The hidden star is the compost. In this case two thirds New Horizon peat free compost and one third home made worm compost. Photograph: Mark Ridsdill Smith
Browsing through the thousands of gardening images on Pinterest or Facebook, you’ll be hard pressed to find one of compost. Perhaps this isn’t surprising – compost isn’t photogenic or sexy.
But the low profile kept by compost is misleading. Because behind every image of a beautiful and abundant container of edible plants, the compost (or growing mix) is the key to the success. Like the composer of a successful song, it often remains invisible, but the song couldn’t even begin without it.
So compost is actually the star of the show, albeit a shy one that keeps out of the limelight.
It’s also one of the hardest things in gardening to learn, teach and write about.
That’s partly because there are infinite variables to compost and growing mixes. And without doing scientific tests, it’s hard to be sure what really makes a difference. Some gardeners will swear by adding biochar, others will tell you that the secret is to add rock dust or mychorrhizal fungi – while others will tell you that you need all three – or something else entirely.
It’s also tricky to recommend any particular brand of commercial compost. Which? do trials each year. These are interesting and useful but are always one year out of date (the trials have to take place the year before the results are published) – and composts are fickle things that can change each year (and even between batches). Unfortunately, this fickleness is particularly true of peat free composts – the only option if you want to grow sustainably, in my opinion.
So compost and growing mixes are complex, but here are four things you can do to help you learn about compost and avoid growing all of your crops in a bad batch of compost, which will definitely be demoralising – and may make you give up growing forever!
1. Start off with the best peat free multipurpose compost you can get
Very cheap composts are often a false economy. Of the peat free brands that are widely available good ones include New Horizon and Vital Earth. B&Q peat free can be lumpy but is often alright (sieve it before sowing seeds in it). Less widely available, but also good, are Fertile Fibre and Moorland Gold.
2. Try more than one brand of compost
This way you’re not putting all your eggs in one basket. And you’ll also learn by seeing, feeling and using different mixes. Remember to label which container you put which compost in, otherwise, like me and 95% of other growers I know, you’ll think you’ll remember but then forget.
3. Try some green waste compost
More and more councils are offering green waste compost for sale, often at low cost. This varies in quality but often it’s excellent. Check your local supply has been certified to “PAS 100” (this tells you it’s been checked for weed seeds and heavy metals). I know a number of people who grow in it exclusively – and very successfully too. You can often use it neat in pots (though not for seed sowing) or you can mix it with other compost – experimentation, as with all this, is the key.
4. Get a wormery
Worm compost is the most wonderful addition to any growing mix. It adds lots of nutrients but most importantly it’s teeming with soil life. Not just worms (which will do a useful job in your pots) but also bacteria and fungi that play an essential role in creating a healthy soil. Bought compost is usually low in soil life – so adding it can make a huge difference. We’ll look at wormeries – and other fertilisers – in more detail in the future.
Ultimately experimenting, learning and finding what works for you will make more difference to your growing success than anything else.
For the more adventurous, there is an array of ways you can try to improve and sustain the life of commercial composts. Adding something to improve the structure, for example. However this is not essential: if you start with a good quality growing mix, most crops will grow well in that. But, if you like the idea of experimenting, here are some ideas you can try:
• If you find some nettles, comfrey, seaweed (rinse first) or grass clippings you can add 1/2 – 1 inch on top of the compost as a mulch round your plants. As they rot down, nutrients will be released into the soil.
• Many city farms will give you manure. Make sure it’s well rotted and bring home a bag to try. Put a few inches at the bottom of bigger pots when you replant them, or add an inch or two around your hungry crops (tomatoes, and courgettes, particularly) when they start to flower and fruit.
• In deeper pots (12 inches or more) add a layer of twigs or cardboard mixed half and half with green food waste (such as veg peelings) in the bottom inch or two of the pot. This will slowly rot down to create compost and provide a source of food to sustain soil life in your containers.
• Try adding 10 – 20% rock dust (now sold by B&Q) or biochar (finely ground charcoal) to your pots. Rock dust will add a long term supply of minerals and trace elements. Biochar helps retain water, improves drainage, and provides a home for soil life in its millions of tiny pores.
Next time we’ll look at some of the most fun and productive crops to grow in containers. Until then, have fun getting your hands dirty!