How to Make Your Own Potting Compost and Why Regular Compost is Your Worst Enemy
A simple step-by-step guide to potting compost
Save time and money whilst growing healthy plants that’ll thrive
Created by the team here at DIY Gardening
Welcome to our Soil and Compost section of the DIY Gardening website!
Potting compost; what is it? How is it different from regular compost? Do you really need it or is it just part of another marketing tactic?
If you’re new to gardening or perhaps a regular who’s never used potting compost before, this guide is for you.
What is Potting Compost?
Potting compost is a light, well-draining growing medium designed specifically for plants grown in pots.
There are several types of potting composts:
- Seed potting compost.
- Potting compost for young plants.
- Potting composts for established pot plants.
All three types of compost are very different from regular compost or garden soil which is too heavy and dense for most pot plants.
There isn’t much difference between the three compost types as all are light, well-draining, well-aerated mediums that allow roots to grow strong and healthy.
What’s the Difference Between Potting and Multipurpose Compost?
Multi-purpose compost is a nutrient-rich growing medium that can be used as a standalone material to feed established plants for up to a year. It can also be deployed as a soil conditioner.
Most potting composts contain fewer nutrients than multi-purpose composts but have better drainage and are more aerated – perfect for seeds, cuttings and plugs. Do remember that a light airy growing medium will allow roots to grow while dense heavy soils and composts restrict the early root growth.
Perhaps the image below will help to explain:
When growing young plants (ie from seed, cuttings or small plugs), it’s essential that the growing medium isn’t waterlogged or allowed to dry out, either can lead to early failure of the plants.
It’s very easy to overwater or underwater a new plant but potting compost is far more forgiving. The extra additives can soak up any excess water so the roots don’t rot. In dry conditions, the additives slowly release the moisture thus watering the plant via the roots.
Regular multi-purpose compost is best for established plants, it contains more nutrients (which larger plants obviously need) but becomes so dense and can hold so much water, it’s not very forgiving to seeds, cuttings and small plugs.
Potting compost mixes are also perfect for both indoor and outdoor pot plants, in fact, almost all pot plants do better in aerated mixtures compared to heavy composts and soils.
What You’ll Need
Here’s what you’ll need to make your own potting compost:
Compost – We prefer to use our own compost where possible, if we haven’t got enough, we’ll mix it with bags purchased from the garden centre. If you’re new to composting, check out our list of the best compost bins, which includes a couple of products for those of you with small gardens. Ideally, the compost should be fine and fluffy, sieve out any large lumps as required.
Worm Castings or Manure – Worm castings are literally worm poo and are bursting with nutrients. Manure is a nutrient-rich organic farm animal dung and is usually from cattle and horses. It’s very dense and heavy hence why we need to mix it with other ingredients to lighten it up.
Perlite – This material is a volcanic glass that’s heated to over 1500°c where it expands like popcorn and becomes very absorbent. Perlite holds water and air bubbles so is used in potting mixes to prevent soil compaction. It also aids drainage and at the same time prevents the soil from drying out too quickly.
Horticultural Grit/Course Sand – Added in small amounts to improve drainage and create air bubbles in the mixture, it also prevents compaction.
Coconut Coir – Made from the husk of coconuts, this material is used in potting mixes as an alternative to peat. It doesn’t have any nutritional value of its own but is very absorbent. It’s also light and fluffy and holds up to 1000 times more air than typical garden soil. These qualities make it perfect for mixing with dense compost and soils. Coconut Coir is widely used in hydroponics and many plants grow in it without any compost, soil, manure or any other growing medium.
Slow Release Fertiliser – Granules that release nutrients reduce the risk of over fertilisation and are perfect for the lazy gardeners too.
How to Make Your Own Potting Compost
Here are three different mixtures, one for seeds and cuttings, one for annual plants (that’s plants you expect to keep for one season only) and the last mix is for established pot plants:
Seed Potting Compost
This mix is light, airy and well-drained, perfect for seeds and cuttings that won’t need as many nutrients as larger established plants:
- 1 parts compost
- 3 parts coconut coir
- 1 parts perlite
Potting On Mix (Ideal for baskets, tubs and containers)
These plants, often found in baskets, tubs and boxes require more nutrients than seeds and cuttings but still prefer a well-drained, airy potting compost:
- 2 parts compost
- 1 part manure or worm castings
- 2 parts coconut coir
- 1 parts perlite
- small amount of slow-release fertiliser pellets
Potting Compost For Established Permanent Plants
Established plants that you intend to keep in your pots for more than one year require more nutrients and less aeration and inert content. Heavy mixtures also mean the pot is less likely to blow over in the wind. We suggest compost and manure mixed with only a little perlite and coconut coir. Add slow-release fertiliser once or twice a year:
- 2 parts compost
- 2 parts manure or worm castings
- 1 part perlite
- 1 part grit/course sand
- small amount of slow-release fertiliser pellets
We’ve used mixes like this for years with great results.
Can you save money and just use regular multi-purpose compost? Sure, but for seeds and cuttings, your success rate will be lower. Also, any over or underwatering can cause problems that you would otherwise get away with had you used a more airy, well-draining mix.
Feel free to adjust the mixes, these are just the three that we’ve found work the best.
Is creating your own potting compost worth the effort? Why not just buy a bag of potting compost from a garden centre?
If you’re only growing a handful of plants then a bag or two of potting compost from the local garden centre would be cheaper and easier. For those of you wanting to grow lots of plants, making your own is timesaving, cost-effective and also educational.
Don’t forget; it’s far cheaper to grow from seeds and cuttings than buying pre-grown established plants from garden centres.
Check out the products below that we often use when potting seeds, cuttings and plugs:
These lightweight secateurs are razor-sharp so are ideal for woody stems as well as softwood. They have a comfy ergonomic handle and are geared for ease of use. The geared system increases the cutting power.
Light, airy, free-draining and cheap; coconut coir is the perfect growing medium for seeds, cuttings and small plugs. Add in compost or manure for nutrients and you’ve got yourself the perfect potting compost.
Propagation kits contain a tray with separate cell inserts and a lid to increase the humidity. Cheap and easy to use, these kits make propagation easy. Replace the lid with a plastic bag if you need more vertical space.
Incredibly lightweight, this unusual material aids aeration, soaks up excess moisture preventing overwatering & also releases moisture during dry spells, perfect for seed & cutting potting composts.
A warm moist environment helps seeds and cuttings to grow quicker and with an improved success rate. Use a heated propagator any time of the year and you’ll be growing new plants in days, not weeks.
Use wooden, degradable markers to label your seeds or cuttings with the date & also the name of the plant species. They’re especially useful if you intend to grow a lot of seeds/cuttings in pots or trays.
EXPLORE MORE OF OUR CONTENT BELOW:
“Our Plants” Section
The “Our Plants” corner of our site contains everything you need to know about the plants the DIY Gardening team is currently growing in our gardens. Start here
Soil and Compost Guides
Discover how you can easily make your own compost mixtures from home. From potting mixes and ericaceous compost to everyday garden feed. Start here