When it comes to compost, how damp is "damp"?

I was working with one of my students, the other day, and we were potting on some plants: this means that they had outgrown their pots - the plants, not the student -  and needed to be "potted on" into larger ones.

This activity requires larger pots, and a decent amount of additional potting medium, to fill up the gaps in the pots. This "medium" can be multi-purpose compost, "organic matter" (which I always have to put in quotes, because it's the fancy PC name for farmyard manure, also known as cow poo), or topsoil, or even soil from your own garden.

I say "even soil from your own garden" because using garden soil - or "earth", as we know it! -  is not necessarily the best things for plants in pots: garden soil usually contains weed seeds, and often contains quite a few bugs, worms, creepy crawlies, etc, which can be a problem for plants-in-pots.

So it's usually best to use the pretty-much-sterile bagged stuff.

The Client produced a couple of old bags of assorted stuff: one was bone dry and dusty, one was lumpy and hard, one had a lot of mushroom-type white filaments growing on it, and the last one appeared to be garden soil.

We decided to mix them all up together, in the hopes that the deficiencies would cancel each other out, so the first job was to find an empty wheelbarrow. 

We started with the worst one, the bone-dry commercial multi-purpose compost. It's always best to "wet" this sort of compost first, before doing anything with it: as you will know if you grown things in pots, it is well-nigh impossible to re-wet commercial multi-purpose compost, once it has dried out: just adding water doesn't do it, the water runs off and through the dry compost, in a very annoying manner, so it needs a bit of special treatment.

This next part, by the way, also applies to newly-opened bags of commercial multi-purpose compost as well: always check it, before you use it.

How to check it? Apply the "fist" test: take a big handful and gently squeeze it: open  your hand, and if you can just see your finger-ridges in the clod of compost, it's perfect. 

Now, that's a bit of a tricky concept to explain in words, so I have just popped outside and taken some photos for you, to illustrate the process.

 

Here is my potting tray, half filled with some sieved multi-purpose compost.

It's been in the tray for a couple of days, so it's dried out: multi-purpose compost  dries out really quickly, so I try to only sieve as much as I am going to need on that day. But there's usually a bit left over, and it's not a problem, as long as you remember to re-wet it before using it.

This batch is clearly too dry - I can tell by looking at it, by the colour of it, but let's apply the fist test anyway.

I take a fistful of the compost, and squeeze it in my hand.

Then I hold my hand where it is, and open my fingers:

Look what happens - the dry compost just falls back into my hand, and some of it falls through my fingers.

This is Too Dry.

If your compost is like this (and ours certainly was!) then put some of it in a bucket or a potting-up tray, add water, and rub it through your hands as though making crumble, until it is just damp enough. If you don't know how to rub up a crumble mix, then shame on you *laughs*,  just mix it around with  your hands, rubbing it and stirring it until all the water is absorbed.

It's no good just pouring water on top of it - the water will "sit" in globules, rather like when they used to let us play with mercury at school. (Do they still do that? Are they allowed to?) So you have to work the water in, manually.

Here is my potting tray, I have added water, and rubbed it in, and in fact, if  you look closely, you can see that I didn't bother to do the outer edges, because I just wanted enough to get a photo of it, to show you all:  can you see how the far left and far right of the tray are lighter in colour, and dusty-looking?

That is the original dry compost.  The slightly darker, lumpier-looking stuff in the middle is the area which received the water.

 

Now I apply the fist test again: and in case you are wondering, the sun went in, which is why this photo is a different colour from the above! 

But you can still see the darker compost in the middle, and the lighter compost to the far left and far right. 

There is no trickery here, this is the same compost, honest!

 Perfect.

When I open my hand, the compost stays on the palm of my hand, and you can clearly see the ridges where my fingers were.

This shows that my compost is damp enough.

Having rubbed in some water to your compost, how do you know if you've made it  "damp enough", exactly? 

Do the fist test again: if it drips all over your leg, it's too wet: if it all falls apart in your hand, it's still too dry, add more water. 

Keep working more water in, until you get to that perfect dampness, where you can just see those finger-ridges.

Right, end of demonstration, and back to the plot: having made the multi-purpose compost into something usable, we then added the other material.

The garden soil one, we tipped through a sieve first, to remove stones and other unwanted lumps.

The lumpy, rock-hard one was also tipped through the sieve, and the lumps were crushed in our hands: any which refused to be crushed were put aside. The mouldy stuff, well, that's nothing to worry about, a lot of commercially-produced compost will produce what appears to be disastrous amounts of mould, or fungus, and although it may be scary looking, it's perfectly normal, as fungus grows when things are dark and moist, ie the inside of a black plastic bag. Spores are pretty much everywhere, they are in the air all around us, so a bit of "mould" in a bag of compost is nothing to be alarmed about.

Having mixed it all together (at this point, there may or may not have been a couple of choruses of  "you put de lime in de coconut, and mix dem all up"), we applied the fist test again, and decided that it was still a bit too dry, so we stirred in some more water, until we were happy with it.

Why go to all this trouble? Well, I'm sure you've heard all those nice little aphorisms about "you can't build a castle on shaky foundations", or "forewarned is forearmed", or "an ounce of prevention is worth a pound of cure", although that one ought to be "a gram of preparation is worth a kilo of cure" in these modern, decimal times.

The point is, if you try to pot on, or pot up, with dry, horrible compost (I use the word "compost" now, because it takes too long to write out the description of "potting medium" every time) then you will struggle: if the compost is bone dry, you won't be able to pack it firmly but gently around the plant, you will find yourself ramming it in, in order to hold the plant upright. This damages the delicate roots: and as soon as you try to water it, the compost will "boil" in the pot, and will froth up and bubble over the sides, while the water then leaps straight through and out, all over your feet.

But if you get your compost just right, before you start - ah, that's when potting up, or potting on, becomes pleasurable, because it is easy. End of lecture.

So there we were, with a wheelbarrow full of good "stuff": well mixed, and perfectly acceptable for potting up, potting on, and for top-dressing any pots whose soil level was getting a bit low. We had also made use of four half-bags of otherwise wasted material, which is ecologically sound: we'd cleared out four dirty, cobwebby, messy bags from behind the shed: and now we could instruct the Client to buy in half a dozen new bags, ready for use.

And the re-potted plants were very happy!

 

 

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