Produce > Under Glass
Potting Compost
Tee Gee:
I think most of us on the forum are aware that suppliers of potting composts will not be allowed to add 'Peat' to the mix. At least this is the case for the compost sold to the general public, it is still unclear if this ruling will apply to commercial growers.
As has been reported over the past few years on various gardening related forums, some of the potting composts being sold as 'peat reduced ‘or 'peat free' have left a lot to be desired. Add to that, this year (2023) has seen massive rises in the cost of purchasing such composts.
For example, when these products first appeared on the market, they retailed at around 6p-7p per litre now it is around 10p-11p a litre a rise of around 50%-60% for which in many cases is still for rubbish!
To this end, particularly since giving up my allotments I have started to use containers to grow quite a lot of my stuff, and I am finding that it is becoming quite an expensive hobby!
To try and subsidise these costs, I have been experimenting for the last couple of years making my own potting composts!
The idea came to me when I looked back on my 50+ gardening years and found that I used the same soil every year and basically all I did to it was added humus (farmyard manure) and fertiliser to rejuvenate the soil, so I thought I would try the same with my spent compost!
OK as I was soon to find out, there was a bit of a learning curve for example, establishing a recipe on how to add the correct amount of humus and fertilisers to the spent compost, so I plumped for the John Innes method which is;
7 parts Loam
3 parts Peat
2 parts Coarse sand or Grit
To these I was required to add
2 parts, hoof and horn. (N)
2 parts superphosphate. (P)
1 part sulphate of potash. (K)
1 part ground limestone to control the pH**
To simplify this one can now purchase pre-formulated 'all in one' mixes which takes away the need to purchase Hoof & Horn, Superphosphate and Sulphate of Potash separately.
This was the point where I chose to differ slightly from the manner on how commercial mixes were made up.
I substituted Spent Compost for the Loam content, well-rotted Horse Manure for the Peat content and Perlite for the Sand/Grit. (I find sand makes the finished product too gritty!)
** In terms of establishing the pH I prefer to test the Loam, Manure and sand/grit after mixing then adjust the mixture with limestone as required.
I found with this recipe that the initial pH can be quite variable once the ingredients have been mixed together.
This is the area I had a problem with because I did not know how to calculate how much hydrated lime / limestone to add to my base mix to obtain a pH of somewhere around 6.0 to 7.5 and because of this I just used the 'Trial & Error' method.
For example, I have an analogue pH Tester where the probe gives me some guidance, although I am convinced it is reading around 1pH unit too high based on tests I have made with non-bleed pH indicator strips.
I am pleased to say my results are getting somewhat more consistent.
How I did this initially was to work with a 10litre bucket of 'Base Mix' which I tested with the pH tester and a pH indicator strip and recorded the pH result.
Next, I mixed in two 15ml spoonsful of lime to the 10 litres of 'Base Mix’ and tested it again with the pH tester and a pH strip and recorded the reading.
I carried out several tests in this manner where I added varying amounts of lime subject to the +/-pH readings I recorded from each batch.
Eventually I found a correlation in the results to show approximately how much lime I had to add to get to my target of 6.5.
To simplify this even more, I started making 40litre batches to reduce the number of tests I had to make.
I purposely do not add fertiliser at this stage as I prefer adding this when required, i.e., when I find I need a compost mix that is the equivalent of either Ji 1, 2, or 3 compost.
All I do is add the required amount of base fertiliser to a given quantity of my "Base Mix" and I have the desired compost I want.
In terms of cost, Ji 1 is costing me around = 3p/litre – Ji2= 3½p/litre – ji 4p/litre.
Hope I have not bored you all too much, but as I was making some notes for my records (my memory is not as good as it once was)I thought I would let you know what I am getting up to, now that I don't have an allotment
Tee Gee:
Tried yesterday to add a few images, but they were too large, maybe his time
woodypecks:
Enjoyed reading your thoughts and experiments on potting compost Tee Gee . It is becoming expensive .... not only that but it is so darned heavy to move about too ! :coffee2: Debbie :wave:
Tulipa:
And it's good to be re-using the compost, I am definitely keen to start something off this year, thanks for all your info Tee Gee :icon_sunny:
Beersmith:
An interesting contribution.
Would you be able to say a little more about the physical properties, like drainage, water retention, aeration and similar for your formula? These are the aspects of the modern peat free composts that are usually so much worse than the peat containing types.
Navigation
[0] Message Index
[#] Next page
Go to full version