them to mulch around perennial plants like fruit trees and bushes where they will rot down slowly over time to give long-term soil improvements. They are great at boosting soil fungi, which will in turn will help with plant health.

I also love using them to surface paths, keeping them weed- and mud-free. Even here they’ll help to sustain plants in nearby beds as roots reach down and out under the paths. As woodchips or bark chippings break down slowly, they create a gentle, sustained release of nutrients — perfect for slow growers.

Woodchips and bark are also great for layering with greener, nitrogen-rich materials or manures to create a powerhouse of lovely compost.

Organic Matter Comparison

So let’s sum up the differences so you can choose the right organic matter for the right job:

Understanding the differences between all these materials will unlock so much potential in your garden. Not only does it help you nurture healthier soil, but it also enables you use your resources more wisely – how satisfying!