Which Compost To Buy

which one...?

Buying compost for some, is possibly a little like me trying to figure which washing powder I am supposed to put in the supermarket trolley. 😉 It wasn’t always like that….

I couldn’t believe it when in the garden centre recently the amount of types variations in labells one could buy. It’s seemed extremely confusing to be quite honest.

I remember still, growing my first seeds with my grandfather and my second batch of seeds with my Dad. I would have been no more than 5 years old. This clap trap never existed. Never. It was a hand full of clay in a pot, possibly sieved and that was the end of it.

Golden rule number one: Do not get confused by what’s on the shelf. Gardening has been around for centuries and 150 years ago you couldn’t buy a bag of compost if you tried. Fact.

Before I go any further I must sidetrack, slightly so stay with me here: the pH scale is a range from 1 -14 which tells us how acidic or alkali [in this case] a soil/ compost is. For the moment/ example car battery acid would be on the lower end of the scale and milk would be on the higher end.

In theory, as it stands, almost all composts are peat [as in peat moss from a bog] based. Although the use of peat and amount of may change in the coming future. What one must appreciate is that peat has a low pH and is the basis for the making of almost all composts.

In basic compost terms there are two main types:

  • The first Ericaceous or acid loving – just two of the names it may come under and are pretty much peat mixed with a [slow release] fertiliser and a wetting agent. It comes with a pH of approximately 4.8.

Wetting agents are used because peat, when it dries tends to [kinda] combine, meet and muster itself together in one big clump. This is particularly visible in pots where it almost leaves a gap between itself and the container. When one tries to water and dampen the peat/ compost mass will simply float like a buoy or the water will just run off and down the sides.

  • The second type is compost. In any variation… from potting to multi purpose they are pretty much all the same. They are peat, mixed with a slow release feed and lime [or a substitute of some format] which will reduce the pH acidity.


The only thing that differs [generally speaking] from the compost used for potting trees versus that used for eg in growing bedding plants is the particle size in the peat and the duration that the feed will last. ie. trees will prefer a chunkier particle and will remain in the compost longer where bedding plants will only last about three months plus and the compost must be almost sugar granule size.

For those not in the nursey trade attempting to grow prize crops… or to put in context when I am at home growing my salads and herbs I simply grab whatever is available and failing that a handful of clay from the garden. The only honest difference between the ‘muck’ in your garden and the bagged compost will be the consistency at which the plant will grow.


As a by the way John Innes is a range of compost mixes. So if this multi purpose compost has added John Innes…. it’s either the man himself in there or [put in very simple terms…] it’s actually compost with added compost.

Technically you can call it something else. In the specialist nursery sector and prize winning plants one could argue…. But tell me I am wrong…?

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3 replies
  1. paysan
    paysan says:

    Nice post Peter. I remember my dad sieving soil to pot up his seeds. We used our own compost and if we needed something more robust for veggies we got manure from a farm…

  2. Peter Donegan MI Hort
    Peter Donegan MI Hort says:


    Thanks mate 🙂 I had to buy my compost with my pocket money from the age of 5 onwards…. I went to the libary and did my research and got smart pretty quickly 😆 I guess a grwoing medium is just that. 😉

    Happy memories

    beir bua

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