Peat Free Trials

Introduction

As a carnivorous plants nursery, whose plants traditionally are grown in a mixture of peat with something else (perlite in our case), it has become increasingly important to be able to provide peat free alternatives. Not because of customers’ demand, but because the ban will come (good political sound bite) at some point, and we need to be ready. We have been trialling a variety of different mixes for about 7 years. Sarracenias are fairly easy, they grow in most things, as long as the medium is nutrient free. Some of our display plants have been in the same pot in coir chunks for many years, and are absolutely fine. The original Sarracenia peat free mix (Melcourt growbark, perlite and granite) worked ok, but root growth when repotting after a few years is clearly reduced. Results are better when using fine grit, but still not the same as in any other medium we have trialled.

Figure 1 Sarracenia in Rockwool mix after 1 month

After reading the article in the Guardian about the successful RHS trial with the headline “carnivorous plants grow better in peat free”, we decided to do our own unbiased trial. We took into account the issues we had with the RHS trial: Only Sarracenia were used, the comparison medium was pure peat, one of the trial mediums (Thrive) had undisclosed components.

Methodology

We have used a variety of composts for these trials, more details below. The one we have not trialled this time is the coir chunks. Established Sarracenia seem to be doing well in anything. However, we lost 1/3 of the Sarracenia that we split and potted in coir chunks in an earlier trial in May/June. Dionaea Muscipula (VFT) did not like it at all, and all died. Drosera results were the same. Cephalotus and Nepenthes seem to do well in coir chunks. That, and coir’s greater demand for water, have made us exclude coir chunks as an option for this trial of Sarracenia, Dionaea Muscipula (VFT) and Drosera.

We previously (end of July 2023) potted up several Sarracenia in a Rockwool mix. They have done really well in this first month, with great colour, so we decided to make 2 different rockwool mixes part of the trial. See pic on the right.

The main part of the trial are tissue culture Sarracenia plugs and seed grown VFT plugs we bought from the Netherlands from a well established company with high quality plants. 

Figure 2 Sarracenia plugs
Figure 3 Dionaea muscipula plugs

They looked very similar, so we simply started at one end of the tray, without selecting specific plants. We did not remove all of the peat that the plugs were in, mainly because many previous trials have shown that if the plants do not like the mix they will show that soon enough, regardless of whether their initial start is in peat. We included a few Drosera, as well as some Sarracenia that had to be split (Sarracenia cv Eva) and a slow growing tissue culture leucophylla hybrid from Italy, Sarracenia x Bielsa (aka)

Compost Mixes

Peat/perlite 50/50 – white sticks in the pot
Without wanting to disprove findings from a trial the RHS has carried out with Sarracenia in peat free mixes, we would have to add the caveat that these were compared with plants potted in pure peat. We do not actually know anybody who grows their plants in pure peat, so we have used a standard peat/perlite 50/50 mix for comparison.

Figure 4 Peat/perlite mix

Sphagnum/perlite 50/50 – orange sticks with SP
This mix speaks for itself. We have to guillotine the sphagnum to make it suitable

Figure 5 Standard (wholesale)
sphagnum/perlite mix

The Sphagnum Shop Argentinian sterilised Sphagnum/perlite 50/50 – yellow sticks with ASP
This mix speaks for itself. We have to wet and guillotine the sphagnum to make it suitable

Figure 6 Argentinian sphagnum/perlite mix

Pine bark (growbark) based peat free (traditional mix) – Purple stick – either PF or PF VFT
This pine bark based mix requires different mixes for different plants
For Sarracenia we use 2 bark, 1 perlite, handful Cornish horticultural grit
For VFT we use 3 bark, 1 perlite

Figure 7 Pine bark/perlite

Rockwool mix 1 – Green stick with RP
This mix has 1 unit cut Rockwool, 1 unit cut sphagnum (SP), 1 unit growbark, 1 unit perlite

Figure 8 Rockwool/standard sphagnum/
growbark/perlite mix

Rockwool mix 2 – Blue stick with R
This mix has 1 unit cut Rockwool, 1 unit cut sphagnum (SP), 1 unit growbark.

Figure 9 and 10 Rockwool/sphagnum
(SP)/growbark mix

Rockwool only – Red stick with R only
Speaks for itself

Thrive – Pink stick with T
This mix was also used in the RHS trials (Sarracenia only), seems to contain very fine perlite, pine bark and coir, at a guess

Figure 11 Thrive mix emptied from bag Figure 12 Adding water to thrive (as per instructions)
Figure 13 Thrive mix ready for use

Costings

After measuring them all, it turns out that all the mixes used cover more or less the same amount of pots. As the only mix we bought ready mixed came in a 5 litre bag, we have calculated everything with these 5 litres in mind (approx. 20 x 8.5cm pots)

For any mixes with rockwool we have given 2 different figures for cost. From this year, the RHS have banned the use of oasis for flower arranging at shows, forcing those exhibitors to use a certain type of rockwool, which for flower arranging purposes can only be used once. No chemicals/nutrients have been used while the flowers are displayed, just water, so we have been collecting this free of charge. Not only excellent recycling, as rockwool does not break down, but also a big cost saving. The calculations do not include the time we would have to pay for somebody to cut it into small pieces. To purchase the rockwool (already pre-milled medium size) in bags is costly, but time saving.

Sphagnum moss is very much the same. Expensive to buy pre-milled (only found it in the US), in our costings the time for somebody to guillotine it medium has not been included.

Calculations for mixes all based on 5 litres, calculations done in 2023, based on 2023 prices (Excl VAT)

Peat/perlite 50/50 £0.80

Sphagnum/perlite 50/50 £1.42

Argentinian sterilised Sphagnum/perlite 50/50 £2.82

Pine bark based peat free (traditional mix) £0.90

Rockwool mix 1   £0.88   £1.92

Rockwool mix 2  £0.75  £2.16

Rockwool only £ 0.00 £ 4.14

Thrive  £6.99 retail

Results

The trial has run from August 2023 to August 2024. All plants were grown in a polytunnel (unheated), VFT fleeced if below -5°C, all stood in trays with rainwater in summer, and checked for weight/dampness in winter.

Not sure if the pictures do it justice, but the results are very clear if you see the plants in situ. I have taken a video as well, which I can send via What’s app if anybody is interested

Overall best results are for all three genuses (Sarracenia, Dionaea and Drosera) grown in peat/perlite (PP on pictures below) or the The Sphagnum Shop Argentinian sterilised sphagnum (ASP). The worst results were pine bark (growbark – PF or PF VFT) and Thrive (T). Rockwool, in any mix, with or without perlite, even on it’s own, has done ok. Nothing to write home about, but all plants are alive. Because firstly, once we run out of freely collected rockwool, it is quite expensive, and secondly on moral grounds, as the rockwool will never decompose, we have decided to discount this as an alternative.

Drosera

  • This was only ever a tiny sub-trial, with not a lot of data, sample too small, and compared against our standard Drosera on the nursery in peat/perlite mix
  • Only had enough Thrive left to try one, which is alive but sparse
  • Rockwool did ok, even root cuttings came up
  • Peat/perlite and The Sphagnum shop Argentinian sphagnum look the best
  • New trial, which we are starting in September, will include more Drosera

 

Dionaea muscipula (VFT)

  • Both pine bark (PF VFT) and Thrive (T) were poor. We lost 1 out of 3 in pine bark, and none of the ones in Thrive look great
  • Rockwool has done well, most plants are alive and growing well
  • The standard sphagnum (SP) has overtaken the VFT’s so they are not brilliant
  • As with Drosera, peat/perlite and The Sphagnum shop Argentinian sphagnum (ASP) have done the best, with good colouring, new growth and healthy looking plants

 

Sarracenia

  • The differences are not as big as with the VFT’s
  • Pine bark (PF) and Thrive (T) are clearly the smallest and with less colour. Again, lost 1 out of 3 in the bark
  • Rockwool has done ok, plants are growing, smaller
  • Standard wholesale sphagnum (SP) did ok with the plug plants. However, on the plants that we split (Sarracenia cv Eva) it has overtaken the plants
  • The Sphagnum shop Argentinian sphagnum (ASP) as well as the peat/perlite mix stand out with new growth, height and colour

Conclusion

The best result, including value for money is the 50/50 peat/perlite mix. The Sphagnum shop Argentinian sphagnum has done just as well. However in cost (£0.40 more expensive per litre) and carbon footprint (it comes from Argentina) it falls behind. On top of that it still has to be milled, as does our UK wholesale sphagnum, which is time consuming (not calculated). However, at this moment in time, we would say that this is the most credible alternative to peat.

As the peat ban may be postponed, but will arrive at some point, we have decided to do a 2nd trial, using The Sphagnum shop Argentinian sterilised sphagnum. We have managed to source an alternative sterilised sphagnum, from Europe, sustainable, still in the development stage. We will trial seeds, seedlings, young plants and more mature plants in the search for an almost multipurpose replacement for peat! Will keep you posted