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Allotment Stuff => The Basics => Topic started by: Spudbash on February 22, 2010, 15:53:10

Title: Making your own potting compost
Post by: Spudbash on February 22, 2010, 15:53:10
Hi all,

I'm finding Allotments 4 All brilliant for everything from rat management to fruit tree bargains, so a big thank-you to everyone who's posted helpful advice for the benefit of the rest of us.  ;D

I've just ordered a Scheppach hand rotary soil sifter so that I can make my own potting compost. I want to use the potting compost to grow tomatoes, cucumbers, melons and also various fruit trees (yes, I got carried away shopping!).

My garden soil is quite good - a sort of stony woodland loam, I suppose, and I've got leafmould from the two huge oak trees in the garden. I also have compost (from lawn clippings, herbaceous stuff and fruit and veg waste), and a big sack of lime; also some ancient bags of chicken manure pellets, seaweed meal and sharp sand. So I think I've got plenty of suitable ingredients.

All I need now is a recipe or two to suit what I want to grow. Any tried-and-trusted ideas out there, or any links to websites with suitable info?

I'll be really grateful...  ;D
Title: Re: Making your own potting compost
Post by: chriscross1966 on February 22, 2010, 17:16:24
No chicken poo in the seed compost :D
Title: Re: Making your own potting compost
Post by: Spudbash on February 23, 2010, 10:52:20
Thanks crisscross!  ;D I should have said that I will carry on buying seed compost for sowing - not just to avoid chicken poo scorching the seedlings, but also to prevent damping off.

What I want to do is to avoid having to buy huge amounts of compost for fruit trees and veg in pots, in future. (My space is limited because there are no allotments where I live, so I'm cramming as much as I can into my garden.)

If anyone out there has any more advice, I'd love to receive it.
Title: Re: Making your own potting compost
Post by: Robert_Brenchley on February 23, 2010, 10:57:32
I used to follow the standard JI recipes (they must be out there on the net somewhere; does anyone know where?), but I substituted leafmould for peat. I'm seriously thinking of going back to rolling my own.
Title: Re: Making your own potting compost
Post by: Baccy Man on February 23, 2010, 11:07:34
The John Innes recipes amongst others are available here:
http://www.the-organic-gardener.com/making-compost.html#recomendrecipes
Title: Re: Making your own potting compost
Post by: Ian Pearson on February 23, 2010, 11:09:33
Just something to watch out for... some leaves are allelopathic (release chemicals that inhibit growth or germination). What I don't know is how long the chemicals persist. Leaf mould takes about 2 years to really form, so maybe that's long enough for them to break down, and be safe to use in seed compost

I don't know, but it might be worth trawling the internet to check.
Title: Re: Making your own potting compost
Post by: Robert_Brenchley on February 23, 2010, 11:24:12
Use deciduous leaves, which break down rapidly, and don't produce much humic acid. Pine needles rot much more slowly, and produce a much more acid soil due to the humic acid they release. They might be OK as an additive for acid-loving plants.
Title: Re: Making your own potting compost
Post by: Spudbash on February 23, 2010, 13:07:02
Thanks guys - and it does seem to be a guy thing, doesn't it?!

I think my oak leafmould will be ok, particularly as I have lots of really old, crumbly stuff.

I'll take the link, thanks, Baccy Man - couldn't find anything online when I looked, but there do seem to be mud-pie recipes a-plenty, here. And at the end of the day, it's all about mud pies, isn't it?

 ;D ;D ;D


Title: Re: Making your own potting compost
Post by: Ian Pearson on February 24, 2010, 20:00:50
I do buy some compost, but I recycle it as much as possible.
At this time of year I'm just about due to make up my mix for the busy spring period. The main ingredient is all last year's spent seed compost, and compost from any old pots, and spent compost from a neighbours window boxes, which has all been stored overwinter in a bin. I start by removing any roots and crocks, then add about half as much new compost, a couple of shovelfuls of garden soil, maybe some builders sand if any can be 'aquired', and finally a handful of organic fertiliser, and a sprinkle of ash from the wood burner. Mix well, and bag up ready for use.
Some will say it's best to use sterilised compost, but I find I get very little trouble from fungal disease, and a few weed seeds do not bother me. I also do not wash out pots or seed trays, shock-horror!
Any seedlings that die from disease are weaklings, and no good to me!
Title: Re: Making your own potting compost
Post by: lincsyokel2 on February 24, 2010, 20:52:38
I do buy some compost, but I recycle it as much as possible.
At this time of year I'm just about due to make up my mix for the busy spring period. The main ingredient is all last year's spent seed compost, and compost from any old pots, and spent compost from a neighbours window boxes, which has all been stored overwinter in a bin. I start by removing any roots and crocks, then add about half as much new compost, a couple of shovelfuls of garden soil, maybe some builders sand if any can be 'aquired', and finally a handful of organic fertiliser, and a sprinkle of ash from the wood burner. Mix well, and bag up ready for use.
Some will say it's best to use sterilised compost, but I find I get very little trouble from fungal disease, and a few weed seeds do not bother me. I also do not wash out pots or seed trays, shock-horror!
Any seedlings that die from disease are weaklings, and no good to me!


The two biggest problems in making your own compost are a) knowing the pH and b) knowing the nutrient levels.

The first one you can determine with a pH testing kit, the second one is much harder to do without a lab test.

Nutrient levels are measured in the rough by the conductivity of the compost, measured in micro siemens per metre (uS/m). As a rule ,used compost is around 200, unused soil id 350. New retail compost is about 500 and professional growing media is 600+.   If you make up a home compost bin,  putting in the usual kitchen waste and garden clippings, and leave it a year, the conductivity will be about 2000 - technically is known as a conditioner, because its too 'hot' to grow anything in. You need to get the conductivity of the home mixed final product to about 600, so you need to mix it about  8 parts home made to one part compost bin conditioner.

Consistency is all when making your own, otherwise the whole thing becomes too hit and miss.

If you want to tinker with the science, heres an interesting in detail explanation of EC
http://ohioline.osu.edu/aex-fact/0565.html
Title: Re: Making your own potting compost
Post by: Vinlander on February 24, 2010, 21:59:37
If you sow seeds like toms, peppers etc. that need high temperatures then try and find a takeaway that sells food in clear microwaveable trays.

You can fill them with any recycled compost and microwave them as if it was a meal. Then it's sterile and when it's cool you can sow straight into it, put the lid on and guarantee that any damping off came from the seeds.

Some people swish the seeds in bleach solution to make sure - but I don't know the right strength (problems are very few with this method anyway).

When they emerge you can prick them out. The clear lid means it's no disaster if you're a few days late.

If you can spare the trays you can perforate the bottoms, remove the lids and leave the seedlings to grow on.

Title: Re: Making your own potting compost
Post by: Spudbash on February 25, 2010, 15:24:11
There's a lot more to this composting lark than I'd imagined. Thank you all very much for your tips.  :)
Title: Re: Making your own potting compost
Post by: Ian Pearson on February 25, 2010, 17:20:19
Most composts (growing media, to be clear) you see now nowadays call themselves 'multipurpose' meaning that they are intended for seed raising, and potting. 'Back in the old days' there was either potting compost or seed compost, with the seed compost having lower levels of nutrient, the theory being as I understand it, that this encouraged good root development. I suspect using 'mutipurpose compost' for seed raising may make the seedlings 'soft', and possibly increase problems with fungal disease.
Treat seeds mean, I say - slim pickin's nutrientwise, and plenty of bacteria, fungi and assorted microbes to toughen 'em up and deselect the weak.

Obviously it's a different matter for potting on. There needs to be enough nutrients to last for the time that the plant will be in the pot. Preferably slow-release, otherwise most of it gets washed away the first time you do a heavy watering.
Title: Re: Making your own potting compost
Post by: lincsyokel2 on February 25, 2010, 17:42:57
Most composts (growing media, to be clear) you see now nowadays call themselves 'multipurpose' meaning that they are intended for seed raising, and potting. 'Back in the old days' there was either potting compost or seed compost, with the seed compost having lower levels of nutrient, the theory being as I understand it, that this encouraged good root development. I suspect using 'mutipurpose compost' for seed raising may make the seedlings 'soft', and possibly increase problems with fungal disease.
Treat seeds mean, I say - slim pickin's nutrientwise, and plenty of bacteria, fungi and assorted microbes to toughen 'em up and deselect the weak.

Obviously it's a different matter for potting on. There needs to be enough nutrients to last for the time that the plant will be in the pot. Preferably slow-release, otherwise most of it gets washed away the first time you do a heavy watering.


1. The low nutrient level in seed compost is because quiet simply any compost with an EC above about 1000 is too 'hot' for seedlings, and the massive ion flux into the root cells walls destroys the roots,  referred to as 'frying' the roots.

2. This is why professional growing media usually has either a 6 or 9 months CFR (Controlled Release Fertiliser) in it, or its watered with  a liquid feed at regular intervals. Retail compost is inferior because it has no form of nutrient control other than the nutrients  in it when you start - consequently professional growing medium is much more expensive, but then spectacularly better..
Title: Re: Making your own potting compost
Post by: tonybloke on February 27, 2010, 17:44:14
1. The low nutrient level in seed compost is because quiet simply any compost with an EC above about 1000 is too 'hot' for seedlings, and the massive ion flux into the root cells walls destroys the roots,  referred to as 'frying' the roots.

Not quite!!


seeds have in them sufficient food stores to start growth. most seeds will quite happily germinate and start growth in sterile media, such as rock-wool,  perlite, or vermiculite.
Title: Re: Making your own potting compost
Post by: laurieuk on February 27, 2010, 23:04:27
Wow :o all these technical details when I started as a boy back in the 40 s we had to make all our own composts. Gardeners would have their own mixes for different plants, We stacked turf to rot and use as the basic loam, always pulled apart so that the fibre was not riddled out. Charcoal from the bonfire, leaf soil,sharp sand etc. We used the basic JI formula which I think was 7-3 2 and various fertilisers.
Title: Re: Making your own potting compost
Post by: lincsyokel2 on February 28, 2010, 10:07:17
1. The low nutrient level in seed compost is because quiet simply any compost with an EC above about 1000 is too 'hot' for seedlings, and the massive ion flux into the root cells walls destroys the roots,  referred to as 'frying' the roots.

Not quite!!


seeds have in them sufficient food stores to start growth. most seeds will quite happily germinate and start growth in sterile media, such as rock-wool,  perlite, or vermiculite.
True, but thats not the primary reason why seed compost is made with low nutrients. High levels of nutrient WILL fry seedlings, ive seen happen on an epic scale at a nursery specialising in snowdrops and violets when they were delivered the wrong compost.

By  extension, it shows you how low the nutrient levels in retail multipupose compost are by the fact you can grow seedlings in in.
Title: Re: Making your own potting compost
Post by: caroline7758 on February 28, 2010, 10:26:42
. most seeds will quite happily germinate and start growth in sterile media, such as rock-wool,  perlite, or vermiculite.

I've used peat-free multipurpose mixed with perlite (roughly 2:1) for the last few years for seeds and found it pretty successful. I usually cover with vermiculite to stop the compost drying out.



Title: Re: Making your own potting compost
Post by: lincsyokel2 on March 01, 2010, 16:16:27
. most seeds will quite happily germinate and start growth in sterile media, such as rock-wool,  perlite, or vermiculite.

I've used peat-free multipurpose mixed with perlite (roughly 2:1) for the last few years for seeds and found it pretty successful. I usually cover with vermiculite to stop the compost drying out.





You might also try using hydroleca  on top once they seedlings get going, as it will hold more water for its volume.

Did you know there's only two place in the world where there's perlite ore? South Africa  and China, and the chinese mine has 80% of the worlds reserves. So when it closed for 4 months in the winter and everyone started to run out of ore, the price of perlite went through the roof. Its now producing again, so hopefully the price will come down again.
Title: Re: Making your own potting compost
Post by: Wilder on March 04, 2010, 13:50:27
that explains why my last bag of perlite cost £20. I nearly dropped on the spot!

I love bits of what some idiots call "useless information". How can information be useless???
Title: Re: Making your own potting compost
Post by: tonybloke on March 05, 2010, 19:47:16
perhaps another reason that seed compost is made with low nutrient levels is so the manufacturer doesn't have to purchase the nutrients to add?
Title: Re: Making your own potting compost
Post by: lincsyokel2 on March 05, 2010, 20:28:03
perhaps another reason that seed compost is made with low nutrient levels is so the manufacturer doesn't have to purchase the nutrients to add?

Nah, the cost of adding a 7-7-7 fertiliser to get the EC to 500 in a retail multipurpose compost mix  is here nor there relatively speaking.  Remember that many of the  compost makers dont buy fertiliser, they buy raw materials (like urea and rock phosphate)  and make there own.

On the other hand the cost of compensating a grower for 20,000 african violets because the seed compost you supplied to the grower was too hot and fried the seedlings would run well into 5 digits. Only from that point of view is it cheaper not to put it in the mix !

Title: Re: Making your own potting compost
Post by: tonybloke on March 05, 2010, 21:43:24
perhaps another reason that seed compost is made with low nutrient levels is so the manufacturer doesn't have to purchase the nutrients to add?

Nah, the cost of adding a 7-7-7 fertiliser to get the EC to 500 in a retail multipurpose compost mix  is here nor there relatively speaking.  Remember that many of the  compost makers dont buy fertiliser, they buy raw materials (like urea and rock phosphate)  and make there own.
On the other hand the cost of compensating a grower for 20,000 african violets because the seed compost you supplied to the grower was too hot and fried the seedlings would run well into 5 digits. Only from that point of view is it cheaper not to put it in the mix !
I have a friend who grows 1.5 million units per yr, got a 'bit peeved' when his compost (sinclair) was very low in N, (too much wood) it put him back almost a month with his schedule.
Title: Re: Making your own potting compost
Post by: genlistlass on March 06, 2010, 04:52:34
Last year I got myself a Flymo Pac a Shred garden shredder (slightly damaged plastic bin but usable) on the internet for under ? £90. Usually they are £200-£170...... I'll see if I an find the link for these.

Used it on woody twiggy bits in the late summer/autumn and just threw the shreds on the scruffy bit of my garden behind the raised veggie patch where the big weeds grow. I just trod the weeds down before I threw the shreds on.

Looked at them two days ago and all the tall weeds have gone and now there is a nice layer of composting looking stuff. So will chuck that over the veggie patch soon plus some alpaca poo from the stud up the road.

As you can see, I make it up as I go along  ;D

Gen in NBL where it is a balmy 4.5C at 5am !
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