Mulches Pros and cons - Part II: inorganic mulches

Following on from my article on pros and cons of Organic mulches, now we can have a look at inorganic mulches - that is, anything used as a mulch which does not biodegrade.

Inorganic mulches fulfil much the same roles as organic ones: they retain moisture in the soil, they suppress weed growth, they keep roots cool, by shading them from the sun: they also look lovely! The only thing which inorganic mulches don't do, compared to organic ones, is to gradually rot down into compost.

They are usually a lot more expensive to buy, but you only buy them once - well, sort of. Hmm, I should clarify that: organic mulches need to be topped up every year or so, because they gradually rot own into nothing. This does not happen with inorganic mulches, but that doesn't mean that it's a one-off purchase. 

Then you need to consider the knotty problem of whether to use membrane or not: I've written about this at length, so check that article out for details.

And the good news is that you can plant through shingle, very easily, even years after installing it. Just scrape back the mulch, cut a slit in any membrane, peel that back as well, then dig a hole, plant the plant, replace the membrane, and gently replace the mulch. Perfect!

They are not entirely "maintenance free" because they will eventually become host to weeds: you will either have to spray them with something like Pathclear twice a year, or you have to hand-weed them from time to time.  But generally speaking, they will indeed suppress weeds.

Inorganic mulches can be used in small areas, or they can become a major part of the "style" of the garden:

This sort of thing - left - is not to my taste at all, but if you don't really like gardening, this might appeal to you! 

(In which case, why are you reading my blog???!)

This garden, described as a "minimalist gravel garden", contains clearly delineated areas, using different coloured gravels, with rope-top edging stones to keep the areas segregated. Each area has one single piece of planting, plonked in at random.

I don't like this particular one - picture taken at random from the internet - because there are no clear paths: if I'd done it, I would have kept the planting to the dark areas, and kept the light ones as "paths".  But that's just my opinion.

This sort of thing is not quite as "low maintenance" as the designer would have you believe: plants shed leaves all year round, and you will need to clear them up, otherwise the various gravels will become dirty.  And if your chosen specimen trees/plants require regular clipping, then you will need to clear up assiduously, otherwise the shingle/gravel becomes clogged with the dead foliage, which encourages the growth of weeds.

You also need a generous depth of inorganic mulch, otherwise the dirt - both washed down in the rain, and creeping up from above - will spoil the look of it.

Here is a prime example from one of "my" gardens, from some years back: the owners had planted Box hedges, with shingle between, but the shingle was skimpily applied, and they had never maintained the area, allowing clippings from the Box to lie on the shingle and rot, which encouraged further weed growth.

As you can see, not very pretty! Even after I'd carefully hand-weeded it, and raked out every spec of dead Box leaves, the shingle was still dirty and unattractive, and in the end I persuaded the owner that we needed to rake out every scrap of old shingle, lay down a membrane, and relay new shingle.

One possibly surprising aspect of shingle is that it is not a barren desert - far from it! 

In my own front yard, which is fully shingled, I have found worms happily living in the shingle, when I have had to scrape it back for any reason: even in the middle of summer, the shingle is invariably moist, once you get down a couple of inches.

And here are a couple of newts, happily wandering around the front yard. 

There is no grass, no pond, no beds, no soil, no water: and yet I have a yard full of newts. They seem to like lurking around the many pots which I have there, and they seem to find plenty to eat in the matrix of the shingle, which provides a million small, moist spaces for bugs, creepy-crawlies, and all sorts of edible goodies. If you are a newt, that is. 

Another excellent point regarding inorganic mulches is that you can walk on them all through the year: no more muddy shoes! You can just pop out, even in the rain, and move around the area with ease. 

Mind you,  unless you have really tough feet (Lesley, this means you!), they are quite unpleasant to walk on with bare feet,  unlike a lawn.

Let's run through a few of the more popular ones.

1) Shingle or Gravel - pretty much the same thing. 

Small bits of stone, some may be a bit sharp, some are more rounded. Quite cheap, especially if you order by the tonne bag, but you will need to have somewhere for them to plonk the bag down without blocking your own driveway, while you laboriously trundle it through to the garden. Cheaper shingle is one homogenous colour, a sandy-orange colour: or you can pay more to get "golden" shingle which is kind of multi-coloured, and a bit more interesting to look at.

It comes in two sizes - 10mm ("pea shingle") or 20mm. If you get the smaller stuff, cats will use it as a litter tray: you will also get the shingle stuck in the tread of your boots. Larger material, 20mm, is better behaved, and less attractive to cats.

Good points: quick, cheap, looks wonderful, very low maintenance.

Bad points: after ten years or so, it starts to look "dirty". Easily fixed by raking well, and/or spreading another layer on top.

2) Rounded pebbles, or Stones, or Cobbles

These are usually used in smaller area, mostly because they are very expensive to buy, and very heavy to move around. 

They are best used as a feature: they can be added to a shingled area to break up the expanse.

Here - left - is another example from the internet, showing how areas of pebbles provide different textures, and modify the possible monotony of a larger shingled area.

They can also be used to form a "river" or "dry stream bed" effect.

Or they can be used just by themselves, grouped closed around the base of planting.
 

Good points:  interesting shapes and textures, and they last forever!

Bad points: expensive to buy/

3) Slate 

This is a flat mulch - small, usually rounded flakes of slate, very nice for mulching the tops of decorative pots. They are available in slightly more unusual colours - purple, dark blue - and they are less noisy to walk on than crunchy shingle.

They can also be used for paths - left - as long as you make sure to have a solid boundary, otherwise the grass creeps in to the slate...and the slate flakes can "walk" out onto the grass, from the action of people moving along the path.

And yes, they also need weeding, from time to time:  I have written about Slate Paths at length!

Good points:  attractive, unusual colours

Bad points: expensive to buy, will still need weeding.

4) Rounded glass

This became terribly trendy a few years back: 

..and before you shriek in horror, the glass is rounded, so it's not sharp and dangerous, but I have to say that I don't really care for it much, myself.

I find it slightly too artificial!

As with all mulches, it really works best if it is firmly contained: in this example, left, there is a good high boundary on each side of the bed, to keep the glass in place.

You really wouldn't want it getting onto the grass, as the mower would then spit it out at high velocity, which could be nasty, rounded or not.

 A more appropriate use for glass mulch would be on decorative pots: this - right - is a small pot of miniature plants, and the glass mulch makes a lovely understory for the planting, as well as keeping the small plants clean, and enhancing their visibility.

Good points:  looks fab when it rains!

Bad points: it's glass! Inherently dangerous..

And there you have it, a few types of inorganic mulch, how to use them, and their various good and bad points.

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