Friday 1 February 2013

Mulching with gravel and stone

Schizostylis loves the extra moisture under mulching stone

Many years ago a student said to me  “if you are so keen on zero cultivation, why don’t you put a mulch over the ground and gain a further whole series of advantages?” I do agree. Today, I will confine my comments to covering the soil with none water-absorbent stoney materials. Mulches in general, have many advantages, including conservation of soil water, weed control for ‘weeds-from-seed’ and provision of design opportunities. Plants just love the conditions created by stones and gravel. I have to confess that my secret belief is that the greatest benefit of mulch is that it prevents the over enthusiastic gardener scratching away at his soil!
I was first converted to gravel mulches forty years ago at Askham Bryan College when at the then annual conference for Parks directors, the speaker almost as a ‘throw away line’ mentioned how he mulched borders throughout his town with a two inch thickness of ‘pea gravel’ (purchased from a builder’s merchant it is still my favourite mulch). The revelation caused a mild sensation and he was bombarded with questions such as “what if you change your mind?”  “what about vandals using the pebbles as missiles?”  what about accumulating litter?”  “what if you have not eliminated perennial weeds?”
It never really caught on, but never-the-less you still see fine mulched landscaping, albeit more often with larger pebbles, mulching stones, small rocks and un-cemented paving.

Nerine, arum ophiopogon et al

The first gravel garden constructed at the college was a large educational display of ‘dwarf conifers’. The border was prepared conventionally and covered with thick black polythene!
The plants were inserted through slits in the plastic and the whole thing was covered with a thick layer of gravel. The conifers thrived for twenty five years and over that time no more than a total of a couple of hours was spent pulling out the occasional opportunistic weed. Visiting parties always asked “but how do they get water?” The fascinating thing is that they do! Water gains access through the planting holes and from the edge of the plastic. As a consequence of a repeating cycle of evaporation and condensation beneath the polythene the covered soil remains uniformly moist. 
In the end, the border suffered the normal fate of all so called dwarf conifers. It became a forest! 

On a Winter morning-today!

Nowadays people tend to use ‘mulching fabric’ rather than polythene. Although the use of gravel-covered plastic is anathema to me, it is an excellent labour-saving approach for fairly permanent more static landscape features. In the past I have created gravel gardens for clients who no longer wanted to mow their lawn. Its so easy, just spray off with glyphosate, cover with plastic, slit in nice plants and spread gravel. Hey-presto an easy garden feature that lasts for years.

The whole of my front garden is mulched with builder's gravel

Why I don’t use plastic 
The reason I do not use plastic in my own gravel gardens is because it is too restricting. I want  plants such as hardy cyclamen, creeping thymes and dwarf tulips to seed themselves. I want delicate alpines and hardy cacti  to spread. When I acquire a new precious plant I want to easily pop it in. Because I use glyphosate I do not need underlay to prevent weeds nor do I need to spread gravel at the usual  two inch thickness.

I plunge these golden torch cacti for eight months of the year

Choice of plants
Herbaceous, bulbs, shrubs, alpines, annuals and biennials, for me any category of plant will do. Gravel gardens are perhaps less suitable for dense plantings such as herbaceous borders, for vigorous vegetation and ‘plants that run’. I recently inspected a gravel garden where bamboo had taken over! (It was easily cured with a well directed glyphosate spray).

Gravel is a wonderful place for seed to germinate
Another Cyclamen coum taken today

Wonderful water conservation
We might forget in this wet year how precious is summer moisture (although the current fashion of planting-for-drought might fade more quickly than most gardening fads). All mulches have merit for water retention but I think  gardening literature fails to recognise  the superiority of gravel and plastic. Spongey materials at the soil surface will intercept light rainfall. Stone is none absorbent  and rain percolates through. Much of this water is preserved from subsequent sunshine and drying wind. I liken gravel to a one-way-valve for  water and I think this is the main reason why plants thrive when mulched with gravel and stone!

Winter aconites push through

I have recently written a more extended article on mulching


  1. Gardeners here tend to use gravel as a weed block (with a fabric weedblock under of course.) Our Summers can be rather scorching. The stones intensify the heat making it difficult for plants to survive. I do see how in cooler temps mulching with gravel may be a nice.

    1. Very interesting comment Carolyn. I have checked your profile and can imagine its hot up there! I have never found overheating of my plants a problem in the UK, even on the rare very hot day. Many of my plants are at what I would call a normal degree of ground cover and there will be some evaporative cooling of plant leaves as well as shade on the gravel. Rock gardens are quite popular here and I have never seen plants scorched as they scramble over the rocks.
      I see you blog as a grandmother. I am pleased to find that other seniors are bloggers like myself. (I have two grandsons Henry and Arthur)

  2. I made what I call a
    pebble garden last year but didn't use plastic as I wanted to add spring bulbs and other plants gradually. I'm looking forward to seeing how it develops this year.

    I also made a mini fernery last year but this will be mulched with bark as I don't think pebbles are appropriate aesthetically

  3. Your pebble garden and gravel really sets off your plants well. Plastic under cover would be completely inappropriate as it would be for my own.

    1. and I forgot to mention Sue that I use bark mulch too-particularly in my acid border.

  4. Plenty of food for thought there Roger - I have an area of gravel in my garden, for practical reasons it was graveled over. A few years later - was not one of my best ideas!!!
    I did put down a weed membrane and I have gradually been cutting holes and planting in it.
    I find that bark mulching is a harbour for slugs - having used this perviously, I vowed never again!!
    I agree with your comment re drought planting - should the wet weather continue - bog gardens will be all the rage this year :)

  5. I have never really noticed that bark mulches harbour slugs but I am sure you are right. I will be blogging soon about slugs and my theory that if they are just eating my decaying weeds and organic debris that I leave around(!) thats ok by me.
    Cher from Sunray gardens left a comment on my last post about all her fantastic hostas pictured on her blog -all mulched with bark!

  6. Nicely argued or the gravel. I mulch my veggie garden much to the amusement of the 'old style' garden teacher I work with! Found you via blotanical, off to subscribe and have a further nose. No slugs under wood mulch here, actually wood mulches don't hang around long in our climate, perhaps they take slugs windsurfing as the vanish?

  7. My friend Alan lives on Orkney. I know about your wind!

  8. The pink theme was unintentional Catharine, but I can see from your blog that you have the designers eye!

  9. You're right, I did enjoy this post, thanks for directing me to it.
    I think gravel around plants look nice and tidy, in the right setting, but for me it also serves many other purposes. I use white gravel with liner beneath in my deep window baskets in my front garden. After much experimenting it is the only thing that keeps the squirrels from digging there, and it works, no more peanuts in my window baskets!
    I also have a long gravel path with a fabric liner in my back garden, I laid it years ago and have never had to weed it. Not keen on plastic myself either, there are fabric liners from the very cheapest to horrifically expensive. I have steered clear of the pound shop ones after a few bad experiences and now go for the next ones up, which lasts me for many years.

  10. Hi Roger, a quick question - what do you do about feeding plants? I guess you don't add compost over the gravel?! do you just do good soil preparation before planting and then leave the plants to get on with it? I have very poor sandy soil and I suspect my plants would suffer over the years...

    1. Hi Rose
      My soil is sandy and I don't find I need to fertilise the soil. My soil preparation is not thorough as I am a no dig gardener! I have argued in my posts why my soil is in good nick without cultivating.
      IF your soil is very hungry use a general fertiliser- put NPK fertiliser in my search box - and anyway you could use growmore. Fertiliser is soluble and will wash in through the gravel.
      You will see in my posts why I believe valuable organic matter will increase in the uncultivated soil naturally,
      Nature will add more organic matter to the soil if you let her.
      Good to have your question Rose

  11. Hi Roger,
    Do you have any thoughts on the reports about the extremely harmful effects of Glyphosate on the enviroment? As a keen Gardener it would be great to get your take on this. Here's just one clip of thousands

    1. Hi Anon
      I find it very difficult to reply to enquiries which impinge on people’s life philosophies and belief systems. I therefore decline to open your link and debate what, as you say, is one of thousands of similar ones.
      The last similar link I opened started with the statement that millions of americans use glyphosate on their lawns. A lot of dead lawns then. If the other ‘facts’ were of similar provenance I have no wish to examine them all.
      My own position, I have already stated in my posts. In particular at a simple gardening level I have discussed them in ‘batting for glyphosate’. I have also argued that glyphosate which makes minimum cultivation systems possible worldwide has helped the soil to maintain its store of millions of tons of carbon and that soil erosion has been considerably reduced. Furthermore its economic effect has contributed greatly to enhanced level of efficient food and commodity production.I believe the world is a better place for the existence of glyphosate.
      I have been using glyphosate for nearly forty years and believe it to be an extremely safe material of zero toxicity. I am myself very healthy and look forward to a ripe old age. My plants are healthy in my minimum cultivated soil which is rich in organic matter, worms and other soil organisms. My gardens are havens for wild life and in particular insects such as butterflies and bees. Using my specific methods the garden is even rich in wild flowers and as I walk round my garden today can count about two dozen self seeded dactylorhiza orchids.
      I share prejudices against big chemical industry, pharma and the food industry. Even if you object to the demonized Monsanto, glyphosate is now out of patent and generic and is manufactured by numerous companies.
      For a chemical with worldwide millions (billions?) value of British pounds sales, glyphosate has a remarkably good safety record, but used on such a scale there are bound to be idiots who misuse it.
      I don’t want to persuade anyone to use glyphosate who does not want to and there are many readers of this blog who do not wish to do so. For myself I have no reservations of continuing to use it.
      I don’t know anon if your enquiry is a genuinely innocent one or whether you have an axe to grind, but anyway I hope my comments help!

  12. Dear Roger, I am 72 with a heart problem, 2/3rds acre garden. I have been looking at the article on mulching with gravel or bark. I note the info on plastic and slits and porous matting. I note your comments of not using in herbaceous borders(Big) I am also sandy soil (Lincolnshire) Weed supression (my health) is a good idea but concerned about it stopping my bulbs coming thru(Daffs,Tulips,Bluebells etc. But (Sigh) I really do need to cut down on the weeding! regards Jo

    1. Only 18 months late!
      No problem whatsoever bulbs coming through unless you have plastic! And even then if planted under the slit it will find its way.


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