Gravel and stone chippings – known in the business as ‘decorative aggregates’ – are possibly the most under-rated of building materials! They have so many uses we think every garden needs some. The knack is picking not just the right colour but the type of stone to suit what you want to use it for. Here is our summary of the best uses for decorative aggregates and the best choices for each use.
Mulching your beds and borders serves many useful purposes. Not only does it look attractive but it helps suppress weed growth, it helps with water regulation and retention, and it can help prevent soil erosion. There are many organic materials you can use to mulch – bark, straw, leaf mould – but all of these will eventually break down and need replacing. Natural stones have the advantage of a longer life and a better choice of colours!
To mulch with gravel or chippings, plant as you would normally and level out your soil. Spread a 2 inch (50mm) layer of your chosen aggregate over the soil, leaving a small circle around the base of trees and shrubs clear. We’d always recommend using a weed membrane underneath your aggregate. Not only does it help to prevent weeds coming through but also help to stop the aggregate sinking into the soil. It’s still easy to plant into afterwards, just scrape back your gravel and cut a cross into the membrane.
Although rockeries have gone in and out of fashion over the years, dry gardening is becoming increasingly popular. The latest buzz word is ‘xeriscaping’ – the practice of landscaping with minimal water use, to reduce or remove the need for irrigation. Popular in desert locations like Las Vegas, there is much the English garden can learn to adapt to climate change.
If you fancy a full-on rockery, with big rocks, it’s worth consulting professional landscaping designers on how to build it to ensure it is structurally sound and has appropriate soil pockets for your plants. However, planning a gravel or scree garden with perhaps the odd decorative boulder isn’t much different to using aggregate as mulch. Level the soil after you have planted, lay the weed membrane and spread the aggregate) to about 2 inches (or 50mm) depth.
Aggregate has multiple advantages if you’re planning a small pond or even a large lake! Firstly, if your pond is dug into the soil, it can help prevent erosion. A handful on top of any pots you plan to submerge will also stop the soil floating away. Aggregate is great for covering the base of recirculating fountains and at the bottom of ponds for plant roots to anchor to. Spread around the edges of a pond, water splashing on gravel or chippings can look almost glass-like and really set-off any marginal planting.
When choosing aggregate for use in water features, there will be several factors you want to consider, not only its colour. We wouldn’t recommend using aggregate alone under the pond liner as there is a risk of it puncturing; use sand immediately under the liner so there is no risk of punctures and it’s easier to level out. For the bottom of ponds pebbles or small cobbles would help weigh the liner down while giving little critters and fish somewhere to hide, it’s also worth picking an aggregate that has been washed so your pond isn’t full of dusty residue (there may still be some residual dust on them); whilst this will settle eventually, it may leave your water cloudy until it does. It’s also a good idea to choose ‘fish friendly’ aggregate, whether you intend to have fish or just wildlife visiting you, so it’s non-toxic.
If your garden is prone to collecting watering, either on paving or due to heavy, clay soil, the simplest solution may be to call in professional landscapers. However, there are things you can do yourself to help with drainage issues. Digging a mixture of organic material and grit/sand will help break up heavy soil (although could be a big job if you have a large garden!) Other options are to add drainage trenches, such as French or Herringbone systems, that use cheap aggregate to move water away from the garden.
You could use almost any aggregate for this purpose as it is predominantly doing a practical rather than a decorative job. There is perhaps an argument for going for the cheapest, most hard-wearing type, particularly if it’s going to be buried in a hole or trench. However, if you’re going to see it, you will want to think about its colour and shape in your garden too. If you’re laying gravel to help prevent soil erosion, something with angular edges may be better at catching soil particles.
Decorative aggregate can be much quicker and cheaper to lay than paving slabs or bricks, provides better drainage and has that satisfying crunch as you walk on it. However, we have all seen badly laid paths and drives, where they have become uneven and there are more stones in the gutter than on the drive! The key is getting the foundations right first and then in your choice of aggregate.
As a foundation for a path or drive, dig down at least 6 inches (15 centimetres) below the level that you want the surface of the path to be. Consider installing some edging, like cobbles or narrow bricks set in concrete, to help prevent your gravel spilling out. Then, fill in all but the last 2 inches of your trench with some hardcore; either large stones, broken house bricks or similar (scalps (Type-1)). Compact this down well. You should add a weed suppression membrane at this stage, then add your chosen layer of aggregate. There are many to choose from but a good choice can be chippings that lock together or are ‘self-bonding’.
A decorative border can add some real personality, texture and contrast to your garden, providing a foil for your plants or softening the edges of hard landscaping features. Using gravel or chippings can break up a large expanse of paving or flagstones, for example, and allow you to plant into it. If you have a fire pit, chippings will provide a more stable, fire-proof surface for it, not to mention a great colour contrast.
Getting the colour and size of your aggregate right is perhaps the most important decision here. Using an aggregate that’s the wrong size will stand out and look unsightly compared to the rest of the garden. For example, choosing a smaller aggregate for a long thin border will work better then oversized cobbles, whereas a 40mm slate will give you more interest over a large area then 20mm slate would do.
Best aggregate for edging and filling:
Gravel, sand or hardcore play an important part in the composition of concrete. As well as being a filler to bulk up the mix, the amount of gravel will determine the strength and texture of the finished concrete. Typically, aggregates like these form between 60% and 80% of a concrete mixture. Concrete alone wouldn’t have as much structural strength.
Arguably, if you’re going to mix your gravel with concrete, you probably need quite a lot of it and you’re not going to see much of it, so perhaps the cheapest option is the sensible one here. However, if you are going to polish the finished surface (something called terrazzo), you might want contrasting specks of colourful marble or onyx black showing through.