One of the most confusing issues for new or inexperienced gardeners is which compost or potting mix to choose for different jobs around the garden. This can sometimes seem rather confusing when you are new to growing your own. But if you remember a few basic things, it is difficult to go too far wrong. So to help you understand the options, and which one you need, we’ve put together this basic guide to lead you in the right direction.
Types of Compost or Potting Mix
First of all, it is useful to take a look at the different ways that compost and potting media are used in a garden. They can be used:
As a mulch on garden beds or borders, to amend and improve the soil and keep up fertility over time. (Traditionally, they were often dug in. But in a no dig garden, it is best to leave the soil as undisturbed as possible, keeping digging and tilling to a minimum.)
To fill (or top off) raised beds. Building layers of organic material to compost in place, then potting beds with a thin layer of compost/ potting mix can be a good way to make new growing areas more cheaply. And to make use of natural materials at your disposal.
For sowing seeds into in seed trays, flats or pots.
To fill containers and planters in a container garden.
So, let’s take a look at the different types of compost and potting mix that you might use in your garden and where they might be used. We’ll take a look at:
Multi-Purpose Compost (Peat Based or Peat Free)
Seed Starting Compost
Potting Media For Container Plants (Soil Based or Soil Free)
A homemade compost can and should be a key feature of any organic garden. Setting up a composting system to process kitchen scraps, other compostable material from you home, and vegetative matter from your garden should be a top priority.
It is important to understand, however, that a homemade compost is not the same as a compost or potting medium that you can purchase online or from a garden centre or shop. A compost differs from a potting mix because a potting mix is a combination of different materials which has been carefully created to optimise growing conditions for plants.
Homemade compost is great for adding as a mulch on growing areas. And for enriching the soil in your garden. But if you want something to fill pots and containers, it should usually be combined with other materials for best results. (More on making your own potting medium can be found later on in this article.)
Multi-Purpose Compost (Peat Based or Peat Free)
If you are buying a compost for your garden, then it is important to understand the different options available. Multi-purpose or all-purpose composts are designed to make your life easier – since they are formulated to make them suitable for a wide range of garden jobs.
Multi-purpose composts can be used to amend the soil, as a mulch. They can be used for filling raised beds, planters or containers. And sometimes, they can even be suitable for seed starting.
It is important to understand, however, that not all multi-purpose composts are created equal. Some are far better quality than others. Often, even those which are purportedly for all the above uses will not necessarily give the best results.
Multi-purpose composts are formulated to provide suitable growing conditions for a wide range of different plants. But it is important to consider which plants you wish to grow. Since some will require different, specialist compost formulations. For example, if you wish to grow acid-loving plants, then a special ericaceous compost may be required. Other plants may need a specialist, more free-draining medium.
Peat Based or Peat Free
Multi-purpose composts can be broadly divided into two main categories – peat based and peat free. Peat based options contain peat – from peat bogs. But in an eco-friendly organic garden, peat based options should always be avoided. Using peat in our gardens does great ecological harm. It contributes to the destruction of precious peat bog ecosystems. Systems which we need for carbon sequestration, biodiversity, and for our water cycle. So if you want your gardening efforts to be as sustainable and eco-friendly as possible – always choose peat free options.
Rather than using peat, peat free formulations rely on other natural ingredients to provide suitable fertility and growing conditions. Peat free formulations may contain a proportion of green waste. They often also include coconut coir, or woody materials (well-rotted wood chip etc.). And may also contain ingredients like bracken, sheep’s wool etc..
Another thing to think about when choosing a multi-purpose compost is whether the mix is organic, or contains other materials which may be harmful to the environment. Some mixes, for example, may contain things like synthetic fertilizers, which pose a risk to natural environments. These are obviously also to be avoided in a sustainable and eco-friendly organic garden.
Seed Starting Compost
A multi-purpose compost may be great for mature plants. But might not provide optimal conditions for seed starting. While you can create your own seed starting mix, you can also consider purchasing specific formulations designed for seed starting.
A mix for seed starting is typically a light, aerated and friable mix, with small particle size. It should be relatively free-draining, yet retain sufficient moisture. It does not need to be as rich in fertility as a mix in which plants will remain during their lifecycle. Or for composts which are to be used as mulch in your growing areas.
Potting Media For Container Plants (Soil Based or Soil-Free)
Many formulations that you can buy are specifically designed for use in containers or pots. These mixes can provide suitable growing conditions for a wide range of container plants. Potting mixes can be soil (loam) based, or soil free. Soil based potting mixes (John Innes) contain sterilised loam and there are different formulations suitable for different plants which are well tried and tested for different applications. But soil free options are also available – often containing coir or other natural materials.
You can also consider making your own potting mix/ compost for containers. You can make a soil based mix, or a soil free formulation yourself at home.
One of the simplest options for filling pots is to take around 1/3 friable loam/ good quality garden soil, 1/3 homemade compost, and 1/3 leaf mould, and using this to fill your pots. I like this option since all three ingredients are ones which can ultimately, long term, be sourced/made at home, using ingredients from your own home and garden.
The problem with DIY soil based potting mixes is that they can harbour fungi, and weed seeds which may pop up. If this is an issue, you can consider sterilising the soil/ loam in your oven. But this is not always necessary.
Soil free media can also be made at home, using well-rotted woody material, or ingredients like coconut coir. There are a number of different recipes which can be considered to meet the needs of a range of different plants that you may wish to grow.
Do you have a favourite compost/ potting mix recipe to share? Any tips of your own? Let us know in the comments below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.