Mulch: for plants and soil

In brief, what are the benefits?

  • less weeding, and the weeds that do manage to grow are easier to pluck out of loose chippings rather than proper soil.
  • less watering in times of drought, as the mulch will retain water.
  • slow, permanent soil improvement, as the mulch degrades over time.

However, there’s a lot that isn’t said about mulch and mulching – I only realised it when, ages ago, I was listing it as a job for the day on my social grouping, and over the next few months had regular questions come up about it. It was only then I realised how much there was to know, and how much I (kind of) knew, but didn’t know I knew.

First of all, the basics. Get rid of as many weeds and their roots as you can – in as wide an area around your site as possible, you’d be surprised how far roots travel underground.

And of course, right away, there’s our first exception: if you’re practising no dig in raised beds, there’s a recommendation to just lay layers of cardboard down on top of whatever grass etc is already there, and then lay new topsoil on top of that. The grass will die and add its nutrients to the soil, without you having to expend all that energy digging it up.

Another exception is seedlings, or even small plants. There isn’t much point mulching them – they’re so small, they might be damaged by the pieces of whatever it is that you’re using, and there isn’t much space between them in any case. Plus, in the case of seedlings, you’ll soon be transplanting them. No, mulch isn’t needed, or even helpful, in this kind of situation.

Anyway, after you’ve got rid of the weeds and roots, feed the soil: the contents of used teabags (the teabags themselves are nearly always part-plastic, don’t use them), crushed shells from the beach (a hammer, with eye protection, is necessary, I warn you), washed seaweed, leaf mould, grass clippings with no seeds in, roasted eggshells, shredded waste paper with no colour inks used – shredded paper can’t currently be recycled by many councils, so you’re doing good here), your own home made compost, bought in topsoil, all sorts of things. If you have very small thin twigs or leaves from the shrubs around you – leave them there, on your soil! They’ll decompose down. For me, that means dead holly leaves, bare mahonia twigs, the privet leaning over my fence from next door, the soft tips of my buddleia plant, those sorts of things. Just use pieces that are the same size as your chippings – much bigger, and you’ll be creating a haven for slugs and snails.

I’d made an assumption in the past that the wood ash from my little incinerator would be a great addition to any soil – and I’ve already scattered the results of several small burns onto my garden, to no great harm. However, the RHS are wary, especially for fruit so a bit of research is a good thing. GrowVeg have detailed instructions about when it can be used, which is helpful.

I was very surprised, I must say, I couldn’t imagine how it could be anything but good, but proportions of nutrients “provided” by wood ash versus “needed” by plants can’t be argued with. Wood ash seems to be best used to correct acidic soil, or on the compost heap, and not in massive quantities.

Water is the final addition, if your soil is at all dry – because mulch is so efficient, if the soil’s dry, it won’t be a good growing medium. Getting the set-up right is really important.

Finally, lay the mulch! A little space around stems, so nothing rots, and you’re there. Enjoy the extra time your mulch will grant you!

Temporary mulches

These are most useful, to my mind, when you’re clearing a larger patch, and want to take care of areas you’ve already cleared, but not yet plant anything in those areas. And also, they’re good around annual and catch crops: you’re going to be harvesting plants and creating more planting, so digging up fresh, bought-in bark chippings (which are a fair cost over a whole garden) isn’t a good idea. If you have to walk on the soil, it will help spread your weight, which helps avoid compaction. So this means anything like thick cardboard, maybe carpet (100% natural offcuts free from a carpet shop, preferably, not nylon with threads that will disintegrate into your soil). My most recent temporary mulch is from when I had my kitchen done last month: the tradesmen had put down this kind of floor protection. I’d never buy it, not nowadays, but it was in my house and it was going to be thrown away. So I kept it, specifically for use as a temporary mulch.

A temporary mulch, even of a minimal thickness, will still weaken any leftover weeds, but if it’s impermeable, you should also note that it may well act as an attractant for weed roots nearby: when you lift it, you might find a lot of weed roots growing as near to the surface as possible. Keep an eye on it.

Please don’t forget what you’ve done, and end up letting a temporary mulch like this become a permanent one, that can leave you with a very nasty situation. You end up with a very thin layer of freshly formed soil, underneath which is a nasty mix of plastics and weed roots. Not good. But if you use temporary mulch in the way you intended, it’s really helpful.

Permanent mulches

To me, environmentally, a permanent mulch should be made out of plant material: either bark chippings, the most common, coconut fibre, or possibly cocoa beans. Bark chippings are pretty standard, they’re the ones I use.

Cocoa bean mulch seems more problematic. It’s wonderful to think of a use being found for something previously discarded as “waste” but the hundreds (thousands?) of miles it has to travel make it instantly suspect to me, especially when there are local alternatives. And users are very split about the benefits, even the lovely smell, which seems to get a bit much for some people after a while. The comments on the gardening blog are interesting for that.

Coconut fibre mulch has to travel as far as the cocoa bean mulch, I’m fairly sure, though at least it’s transported in a dehydrated form, as coir bricks.

There are other mulches, of course – slate chips, for instance. I have some, left over from a relative’s garden work, and they’re sort of useful in that when they disappear down into the soil when you dig, they create a bit of space and drainage: for clay soil, that’s valuable in it’s own right. But they give no nutrients to the soil, they’re just … stone … definitely decorative, and potentially useful, but they need to be in a patio area or the like, where they won’t be mixing with soil. Your Mileage May Vary!

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