Module 12: Compost Basics

When planting and growing anything in the garden, one word you may often hear is ‘compost.’ While you may know what compost generally does, there may be questions about what compost is or how to use it properly. There are many different types of compost, and all can be used in different ways and for different plants – most of the time, it’s not a ‘one-size-fits-all’ situation, though there are a lot of useful all-purpose or multi-purpose composts, sometimes you will need additives to make the conditions just right for whichever plants you choose to grow. 

What is Compost?

Compost is a soil additive created from decomposed organic matter, which is normally regarded as waste. The process of composting takes this organic matter and reduces it over time to create a soil conditioner (compost) which can then be applied to all sorts of plants to encourage rapid, healthy growth and improve the overall soil quality. It also helps recycle brown and green waste – mostly using a compost bin – and makes the perfect fertiliser due to the composting process retaining all those nutrients.

Which Compost Should You Use?

Compost is beneficial in many ways, as being able to use compost means that you don’t have to worry too much about the condition of your existing garden soil. Of course, it is good to find out what type of soil you have before beginning, but adding compost to this soil can change the fertility of the soil and its overall composition. There are many different types of compost which all do different things and have different properties, so they are recommended for different plants entirely.

Here are the five main types of compost:

1. Peat Compost

Peat compost has been used for years for many different purposes. It is a naturally occurring substance made from decaying vegetation – mostly from sphagnum moss or sedge. While naturally low in nutrients, it provides an aerated, warm environment for roots to grow in. This medium can hold moisture and nutrients while preventing the roots from getting too waterlogged, perfect for avoiding complications that many plants get from root rot. 

Most peat compost mixes will have other additives to add nutrients or texture for added drainage. Commonly, you will find a peat compost mix with sand, grit, vermiculite or perlite and a range of added nutrients, too. The exact ingredients used to make the peat compost mix available will vary depending on its target use. There are peat compost mixes that will benefit your plants as seeds and some that will keep mature plants growing strong, though many people are shifting from using peat-based composts as there is an environmental impact to be considered. 

Peat is found in lowland bogs. Using peat from these peat bogs on a large scale (such as in the Horticultural industry) can damage those wetland environments. The main issues come about when we use more of this naturally occurring peat than is being replenished, similar to many naturally occurring resources. This has led to many companies offering peat-free alternatives or peat compost mixes with lower peat content. 

2. Loam Compost

Loam compost mixes contain a certain amount of loam soil in their mix, whereas many compost mixes contain no soil at all. Loam soils contain an even balance of minerals. These loam soils are composed of 40% sand, 40% silt and 20% clay. The benefits of these components can really help with the growth of some plants. Sand is good for aeration and drainage but doesn’t do too well for water retention, which is why a good balance with silt and clay helps. Clay particles in the soil are tiny and compact well while generally being nutrient-rich, whereas silt is less nutritious than clay but retains moisture well. 

Some of the main reasons loam compost is highly recommended are that it retains nutrients and water well while still being well-draining. This means that the roots will be kept moist while reducing the risk of root rot. These types of compost are especially good when used in a vegetable garden or for mature plants that will stay situated for a long time. It is always important to remember that with loam-based composts, a lot will have a different makeup, with different additives and nutrients added. As such, this means that not every loam compost is good for every type of plant, and this is something to be wary of before planting up all of your plants in a loam compost. 

3. Peat-free Compost

As mentioned above, many gardeners and horticulturalists are trying to avoid the overuse of peat that we have seen in recent years. This is due to the lack of sustainability with the use of peat compost. Thankfully, in more recent years, there has been an influx of peat-free alternatives to aid those gardeners who wish to plant their gardens more sustainably. Peat-free compost refers to any compost which does not contain peat moss, though some peat-free alternatives are used specifically to try and recreate the properties of peat compost. 

Some of the materials added to compost as a peat substitute are a perlite, a volcanic glass that expands and becomes porous in higher levels of heat; coconut-based materials, such as coco pulp which has similar properties to white peat and can help aerate the substrate. Other alternatives are being used, such as bentonite or expanded clay – bentonite is also a clay mixture – and wood fibre or chips. All of the alternatives are also naturally sourced, though it is generally reported that they do not impose such a risk to the local wildlife when being sourced. 

4. Organic Compost

Organic compost is generally what most new gardeners will think of – this is the compost that you can make at home and holds a lot of nutrients which is extremely beneficial for aiding in the growth of your plants. These composts comprise rotted organic materials or green waste, such as fallen leaves, grass clippings, and more or brown waste, such as food scraps. The best way to make your organic compost is in a compost bin, just by adding any of your garden or food waste each time you find some leftovers lying around. 

The benefits of using organic compost – even better if you’ve made it yourself – are that the nutrient levels tend to be a lot higher than a generic compost due to the composting process, which may not necessarily retain as many nutrients. This can mean you won’t need to worry as much about adding feed or fertiliser. The organic matter in the compost can also retain water well while keeping the substrate aerated which can help the nutrients travel further. These composts can boost soil fertility, reduce greenhouse gas emissions and provide crops with an extra boost from organic matter. 

5. All/Multi-Purpose Compost

All or Multi-Purpose composts are generic mixes with a well-balanced mix of nutrients which are generally beneficial to most plants, though if you have plants growing in your garden that may need a more specialised mix then it is usually best to have fertiliser or feed on hand as well. This can ensure that you are giving your plants everything they need. That isn’t to say that you can’t use multi-purpose compost alone; you need to ensure you know that each plant you are growing will need to grow to its full potential. 

Multi-Purpose composts are found in most garden centres, and each will have a different composition, so be sure to check the contents and ingredients before using them all over your garden, as you may need to think about what else you can do to boost the properties of your soil. These composts are especially good for topping new raised beds, mulching existing beds or borders and filling containers of plants with no real specific requirements. 

Making Your Own Compost

With the cost of living rising and the call for change in climate change and environmental factors, one of the best ways to cultivate your green thumb on a budget is to start making your own compost. Compost can enrich the soil your plants grow in, aiding in growth and, where edible plants are concerned, a higher crop yield. Composting doesn’t have to be a mystery, and it can help reduce your waste output, reusing and recycling all of those green and brown materials that may have previously been put in the bins for collection. 

Why bother?

Most councils offer green waste and brown waste collection services, though if you can start composting, this will reduce your environmental impact further. Bin collections are associated with heavy transportation and other environmental impacts, so if everyone were to start turning their food scraps and garden cuttings into compost, this would lessen the impact we were having on the environment, which is at the forefront of many people’s minds these days.

When to Compost

Composting can be done all year round, as there will never be a shortage of materials you can use on the compost pile or in the compost bin. Suitable materials for composting include fruit and vegetable peelings, grass cuttings, fallen leaves and other green and brown materials, all of which are known as organic matter. The key time of year for composting is late summer to early winter, though, as temperatures are high in the late summer, which will accelerate the composting process, and grass clippings, fallen leaves and more can be added to the compost in the autumn/early winter to boost the nutrients. 

How to Compost

When starting compost heaps or compost bins, there are a few things to remember. The location and container can really aid or hinder the composting process. Bins will help retain warmth and moisture, speeding up the breakdown of organic materials like your food scraps or grass clippings. However, open compost heaps will do the trick. Eventually, it will just take longer as there is less temperature regulation. If you did decide to use a compost bin, any of the marketed compost bins available will work, as long as they keep out the rain, keep in some warmth and allow drainage and aeration. 

If you really wanted to DIY the composting process, you could even build your own compost bin or container out of wood. 

What to Add to the Compost Heap

Many people will think that just chucking everything on the compost heap will do the trick, though there are a few things to be mindful of when making your own compost. Balance is key when it comes to any soil additive or compost; this is the same for homemade compost made of organic materials. 

When adding green materials such as grass clippings and food scraps to the compost pile, these will contain higher levels of nitrogen which will speed up the composting as they heat up the pile and accelerate the breakdown of the materials. Nitrogen is also good for growing plants as it will aid in photosynthesis, giving a better green pigment to the growing plants.

Brown materials, on the other hand, are more carbon-rich. These materials will include dry leaves, twigs, plant stalks and more – all the rest of the garden waste. Adding these to the compost pile will provide food for the microorganisms in the composting process to consume and digest. The carbon content in compost will also affect plant growth in that it can result in healthier and more productive plant growth. 

Compost piles also need moisture and oxygen. Water will help the materials break down, and oxygen will regulate the temperature, eliminate some foul odours and break down any pesticides used on the garden waste before adding to the compost pile. 

When is it Ready?

Composting can take six months to 2 years to be ready. Turning the heap will also enable you to see when it is ready. When it is done, you will find a dark brown, crumbling soil-like substance which smells like damp earth. 

You will find that, over time, there will still be some un-rotted organic materials in the compost heap or bin, but this is nothing to worry about. Any matured compost can be removed and used in the garden, while any remaining materials can be left in to break down further. 

Leaving the un-rotted materials in there and adding more food scraps and other organic materials will eventually give you a steady flow of compost production, especially if you make sure to get that perfect balance of brown and green materials previously mentioned.

Coming Next

The next stage of our course is Module 13 - Hardiness Ratings Explained

Further Reading

Compost: How to choose the right type

Homemade Composting: The Benefits & How to Make Your Own