How compost can help your garden flourish
Insight and tips from an expert gardener at Hillsborough Castle
Date: 27 September 2024
Author: Claire Woods
Our world-famous gardens take a lot to maintain and grow throughout the year, and composting is one element of this. Compost refers to plant-growing media made from broken-down organic materials, such as food and garden waste.
It is rich in plant nutrients and beneficial organisms, and this sustainable method helps our 100-acre castle grounds to flourish and grow.
We compost all our green waste except perennial weeds, like bindweed and diseased material, along with brown waste in the form of cardboard from packaging.
Gardens manager Claire Woods explores how compost is used in the gardens at Hillsborough Castle, plus expert advice on how to use it to improve the health of your garden at home.
Why do we use compost?
We add compost to improve the fertility and structure of the soil, which increases air flow and aids water retention. It also stabilizes the pH of the soil: the pH denotes the acidity or alkalinity of a solution and the ideal for soil is 6.5. Additionally, compost supports many essential bacteria that exist and live in the soil, adding even more bacteria, fungi and other soil micro-organisms.
These micro-organisms break down the organic matter and allow the plant to use the nutrients released, thus promoting healthy growth effectively. As a result, this can also reduce soil borne diseases.
By adding compost, you can increase the organic matter in the soil. If the soil texture is heavy and clay-like, compost will lighten it; if the soil is sandy and free-draining, it will help to retain moisture.
Compost also encourages earthworms and, if you’re putting it on top of your soil, it will reduce erosion. Once we clear beds, we apply a thick layer of compost which helps control weeds and insulates the soil over winter.
A chipper machine, which is used to shred material to make compost. © Historic Royal Palaces
Preparing compost for Hillsborough’s gardens
At Hillsborough Castle, when preparing to make our compost, we shred or chip all our shrubby prunings and add it to the compost bays along with soft green nitrogen, building it up quite quickly. Adding a lot of material at once starts the heating process.
The pile heats for two to three weeks, essentially cooking up our compost. The micro-organisms get to work, using carbon for energy and nitrogen to produce protein, and then cool off. We then use a telehandler to turn the whole pile, but at home you would move it from one compost pile to another, which gets the heating process going again, allowing oxygen in.
We turn ours every four to six weeks. If you get the balance just right, you will produce compost in two to four months and it should always have a nice, earthy smell. If your pile is carbon-heavy, it can take up to a year.
A compost bay in Hillsborough Castle's gardens. © Historic Royal Palaces
How to make your own compost
When making compost, it is important to get the carbon to nitrogen ratio C:N right, as well as the air and water percentages, because the microorganisms involved need balance. Carbon, in the form of sticks, straw, cardboard and other brown materials, provides energy while nitrogen, from soft green material, is used for protein production.
However, introducing too much carbon slows down decomposition, which means it won’t break down quickly enough and the heap will stay cold. Using the wrong type of carbon can also cause the same issue. Beech, pine and oak leaves contain high levels of tannins (a bitter chemical compound), which micro-organisms dislike.
Too much nitrogen, such as your grass clippings, causes the compost to become smelly, soggy and very unpleasant! The balance you should aim for is around 25- 30 carbon to 1 nitrogen.
Dos and Don'ts of Composting
Dos
- Do add grass clippings, soft prunings, annual plants, fruit and veg peelings, cut flowers, tea bags and coffee grounds for nitrogen
- Do add shredded cardboard or sticks, straw, or chopped harder prunings for carbon
- Do make a bigger pile if you are finding it hard to heat
- Do turn your pile regularly, as this will help ensure you reach the optimum oxygen concentration of over 10%.
Don'ts
- Don’t forget to consider the particle size of your carbon products - the finer you shred the material, the faster the process will be
- Don’t add diseased plants, perennial weeds (dandelions, perennial nettles or creeping buttercups), meat, fish, dairy, cooked food, cat or dog litter to your pile!
- Don’t add too much newspaper – stick to a small amount and shred the paper thoroughly. Newspaper has a carbon to nitrogen ratio of 560:1, so it must be shredded and balanced out with a lot of high nitrogen material or the process will be delayed.
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