Who knew composting was so complicated – and that there was even science behind it?
In theory all it involves is taking a pile of organic matter, be it kitchen waste, garden waste, and anything else appropriate you can find, and letting it all rot down over time.
Yet many gardeners will understand that the quality of the final product can vary, so it’s important to get the right mix and conditions.
All this coming week, as part of the NI Science Festival, Hillsborough Castle & Gardens is hosting a series of workshops where you’ll learn all you need to know about creating the perfect homemade compost.
According to head gardener Claire Woods, compost is “any plant growing media made from broken down organic materials”.
Commercial compost differs from the homemade variety both in its composition and the fact that it often enhanced with added fertiliser.
As for the homemade stuff, if done correctly, it’ll be rich in plant nutrients and beneficial organisms.
At Hillsborough Castle & Gardens, Claire says, they compost all green waste, except perennial weeds like bindweed and diseased material, along with brown waste in the form of cardboard from packaging and shredded paper from the offices.
The finished product is applied in variety of ways, including for potting plants, filling containers, adding to the soil as a conditioner and applying to the soil surface as a mulch.
“We add compost to improve the fertility and structure of the soil, which in turn increases air flow and aids water retention,” she says.
“It also stabilises the pH of the soil around the optimum is 6.5 - the figure which denotes the acidity or alkalinity of a solution - as well as supporting lots of the essential bacteria that already live in the soil and adding many more bacteria, fungi and other soil micro-organisms.”
The science of composting arguably comes into play when seeking to get the correct C:N (carbon to nitrogen) ratio, which enables the micro-organisms to break down the material more efficiently.
“The carbon in the form of sticks, card and other brown materials provides energy and nitrogen from soft green material is used for protein production,” says Claire.
“Too much carbon – the ‘brown’ compost materials such as chopped sticks, straw and cardboard – the decomposition will be very slow, as it doesn’t break down quickly enough and the heap stays cold.”
She also cautions against using beech, pine and oak leaves, all of which have high levels of tannins, something the micro-organisms don’t care for.
You can also over do it with ‘green’ material.
“Too much nitrogen, such as your grass clippings, causes the compost to become smelly, soggy and very unpleasant,” says Claire.
“If this happens try adding some shredded cardboard or paper – the balance we are aiming for is around 25- 30 carbon to one nitrogen.”
In terms of materials to avoid, the Hillsborough head gardener suggests steering clear of diseased plants, perennial weeds (dandelions, perennial nettles or creeping buttercups), meat, fish, dairy, cooked food, cat or dog litter.
“If you are not careful about what you put into your compost you may introduce weeds and disease,” she says.
Otherwise, it’s anything goes, including grass clippings, soft prunings, fruit and veg peelings, cut flowers, and coffee grounds for nitrogen
Also add plenty shredded cardboard, straw, chopped harder prunings and shredded sticks for carbon.
A Beginner’s Guide to the Science of Compost runs daily at Hillsborough Castle & Gardens until February 21. More information at nisciencefestival.com/events/a-beginners-guide-to-the-science-of-compost-4
