Composting
Severn Waste Services has been composting green garden waste since the early 1990’s. The resultant product is a composted soil conditioner marketed under the brand name ‘Greengrow®’.
Every year thousands of tonnes of Greengrow are supplied to a wide range of customers - from the general public, to landscape gardeners and contractors, farmers and commercial growers, stately homes and gardens, local authorities and engineering companies.
The following sections explain:
- Why it is important to compost.
- How we compost green waste
- Properties of ‘Greengrow’
- Uses and applications of composted green waste soil conditioner.
- More useful information.
Why compost?
Some 60% of all waste generated by households in the UK can be composted. Composting organic materials like green garden waste and vegetable peelings makes a substantial contribution towards diverting waste from landfill, and avoiding the potential for environmental pollution.
Composting is seen as a key component in local and central governments’ drives towards more sustainable waste management.
In addition to the waste management benefit, there is the ‘win-win’ effect of having a valuable product at the end of the process, as a reward for our efforts. Using composted materials in the garden improves soil fertility without the use of chemical or peat-based products, and really ‘closes the loop’ in recycling our waste into new plants.
Of course, we encourage people to compost their own kitchen and garden waste at home and there is plenty of help and information around to tell people how to do it. For useful links, see end of this page.
However, for people with larger gardens or only limited capacity for home composting, we provide a service to deal with big volumes green waste.
How is it made?
Composting is a natural biological process in which micro-organisms present in organic waste break it down into a stable organic material that can be easily stored, handled and spread on land. Any harmful micro-organisms or weed seeds that may be present are killed by heat generated during the composting process (nominally around 60oC) [INSERT process picture]
At our Hill and Moor composting site near Pershore we receive over 20,000 tonnes of green garden waste per year. Most of this comes from our household waste sites in Worcestershire and Herefordshire, where householders have placed their garden waste into our green waste containers (hopefully without the plastic bags or any other ‘contaminating’ material!).
At Hill and Moor we shred the waste and place it into long piles called ‘windrows.’ Then we just let nature do its stuff. We monitor the temperature and moisture content in the windrows, and we irrigate and turn them over regularly to provide good oxygen supply and to maintain the correct conditions for uniform decomposition.
(For more information on the science of composting please visit The Composting Association)
After about 14 weeks the composted material is screened using a rotating drum sieve. Most of our product is supplied at less than 10mm although we can provide coarser material at less than 25mm. Screening removes any ‘woody’ material that can be re-introduced into the windrows. It also removes any bits of plastic or other contrary material that has escaped the eagle eye of our operatives.
Properties of Greengrow
We call our composted product a soil conditioner rather than a compost, so as not to confuse it with branded growing media – mainly peat-based - that you see in garden centres.
Greengrow improves soil fertility; releases plant nutrients slowly and encourages vigorous plant root systems.
It is a good source of essential trace elements and supports the activity of soil micro-organisms that convert soil nutrients into forms available to plants.
Applications of composted green waste soil conditioner improve soil structure and its ability to hold water.
Laboratory studies have shown that it can give effective control of economically important crop diseases, such as club root on brassicas, white rot on onions, stem canker and black scurf on potatoes.
Typical properties of a composted green waste soil conditioner are shown below. For sources of further information see links below.
Properties of typical composted green waste soil conditioner
Nutrients |
(Total nutrient kg per tonne of moist compost based on typical analysis)
|
|||
Nitrogen |
Phosphate |
Potash |
Magnesium |
Sulphur |
as N |
as P2O5 |
as K2O |
as Mg |
as S |
8.1 |
3.3 |
6.6 |
2 |
1 |
Potentially Toxic Elements - (Typical values compared with the Composting Association Standard for Composts) |
||||||||
Element
|
Cadmium
|
Chromium
|
Copper
|
Lead
|
Mercury |
Nickel |
Zinc |
Units |
Typical
|
0.71
|
19
|
45
|
108
|
0.17 |
18 |
186 |
mg per kg |
Standard
|
1.5
|
100
|
200
|
150
|
1 |
50 |
400 |
dry matter |
Other parameters
pH - Around 8.5 (Measures acidity)Electrical conductivity - Around 770 mS /cm (Measures concentration of soluble salts)
Bulk Density - About 0.6 kg/litre or 1.6m3 per tonne
Loss on Ignition - About 20% (Measures organic matter content)
Carbon: Nitrogen (C:N) ratio - About 12
A good quality composted green waste soil conditioner will contain the odd piece of glass, plastic or other contaminants. These are likely to amount to less than 0.2% by weight in total.
The composting process should eliminate all weed seeds (measured as Viable Seeds or vs per litre). A count of 1 or 2 vs per litre is considered acceptable.
The availability of nitrogen in the product is relatively low compared to say animal manure, but this is important in areas of the country where groundwater is susceptible to infiltration of excessive nitrate (Nitrate Vulnerable Zones as expressed by the Environment Agency).
Applications and availability
We provide Greengrow to a wide range of customers and for a variety of uses.
It is most commonly available to the public in 40 litre bags (about 25kg) at many of our household waste sites – for £2 per bag. We can also supply larger quantities in bulk – either collected by the customer from Hill and Moor, or we can arrange a delivery. We charge £2.50 per tonne plus VAT for bulk product, with delivery charge on top. Delivery charges depend on where you are, what quantity is required and what access is like to the delivery point (in relation to vehicle size). For a quotation call 01386 443376.
Greengrow can be used as a general soil conditioner – working 25-40 mm into the top 150 mm of topsoil. A more generous application to the surface will act as a mulch.
We have supplied Greengrow for a host of users and applications, like:
- Improving the soil in municipal parks planting beds.
- Adding to the (barest of) topsoil on new housing developments.
- Providing a substrate for potted Christmas trees.
- Landscaping and tree planting on new highway developments.
- Soil conditioning for turf growers.
- Soil conditioning for allotment holders and commercial growers.
- Soil conditioning for farmers and particularly organic growers.
- Improving the planting beds in the gardens of stately homes and other tourist attractions (Coughton Court and Studley Castle near Redditch, Sudeley Castle near Winchcombe, Hampton Court, near Leominster).
- Substrate preparation for new sports fields.
- Remediation of contaminated land
- Growing media in earth retaining structures.
More Useful Information
For all users of Greengrow composted green waste soil conditioner, please note the following HYGIENE ADVICE:
- Wear gloves when handling compost or soil.
- Always wash your hands using soap and water prior to eating, drinking or smoking.
- Wash and disinfect any cuts or abrasions to the skin immediately.
- Cover them with a waterproof dressing.
There is a lot of ongoing development work and field trials demonstrating the advantages of using composted green waste soil conditioners. See links below.
The Composting Association - www.compost.org.uk
The Waste and Resources Action Programme (WRAP) - www.wrap.org.uk