Mulch is one of my favourite words — although I know it’s one that makes many people snigger. It’s such an important gardening job, however, that it should really be embraced. Mulch is a layer of material applied to the top of soil and is usually, but not solely, biodegradable material, such as spent mushroom compost, well-rotted horse manure and composted bark. You can mulch decoratively with non-biodegradable materials such as gravel, stone chippings or crushed shells. In fact, you can use just about anything you can get your hands on, including crushed coloured glass (if rounded off) or recycled rubber tyres if you like that sort of thing.
Mulching with organic matter is not just about making the garden look tidy and looked-after, although it does that too. A thick layer will significantly reduce weeding because it smothers annual plants and any seed that has failed to germinate, starving them of light. Pernicious perennial weeds grow through, so are easier to identify and dig out come spring. Mulch also retains moisture in the soil, locking it in and reducing evaporation and so reducing the need for watering. Plus, over a season it will break down to improve a soil’s structure and texture to make it more fertile.
If you mulch in the autumn or winter, by spring the worms will have drawn a lot of the material down into the soil so that you don’t have to dig it in. It doesn’t matter what type of soil you have, claggy clay or free-draining sand or limestone, masses of organic matter will improve it, allowing you to grow a wider range of plants more successfully. Mulch is commonly applied once a year, but serious gardeners do it twice. Over the years, if done religiously, you will develop a top-quality soil.
Decorative mulch such as aggregates (gravel/stone chippings), larger slate pieces, broken shells or a finer grit on alpine gardens, will also lock moisture in, feed plants’ trace elements over time and in summer keep the sun from baking a plant’s roots. From a design perspective, I find bare, light-sapping dark soil rarely the best medium to show off a plant. The choice is either to pack more plants into the gaps for a traditional border look, or to create the feeling of space by planting them farther apart — which calls for a material to mulch the soil in between to bring the composition together. Create informal paths to encourage people to walk through any generous gaps in the planting.
The type of mulch you choose is key to helping it to sit comfortably with the other materials in the garden. For example, chipped bark associates well with woodland gardens, but not dry Mediterranean-style planting. Mulch can also transform the feel of a tired garden area — a tonally light material such as beach pebbles or crushed cockle shells will bounce the light around and lift a dark shady space.
Organic mulches include wood chippings, chipped bark, well-rotted manure, leaf mould, spent mushroom compost (alkaline) and seaweed.
Landscape fabric (or geotextile membrane) bought on a roll is ideal for large areas because it can almost cut out weeding. It creates a physical barrier to stop weeds, but allows water to drain through it while stopping the soil from mixing with the mulch on top. Cut holes for any plants and then mulch over the bare fabric with a decorative material (chipped bark, gravel, slate chippings). It’s essential to pin the edges down (thick galvanised wire, cut and bent into U pins, works well), as well as where one layer overlaps another to stop it flapping up and looking unsightly. Balance the area out with plenty of planting so that it doesn’t simply look like a random sea of gravel.
How to apply mulch
Apply organic mulch only when the ground is wet and avoid building up around a shrub’s stem, or covering the centre of a perennial or any small delicate plants because this may encourage them to rot off. If you’re not sure you have enough material for an entire area, mulch around each plant and then fill in the gaps.
Mulch with a minimum of 5cm of organic matter on flowerbeds. With gravel and other aggregates, about 5cm is also a good depth, but you may want a little less for areas that you walk on so that you don’t sink into it. You will need about 50 litres of material for 1 sq m at 5cm deep. For larger areas look at getting a bulk loose delivery because it’s much cheaper.