|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|