Choose from peat or peat-free composts, with different types explained and useful buying tips
'The pro-peat brigade points to peat's track record of consistency and ease of handling. The anti-peat lobby points to the harm done to sensitive wildlife areas when peat is harvested'
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| Sue Hamilton uses peat-free composts
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For most gardeners, a multi-purpose compost that you can use for seed sowing, rooting cuttings and potting up containers and baskets is the easiest and most economical choice. It's then a matter of working out how much you need and where to get it from.
Peat dilemmas
Gardeners and horticulturalists have strong feelings about the role of peat in compost mixes. The pro-peat brigade points to peat's track record of consistency and ease of handling. The anti-peat lobby point to the harm done to sensitive wildlife areas when peat is harvested, plus the need for us to recycle more of our own green waste rather than dump it in landfill.
Gardening Which? has independently and impartially trialled compost for over 20 years. Latest results show that 'New Horizon' peat-free multi-purpose has consistently done well over six years for young plants and container growing. It fares less well for sowing seed, so they recommend a peat-based compost for starting off seeds. Their trials also show that a good multi-purpose can suit seeds, so there is no need for a seed and cutting compost.
John Innes
Composts devised at the John Innes Institute in the 1940s are known as John Innes composts. At the time, they were an advance on the traditional recipes as they were more precise in the fertiliser they added (No1, 2, or 3 refers to the amount of fertiliser added - the higher the number, the more fertiliser). They also required the soil to be sterilised and used peat (which was effectively sterile) instead of manure.
There are many brands of John Innes and quality varies due to the source of loam and grade of the sand, and due to the weight of these components their distribution is patchy. The loam adds a reserve of nutrients and a structure that lasts longer than peat, as well as some weight. These composts are useful for long-term planting, such as trees in containers, or for top-heavy plantings, such as standards. The weight makes buying compost and moving containers heavy work so for annual plants there's little advantage.
The John Innes Institute has just updated the formula, dispensing with the loam, peat and synthetic chemicals that have been replaced by recycled green waste. Called Genie No1, 2 and 3, they are available for the first time this year; contact Vital Earth on 0845 054 4949.
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| A multi-purpose compost is fine for pots
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Right choice for pots
For planting-up hanging baskets and containers on patios, you can use a multi-purpose compost, perhaps adding some water-retaining gel and some slow-release fertiliser when you plant up to help keep the moisture in and to provide nutrients all through the season. Most composts only contain enough fertiliser to keep plants growing for around six weeks, after that you should apply extra feed. There are also composts especially for containers - these usually have water-retaining gel already in them or you can use a John Innes No2 or 3.
Ericaceous mix
In a normal peat-based compost, lime is added to bring the mix to neutral pH (peat is naturally acidic), so a wide range of plants can be grown in it. Simply by leaving the lime out, a peat-based compost can be described as 'ericaceous' and will be ideal for acid-loving plants such as camellias and rhododendrons. Unfortunately, it is far harder to produce a peat-free ericaceous. Research is being done with composted pine needles and bracken, but at present you are unlikely to find one easily. You're best option is to look for a peat-reduced ericaceous.
Growing bags
At one time this was the cheapest way to buy peat-based compost, but they are often heavily discounted so the cheapest grade peat was used, and their thin shape made watering a nightmare. Now there's a choice of peat-free growing bags and there are also new designs with more root depth, often known as planters. This April, Humax extended its range to include 10 organic bags with specific formulas for different vegetable crops.
Buying tips
Estimate how much compost you'll need for the rest of the season, typically there will be a '3 for the price of 2' offer on larger bags. There's no harm in a bargain but make sure you'll use it this season. Look for fresh stock; bagged compost left outside for long periods can get waterlogged. This can lead to deterioration in the fertiliser and make it smelly and unpleasant. It would be great if compost bags had 'sell by' dates clearly stamped on them - until that happens, buy from somewhere with a high turnover, and feel the weight of each bag - reject any that appear saturated with water.
denotes Subscriber-only content | Wednesday 23 July 2008 | Help | Glossary 
