Sage Advice

Getting started with composting

Callum Halstead

I have now been living in my new home for a few months, tending my plants and dreaming of what the garden might look like one day. At this early stage, very few of the choices about what I do next are my own. The elements are very much in control, and it would be foolish of me not to comply with nature's wishes. The garden is dictating where I should start, and what must be done in order to progress. Firstly, I must water, water, and water again. The blasting winds of the Fife coast strip moisture from my potted plants daily, often toppling them like skittles and scattering them across the lawn in the process. I had hoped to keep them potted for a bit longer, while I settle on a planting plan. However, it has become abundantly clear that the only way I can guarantee my plants' short-term survival is to get them into the ground, providing them with a larger rooting environment, good anchorage, and access to groundwater.

Over the past week or so, I've spent my evenings creating new flower beds to provide these plants with temporary homes. This is a physically demanding and time-consuming job. Having cut and lifted numerous strips of turf by hand, my flimsy wrists and elbows are all but ready to give up on me. But seeing my progress is galvanising, and I know it will be worth it. Keeping a positive mental attitude has been key, not least because the 'soil' I' m exposing from beneath the lawn is bone-dry and completely impoverished; it looks more or less like moon dust. I can't say that I' m surprised, as grass roots are notoriously efficient at soaking up every last drop of water in the soil. To prevent much of this bare and parched earth from ending up somewhere out in the North Sea the next time the wind whips up, I need to incorporate some good organic matter to improve the soil's structure, lock in some moisture and, crucially, transform the bed into somewhere that my plants will enjoy living while I make decisions about their permanent homes. The urgency necessitates that I buy ready-made compost this time. However, chances are that the soil will need to be improved throughout the garden— whatever I choose to do with it —so it looks like composting will be the next job on the list. The sooner I can get started on that, the better.

There are numerous options available to gardeners making their own compost, ranging from simple compost bays— cobbled together for free using salvaged wood and pallets —to more high-tech options, such as the very effective Ridan® food composting units. It's important to choose a compost bin that can handle the volume of material you are likely to generate. In my experience, it can be useful to have two or three bins, so that one can be filled while the others are busy composting down or being emptied, but I appreciate that this may be excessive if your garden is on the smaller side. A single bin can still be hugely valuable in helping to manage your green waste and providing you with good quality compost.

I have opted for a low-cost option by constructing three open-topped bays out of a dozen pallets, in which I will employ a 'hot composting' method in rotation— filling, turning, and emptying each bay in turn. However, the simplest and most straightforward method of composting is 'cold composting'. Here, compostable material is more or less just piled up and left to break down over a period of two to three years, without requiring you to monitor or turn the heap. This method is very low-maintenance, and the heaps require little in the way of labour to create. But a significant disadvantage is that perennials are likely to build up in the heap, unless you very carefully manage what material you are putting in. Cold compost heaps do not reach a temperature sufficient to kill off seeds, so this limits how the end product can be used. This kind of compost is good as a mulch or soil improver in the vegetable garden, where crops are generally grown in straight rows, making unwanted growths easy to spot and hoe off.

Hot composting, on the other hand, requires more attention. It needs to be turned at least once. The aim of the process is to encourage the heap to heat up and remain hot for an extended period of time. This is done by balancing the proportion of ' green ' and 'brown' materials that are added, and by increasing oxygen availability in the heap through turning it at intervals. The target temperature range for a hot compost heap to reach and maintain is 40-70°C, with an optimum heat of around 55°C. This will be hot enough to kill off unwanted perennials and seeds, but not so hot that all life within the heap perishes. A compost thermometer will help you keep a close eye on the level of activity within the heap as the material breaks down. Compost that is produced using a hot composing system is likely to be more even in quality, thanks to all the turning and mixing. The number of unwanted seeds that have survived the heat should be fairly low, leaving you with a very versatile end product that can be used as a weed-suppressing and moistureretentive mulch, or as a general purpose compost for potting and soil improvement.

When building any heap, it's a good idea to be intentional about how you layer the material, ensuring a regular alternation between green and brown. The breakdown of green, high-nitrogen material is what builds heat and gets the composting going, and then the brown, high-carbon material provides the fuel that sustains the process. The better layered the heap, the greater the likelihood of maintaining a constant high temperature— and the more efficient the composting process. As a general rule, aim to use around sixty per cent green material to forty per cent brown. During the winter months, there will be a great abundance of brown material and a general lack of green material. This shouldn't be too much of an issue, unless you have no green material at all. The key is to ensure that you get a sufficient amount of moisture into the heap. It's also beneficial to chop the brown material down into smaller bits if adding a lot at once. The smaller the brown material is, the less green material you will need in the heap in order to balance it. During the summer, the opposite situation can occur: the majority of the material that ends up on the heap is green. Overly green heaps can become very sludgy and do not create good quality compost, so it is worthwhile keeping aside a supply of brown material that can be added to the heap during the summer, to maintain a more appropriate balance.

As your heap grows, it's vital to try and ensure it remains evenly moist. Aim to incorporate water regularly as you build it, as it is very difficult to adequately and evenly moisten a heap once it has been built. Use water from a rainwater butt if possible— tap water will have been chlorinated to kill bacteria, and this will have an effect on the composting bacteria in the heap. Don't worry too much about this, though: the chlorine will dissipate quickly, and the bacteria will bounce back. The best method with tap water is to give the heap a good soaking every once in a while, and then leave it for a period so the bacteria can recover. Once your heap is half full, add a layer of fully rotted compost from a heap that you have recently emptied before adding more fresh material. This will have the effect of inoculating your new heap with the beneficial microorganisms that inhabited your last one, helping to hasten the composting process. To further speed things along, you can try to promote the build-up of heat in your heap— even in a cold composting system —by incorporating various materials that act as compost accelerators. These include fresh grass clippings, spent coffee grounds, and even urine if you are so inclined. If you live somewhere where you can get your hands on unprocessed sheep's wool straight from the farm, then I recommend you grab it with both hands. Wool is a very slow release nitrogen source, making it an extremely beneficial material to add between layers of brown material during the winter. Rather than bundling the wool straight into the heap, soak it in water before adding it in thin layers, as fleece needs to be fully saturated in order to compost well. As it breaks down, the wool can help the heap to reach temperatures of around 70°C.

The outermost thirty centimetres or so of any compost heap is always likely to be a problem area, due to its exposure to bright light and drying winds. As it dries out, it can also end up acting like a thatched roof, preventing rainwater from getting in, which can then negatively affect what is going on deeper within the heap. The smaller your heap is, the larger its relative surface area will be, and the greater the impact of this dry outer layer. You can lessen the problem by using the hot composting method, incorporating the dried outer layer back into the middle of the heap as the heap is turned. Once you are ready to deconstruct your heap and start using your freshly made compost, check if the outer layer still has some composting to do. If it does, then it's not a bad idea to use this material to form the base of your new heap. Another solution is to cover the top of the heap once you 've finished building it, so as to better compost the difficult outer layer. However, this can reduce airflow within the heap, and it will also have a negative impact on its habitat value for local wildlife. The trade-off for a small increase in efficiency is, therefore, probably not worth it. Instead, you can cover the heap with living plants such as Gourds (Cucurbita spp.). To do this effectively, make a few holes in the top of the heap and fill them with old compost, then leave these planting pockets for a few weeks to settle into the heap before the young Gourds are planted. By covering the heap in living, green material, you protect it from the drying effects of sunlight and wind— and you get the benefit of a bonus harvest at the end of the season.

Compost heaps support a wide range of macro and microfauna and, as a result, tend to be the most biodiverse part of any garden. They are often home to many species of worms, a surprising number of spider species, and usually millions of woodlice. They also provide valuable habitat for grass snakes and slow worms. Once your new heap is up and running, you will very quickly be able to see what you are supporting, while simultaneously providing yourself and your garden with a wonder product that is worth its weight in gold.