Straight well composted horse manure as potting soil

I will add that a year old composted manure still shrinks a lot. For personal pots that’s not a huge issue as topping off with fresh medium isn’t a bad thing. If on the other hand we are talking 50~100 pots to eventually sell, it adds a lot of unnecessary labor.

I’d mix it 50-50 with sand if sand was available.

I used horse manure as potting soil but didn’t have very good results. The plants displayed nutrients intake issues on the leafs. I initial thought it was too acidic so I add a spoonful of lime to the pile. After couple of years trying without much success, I recently googled its PH level. I am surprised to find that the horse manure is very alkaline, above 8. Most plants like acidic side. Maybe, mix horse manure with peat moss may lower its ph level


Don’t believe everything you read on the internet. I seriously doubt composted manure consistently reaches anywhere near that alkalinity. I know that stable waste doesn’t do so consistently and have even analyzed it via a laboratory. It came in an 6.3 with a nice balance of nutrients- but it originally contained more urine soaked wood shavings than poop, which would drive down the pH. Stable waste from a single stable, so hardly proof of anything. I find varying estimates on the internet for pure HS and 8 is the very top of the range.

My sister used to grow fantastic potato crops in garbage pails full of composted horse manure. It was in CA so she didn’t have to worry about great drainage, which would generally be a problem with using any kind of compost exclusively for potting soil.

I learned a bit looking this stuff up… for instance that most compost is either neutral or alkaline (as high as 8) but doesn’t affect the overall pH of soil very much.

The key danger of too much compost added to soils appears to be building up excessive P, which I had never read before.

I just share my personal experiences. I am not an expert on using horse manure, unless you are. No need for me to sample manure from different stables. Just a home garden use, got from the nearest stable. Another observation, the area that I spread horse manure around (trees trunk) grow less weeds for a year or so. It looks like horse manure suppress most weeds grow except Creepy Charlie. Horse manure I took was well aged with a lot of earth worms

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I learn from my experience, others and research based sources and find them all useful and fascinating, but believe they are all best taken with a grain of salt. Too many variables and not enough research, for one thing. As far as composted horse manure, I have used it for gardening for about 55 years and have never had anything but positive results. I’ve never heard of anyone running into trouble from using too much and creating excess P but, nevertheless, I found that warning in the link I provided both interesting and credible.

Alan, I must point out that your discussion is out of the scope. The topic is to discuss effects of using horse manure as potting soil. Mine shared experience also focused on using it as potting soil. But you are talking about using it in ground which could have very different result because the soil is the varst majority of the earth, adding a some horse manure into it, may not have major influence of the soil . On the other hand, in a confined container with major growing media is horse manure could have major effort on plants’ health. I appreciate you show studies with good result of using horse manure as potting soil

Potting soil at a pH of 8 would not work well and you should be grateful that I did the work to find out a more complete answer about the range of the pH of horse manure. I know I am grateful when I am correctly contradicted… but I’m 71 years old and whatever I haven’t proven yet I probably never will… except maybe that I can die bravely.

I should add that sulfur or peat moss could be added to get the pH to a more appropriate range if it tests anywhere near that high. While the studies show that it has little affect on the overall pH when added to soil, as a solo ingredient or even a major one in potting soil it would likely be a much different story- one should probably aim for a pH in potting soil of something between 5.5 and 6.5 for most plants.

Actually, rechecking my link, it wasn’t the one that had info about specific pH of horse manure but a lot of the info would pertain to using it as potting soil. However, a pH of 8 appears to be rare in composted manure and the high range extreme based on sources I could find.

Most sources report the pH of compost between 6 and 8, without specifying a source for this information. Reference 1 shows the pH of various composts and most are between 7 and 8. For example: yard debris 7.7, mixed manure 7.9 and leaf 7.2. The ones below 7 include horse manure at 6.4 and bark compost at 5.4. Reference 2 studied home composts and found a mean pH of 7.0 to 7.5.

That’s from this but other sources have similar info. Compost Creates Acidic Soil - Garden Myths

If you have a source that says horse manure regularly has a pH of about 8, I’d love to see it. I couldn’t find one.

There are many contradict info on the internet. I googled the PH level of horse manure. There are what I got from there different source/ websites.

How are those sources credible? What are they based on? I could find nothing from your links by which to evaluate the info. They seem to be businesses and not necessarily purveyors of sound info. except the one from Nova Scotia, which was apparently university based but you provided no link to it so I could see where their figure came from.

I found the source of the Nova Scotia thing and they were talking about fresh manure not composted.

I found the comment in it that if your soil is acidic, it will need to be balanced before adding the manure very perplexing. If they are saying pH of HM is 8 one would tend to feel safer applying it to acid soil, at least a slightly acidic one.

I asked my AI app and it told me the pH of HM was between 6-8. On Google scholar I couldn’t find any research directly addressing the pH of horse manure. I don’t think the question has been researched much at all. One research paper was based on using newspaper waste and horse manure composted together to make potting soil and claimed it worked well- but newspaper would presumably lend acidity to the mix.

I’ve come to the conclusion that the only way to know the pH of any given horse manure is to measure it yourself. Equestrian owner info suggests that the pH of the poop of any given animal varies a great deal and that measuring it is a diagnostic tool in evaluating the health of a horse.

All that said, it seems that if you address the pH issue and adjust it accordingly, composted manure should work well at least as a central ingredient in a home-made potting soil. Perlite and/or sand would be required to make the kind of mix I use. I use a compost made of woodchips and yard waste with equal parts by volume of peat most and sand or perlite. Works great for fruit trees. The compost alone has a pH of about 7.5.


@IL847, I had similar problem as you did, I don’t use horse compost anymore. I can get them very cheap here, and they are already composted.