Sustainable growing media – the future  

There are a host of reasons UK and Irish growers are adopting sustainable growing media ranging from environmental, legislative and consumer pressures – to those that simply prefer it to peat.  

While many are embracing the move to peat-free growing media, some are naturally more resistant to change. We often hear growers say they’ve used peat for decades and believe it’s the best, or that they believe peat free media does not perform as well, impacting on plant quality, while some believe peat-free alternatives are less environmentally friendly than peat.  

There is no denying the move to sustainable growing media has thrown up potential challenges, many of which are being addressed with new technologies.  But first, let’s see if peat is the perfect growing medium.   

Rose-tinted spectacles

Developed by GCRI back in the late 1960’s, peat based growing media is ‘clean’, reliable, inert, has a low pH, is low in available nutrients, offers good nutrient buffering, has excellent water holding capacity, and is economical.  However, that said, it is perhaps time to remove the rose-tinted spectacles.  Firstly, there are lots of different peat types, with very different characteristics.  

Sedge peat aside, the original old black peats have excellent buffering capacity and hold water well.  Fisons Horticulture (now ICL) utilised older peats to make its highly successful Levington M3. Due to its high buffering capacity, 2 to 3 times more fertiliser could be added (compared to competitors using other peats), to create a consistent high quality bedding mix, feeding plants for 8 to 10 weeks. 

However, older peats are quite fine with a low air-filled porosity (AFP), so can sit wet and cold in poor weather conditions. They proved challenging for outdoor CNS crops – due to water-logging, moss and liverwort growth – and were also not well suited to pot plants, such as Poinsettias and Cyclamen.  Maybe they were not quite so perfect? 

At the other end of the scale, Baltic peats are significantly lighter with a higher AFP. In some ways these provided the answer. However, with no buffering properties and poor water holding, nutrient management and wetting up could be challenging. If pots dried out it could spell disaster and, if plants ran out of feed, it was very difficult to bring them round – while shrinkage and slumping in pots was also a potential problem.    

So, Levington opted for something in the middle; mainly Irish peats mixed with some slightly younger UK peat, preferably harvested from the middle layers of the peat bog.  Our team developed ways to screen and blend the different peats to optimise AFP, water holding and buffering capacities.  This presented options to blend a range of Irish, Scottish, and Baltic peats to optimise the benefits of each component. It opened the door to the development of bespoke mixes, tailored to specific crop types and growing situations. 

Ideal growing media?

So, was peat the perfect growing media? In some respects – yes, however, if it rained a lot and we couldn’t harvest what was needed, non-peat materials (which at the time were unpopular) had to be added to eek it out.   

The peat we did have tended to be wet and heavy, which meant the structure could potentially break down making it too fine.  As peat supply was often short, piles could get low creating potential for weed contamination and then peat suddenly became more expensive.  

To an extent, we accepted the shortfalls and adapted, learning how to use peat to its best potential – but it took time.  Paul Waller, Fisons’ then technical manager, designed the original Levington growing media range and once told me; “It’s taken us 30 years to get peat right and we’re still working on it.”  To be fair, that was 20+ years ago! But what he said reflects the fact that nothing is perfect from the start. 

Rise of genuine alternatives

As an industry, we’ve been experimenting with peat free growing media for over two decades. However, it’s only in the last five years or so that we’ve got serious about it.    

Today, it isn’t about peat – it’s future is limited at best. But, after years of significant investment, in both time and money, there are genuine alternatives.  Raw materials that perform in mixes in a very similar manner to peat.  Indeed, new sustainable mixes can offer some advantages over peat – as well as raising issues that need to be managed.   

At ICL we have researched and developed a range of new technologies to help growers succeed.  

So, while peat – at its best – is an ideal component for growing media, it still has drawbacks.  Sustainable raw materials are just the same, they offer some genuine benefits and, in turn, come with challenges to overcome.  We must all learn to adapt the products and our management processes to maximise their potential. 

Keeping up to date

Over the coming year, Technical Matters will continue to bring you updates on new ICL products specifically developed to optimise the performance of sustainable growing media, insights from our high-experienced technical team along with visits to UK growers embracing these new sustainable media.  

In July, we will be running our popular Hort Science Live (HSL) event over two days at the National Institute of Agricultural Botany (NIAB) at Cambridge.   

HSL 2024 will provide an opportunity to see at first-hand the result of our latest peat-free trials, find out more about our expanding range of peat-free alternative raw materials, and to learn more about our innovative nutritional and water management technologies to help growers confidently transition to peat-free growing.