The case for peat-free compost

Saturday 23 February 2013

The best way to get your plants off to a good start is with the right seed sowing compost.

Custom byline text:

Dave Allan

Traditionally, peat has been widely used in commercial composts even though it's long been recognised that extracting it not only destroys biodiversity but also releases huge quantities of carbon, and therefore CO2, into the atmosphere.

Despite this, 70 million cubic feet of peat is used by gardeners in the UK each year, the reason being that peat has a fine texture and retains moisture beautifully, so it's an ideal bulking agent in composts. Not only that, but recent trials by Which? Gardening showed peat-based compost was a much more effective growing medium than peat-free alternatives.Which? assessed how well 27 composts worked with seedlings and young plug plants and found J Arthur Bowers seed and cutting compost, which is 95% peat, scored 91%. Verve Grow Your Own growing bag scored 91%, with 55% peat content. By contrast, the highest scoring peat-free medium was Miracle Grow Expand N.Grow with 73%, and the best organic mix was New Horizons at 60%.Despite these results, gardeners should ask themselves if they're prepared to contribute to major environmental damage for the sake of a few seedlings. Also, with peat set to be banned from garden composts in 2020, it's time for all gardeners to think about alternatives.The amount of nutrients plants require varies as they grow, and manufacturers can add these, but the structure of the compost is almost equally important. Tiny seeds need a fine texture and peat-based composts easily provide that. At the pricking-out stage they require more open material, and this is even more important in containers. Again, peat provides the answer for all of this.It's much harder for peat-free composts to meet these requirements. This explains why they are nearly always sold as "multi-purpose", even though they're not as "multi" as we'd like. When preparing this compost, manufacturers use green waste, forest bark, wood waste or coir in different proportions.Green waste – mostly municipal compost – is often very dense; woody waste is too open and has lots of wee bits of bark mixed in; and coir, a by-product of the coconut industry, is fine and often dusty. Manufacturers have to find a good balance of these ingredients and it's not easy to come up with the right formulation.In trials at its garden at Wisley, the Royal Horticultural Society (RHS) experimented with various ingredients, removing woody material and adding vermiculite – a mica-like mineral which is mined around the world – to improve drainage. The RHS grew begonias and lettuce seedlings in different mixes. Because coir is fine, they simply added one part vermiculite to eight parts composted coir. Wood fibre had too many large particles, so they used a 6mm sieve to remove the larger particles and mixed one part vermiculite to four parts woody compost. Green waste is, by and large, finer than woody material but still retains some larger bits, so the RHS sieved this too then used a mix of one part vermiculite to four parts green waste.It would be impossible for gardeners to make their own compost mixes like this and achieve the right level of nutrients. The solution would be to modify compost such as New Horizons for use at the seed-sowing stage. Use a fine sieve to remove the larger woody particles and add vermiculite to provide drainage while also retaining nutrients. Multi-purpose peat-free composts should work for larger seedlings and in containers.Although this means more work it's far better than supporting environmentally damaging peat extraction. Hopefully, better peat-free products will soon become available.Visit askorganic.co.uk. Email your gardening queries to da@askorganic.co.uk

Contextual targeting label:

Environment

Commenting & Moderation

We moderate all comments on HeraldScotland on either a pre-moderated or post-moderated basis. If you're a relatively new user then your comments will be reviewed before publication and if we know you well then your comments will be subject to moderation only if other users or the moderators believe you've broken the rules, which are available here.

Moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours. Please be patient if your posts are not approved instantly.

The case for peat-free compost

Commenting & Moderation

MOST READ

SPONSORED LINKS

MOST COMMENTED