One of the big differences between now and the time before gardeners relied so much on peat-based composts is the rise in container growing. An army of modern amateur gardeners has to put up with small gardens, and possibly with no soil at all. Growing plants in containers allows us to garden wherever we like, and even to grow plants that would not thrive in our soil. Some plants are grown in containers to keep them under control; others so that they can be moved indoors in winter to ensure their survival.
All of these containers have to be filled with something, and the two off-the-shelf choices are multipurpose compost and soil-based growing mediums (the John Innes mixes here in the UK are standardized soil-based mixes, not a brand name). Both of these will contain peat (and almost certainly a lot of it) unless they specifically say they are peat-free.
The same is true for grow bags – unless they say they are peat-free then they will contain a lot of peat. Grow bags are mostly used to grow food, very often for fruiting crops like tomatoes and cucumbers, and a popular choice for British gardeners.
The good news is that peat-free multipurpose compost is increasingly easy to find, and improving in quality. Companies are also now supplying it in grow bags for those of us who want to use them. (As far as I am aware, VitalEarth are the only UK company currently supplying peat-free versions of the John Innes soil-based mixes.)
For mature plants, the consistency of the compost is far less important and you shouldn’t need to sieve it – plants can cope with larger particles. Multipurpose compost and loam-bases mixes generally contain enough nutrients for your plants for about six weeks, after which you should be thinking about supplementary feeding (certainly for vegetables and fruits – some flowers are better left in a low nutrient environment to encourage flowers rather than leafy growth).
With plants in containers needing constant watering and feeding anyway, the only problems I can foresee for gardeners who are moving from peat-based to peat-free mixes is that the watering frequency may be slightly different (as the mixes will retain water differently) and composts that have been bagged before they were stable (a common complaint with cheaper, poorer quality peat-free mixes) may require extra nitrogen feeds earlier on to compensate for continued decomposition locking up nitrogen.
DIY potting mixes
It’s easier to make your own potting mixes than it is a seed or seedling compost, as there is less need for it to be sterile or to have a very fine texture. The key to making your own potting mixes is to make as much of your own garden compost as you can – set up a compost bin to rot down garden waste. If you’re short on space then consider a wormery (worm composter), which deals almost exclusively with kitchen waste to produce a rich compost and plenty of run-off that can be used as a liquid feed.
Leaf mould, grit or sand, loam (an ideal top soil) and coir or rice hulls are all useful ingredients – I’ll be talking more about each one later in the book.
If we go back to Monty Don‘s article in the Telegraph, his recommended container mix is 33% garden compost, 25% loam, 25% leaf mould and 20% grit. I think his maths is a bit wonky, but it’s more of a guideline than an exact recipe! He’s also well-known for using mole hills as his source of loam.
Allan Shepherd recommends using a mixture of leaf mould and comfrey leaves, which is left for several months for the comfrey leaves to rot away to virtually nothing – they add nutrients to the mix which are absent in pure leaf mould.
In their I Don’t Dig Peat campaign leaflet Garden Organic offer several potting mixes One is a simple mix of 3 parts leaf mould to 1 part worm compost; another a loam and leaf mould mix with added commercial fertilizers – seaweed meal, bonemeal and hoof and horn – for the nutrients. If you want or need to add commercial fertilizers to your mixes then you have plenty of choices: synthetic, organic and even vegan fertilizers are readily available mail order even if your local garden centre or nursery doesn’t stock them.
As before, you will need to tailor your home-made potting mixes to the ingredients you have available or can purchase. You also need to think about which plants are going to be planted up in it, and how long they’re going to be in their container. Perennial plants that are going to be in their pot for some years appreciate a soil-based mixture that is better at holding nutrients and water in the long-term and less prone to slump – composts with a high degree of organic matter decrease in volume over a year and the plant gets lower in its container. That’s not an issue for short-lived plants or those that are regularly repotted, but it’s not ideal for a long-term planting.
Short-term crops are perfectly happy in a potting mix that doesn’t contain any soil and a soil-free mixture is much lighter – weight is very much an issue if you’re using your containers on roof-tops or balconies, or if you intend to move your containers around a lot.
And, of course, the nature of your container itself is something you should take into account.