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10 CONCERNS ABOUT PLANTING IN GRAVEL GARDENS AND OTHER AGGREGATES
POT'S GROWING ON? 22/09/23
In previous newsletter articles Changing soil composition = bad (2021) and 7 predictions for 2023 I shared my concerns about the trend for covering entire garden planting areas with aggregates. I thought it was worth expanding on these concerns as a discussion point because the trend is building steam and that worries me for the potential harm it may cause. This is more to share my concerns to discuss with you all than a ‘these are the facts’ article and it’s definitely not saying we cannot use gravel at all, so please take it in that light.
To be clear up front, all hard landscaping comes with a sustainability cost and as a surface to walk or sit gravel is pretty good sustainability wise. It lasts a fairly long time, is porous allowing water to drain into soils, doesn’t pollute ground and water like astro turf and doesn’t involve cementing in place. I’m definitely not saying gravel shouldn’t be used or that no gravel gardens should exist at all. I’ve added gravel for paths, small seating areas and over the top of a couple of small areas of planting myself.
But as a garden planner and wildlife lover I have been increasingly alarmed at the way gravel and other aggregates like sand are being positioned as the answer to gardening in an unpredictable climate in the UK. It feels like another attempt at throwing money at a quick fix to reduce effort while causing unnecessary harm to what was already there, ignoring what nature is telling us.
10 concerns about planting in aggregates
1) Aggregates change soil conditions
Gravel, sand, recycled crushed concrete, they all immediately change what is already in that area. The thicker the layer, the more change occurs. This could potentially wipe out whatever ecosystem was living on that spot before. We can’t see all wildlife and while the Soil Association estimate in 2006 that 25% of life on Earth lives in soil, a new study suggests,”soil is likely home to 59% of life including everything from microbes to mammals, making it the singular most biodiverse habitat on Earth.” While a thick layer of aggregate, especially without a weed suppressant matting layer, doesn’t stop life in the way Astro turf or paving will, in fact, much wildlife thrives in free draining bare aggregates, it does change what is there. In the UK, this is often a thick layer of vegetation, organic matter and animals that live and feed in this.
2) Artificially stops a natural cycle
Leaf fall and decaying organic matter feeds soils. In a gravel or sand garden, dead plant material needs to be removed otherwise it will start to blanket the gravel in a layer of composting plant material. In most UK gardens, even down south, this means a large area of aggregate cuts out this natural cycle of growth, death and decay, further changing the composition of this area. Essentially, aggregate for ornamental plant use goes against everything we have learnt about not disturbing or digging soils in recent years.
3) Gravel and sand won’t prevent weeds longterm
If you want to prevent unwanted seedlings, aggregates is not the answer, at least not longterm. According to the MetOffice, although UK summers are predicted to get hotter and drier, on our island surrounded by sea, winters are already beginning to get milder and wetter, even in the south. Over the next 50 years we will see winters become 1 - 4.5C warmer and 30% wetter. These are perfect conditions for winter growth and gravel is an ideal seed bed for hardy plants (I’m looking at you couch grass and dandelions). Even with thick layers of aggregate, beneath you will almost certainly have soil somewhere for roots to reach. Overtime, moss will grow in winter and build up layers of organic matter, further encouraging seedling germination and growth. Essentially, gravel and other aggregates are probably a short term fix for reducing weeding but longterm a false and costly quick win for most people.
4) Gravel and sand are a finite resource
Stone is not renewable, there is only so much gravel in the world and it is extracted from natural environments. Gravel tends to come from river beds (existing or ancient and dry) or as a waste material from quarrying other stone products. True there is a lot of it, but let’s use it where it’s essential. With 8 billion people in the world, potentially all wanting to use gravel, this is a significant impact on the natural world. It’s the same situation for sand, we use a lot for building, it doesn’t feel sensible for me to begin using mass amounts of aggregates in the garden where it isn’t essential. Waste materials are good for recycling but again are a finite resource dependent on original use of non-renewable products.
5) We can’t gravel every UK garden
Transporting gravel for what I would describe as essential use on some paths and seating areas is one thing. Transporting it for unnecessary plant use is another. Imagine the volumes of aggregate transported to cover vast areas of planting to 10cm depth or more. The majority of gardens cannot and should not be covered in gravel planting areas. Instead I would like to focus on the wild way of gardening, helping people weather the storm of climate change by studying and observing and showing examples of what works and doesn’t in our existing soils.
6) Ignores plants that may cope in existing conditions
We are only just at the start of climate change, things are going to get even more unpredictable. Before we throw away everything and start again, we should be studying what plants around us do in the existing conditions. Which plants thrive in hot summers and wet winters in our existing soils? What techniques help us manage that? In the last ten years I’ve already observed a wide range of wild and ornamental plants that have proven very able to tolerate extreme drought in summer as well as increased winter wet in the UK’s existing soils (I discussed some in Wild about Weeds).
7) Needs replenishing
Stones will last for thousands if not millions of years, obviously, but over time, gravel mixes with soil and organic matter and sinks, needing replenishing. Some people will add a layer of weed suppressant matting first to slow the process but I would never recommend this for planting areas because you set yourself up for a future nightmare as stuff grows over and through the matting, in time making it near impossible to weed.
8) A waste of people’s money
If planting doesn’t need aggregates why spend fairly large amounts of money buying and transporting it?
9) Celebrating gravel and sand planting encourages more to follow
More people using gravel causes more issues with soil, more unnecessary transportation, more unnecessary cost. Imagine if half of gardens began to be changed to gravel gardens. At what transport cost, at what cost to the existing wildlife?
10) Could harm some wildlife
As an obvious example, can birds access worms and grubs as easily from a 10cm+ layer of gravel compared to soil? Can newts, toads and frogs dig into gravel? I’m sure there are other examples.
Known positives of aggregates
I can’t talk about my concerns without talking about some of the proposed positives too:
1) Recycling waste materials
There are lots of waste materials such as concrete, stone and brick from old buildings, glass etc. These can all be crushed and used as an aggregate, it certainly saves them from going to landfill. But I would argue it’s on the construction industry to find a use for these within buildings, not to change garden soil ecosystems with them.
2) Creates new habitats for wildlife
Undoubtedly gravel, sand and other aggregates that keep areas of soil bare are useful for wildlife too, such as ground nesting bees and wasps. Adding the correct mix of planting can establish a good mix of diversity. But what existing habitat and wildlife were sacrificed for that?
3) Can suppress unwanted plants in the short term
For the first 5 years or so, a thick layer of aggregates can suppress unwanted plants as long as you put the effort in to remove seedlings and dead material each year. After that, please keep me updated on how much weeding you have to do.
4) Locks in moisture
A thick layer of aggregate will slow moisture evaporating compared to bare soil. But we cannot cover the whole of the UK in aggregate, making me more interested in what plants will thrive in our existing soils and which plants create evaporation preventing ground cover.
5) Can look beautiful
There is no denying that gravel gardens can look absolutely stunning. I too am drawn by the feeling that we have been transported to warmer, drier climates with the light tones of stone next to beautiful planting. Yet whenever I am in these spaces, I look around and am reminded that this is not what the UK is like on the whole, that they are a novelty in place of much life before.
…the current gravel garden trend is frustrating to me because it feels as though some people once again are searching for a quick fix to throw money at, rather than putting effort into understanding how nature works in the garden, ignoring what the wild ways can teach us.
The natural world is facing a rapid change in climate, many species may not be able to keep up, and I do agree we should be experimenting with helping those species that will struggle through loss of habitat. But we have to be extremely careful before we declare something a solution when it could potentially cause more harm than good in the wrong hands.
Gravel, sand and other aggregate gardens are interesting as homes to wildlife that need those habitats but I would much rather see everyone working to protect the wild habitats that already exist.
Also looking to incorporating habitats into usable areas such as paths, rather than wiping out existing habitats in planting areas to be replaced with another one.
I’m willing to be wrong, and I hope that most people see the trend more as a number of beautiful gardens that don’t necessarily mean all gardens will become like that. The wild way is an ongoing research project and experiment for all of us to explore how nature and the wild work in gardens. Starting by standing back to look at what is there now and collaborating with it.