Rating Manual section 6 part 3: valuation of all property classes

Section 1119: worm farms and farm composting hereditaments

This publication is intended for Valuation Officers. It may contain links to internal resources that are not available through this version.

Assistance in the preparation of this practice note was obtained from technical notes produced by Centre for Alternative Land Use, University of Wales ( www.calu.bangor.ac.uk/) and the worm research centre ( www.wormresearchcentre.co.uk/)

1. The worm farming Industry

To give caseworkers an overview of the industry, the following information has been obtained via the internet from CALU technical notes dated November 2006:-

Calu Technical Notes

Topic: Livestock

Title: Worm Farming

Ref: 040501

Date: November 2006


Worming Farming is divided into two main areas of commercial activity:

  1. production of earthworms for the fishing and composting industry (vermiculture) and,

  2. actual composting of green wastes using worms (vermicomposting)

Both processes are very similar, the main difference is in the quality of feed given to the worms. In the UK, breeding and composting are usually done outdoors in “worm beds”. Vermicomposting is the use of selected earthworm species to assist in the decomposition of organic waste into compost. It is the result of joint action between earthworms and aerobic micro-organisms. Vermicomposting differs from conventional composting in several ways:

Conventional composting Vermicomposting
Waste is treated as one large decomposing mass High temperatures are required (>60ºC) Needs turning to maintain aerobic conditions Regulated by waste management legislation Waste is applied frequently in thin layers Low temperatures need to be maintained (>30ºC) Aeration is done by the natural burrowing action of the worms Legislative position is unclear at present (contact EA)

In several scientific experiments it has been shown that vermicompost increases certain aspects of plant performance e.g. increased vegetable yield and flower production. This is known to occur at certain concentrations of vermicompost substitution, typically 20 – 40% vermicompost, and although plants may be grown in 100% vermicompost they are often of poor quality.


Worm breeders in the UK concentrate on the earthworm Dendrobaena veneta since it can be used by both the fishing and composting market. D. veneta is naturally present in decomposing litter and manures but it is by no means the only “breedable” worm. Vermicomposters in the USA commonly breed and use Eisinia foetida for waste management. However the markets in the UK are geared toward selling D. veneta.

Earthworm Requirements

Setting up a worm bed is relatively easy. The initial bedding material should be a good quality sphagnum peat or the worms’ original bedding material. In the beginning feed and/or compost should be introduced slowly, it will take about 14 days for the worms to become accustomed to new beds / feeding material. After this their maintenance should be straightforward. The bedding material and feed should always be kept moist, low in ammonia and at a neutral pH (5.5 – 7.5 is optimum). Most breeders and vermicomposters cover worm beds with a plastic sheet to encourage the worms to access the upper layers of the feed / waste. The cover also helps maintain a constant temperature.


The products of worm farming are: worms; compost and compost derived products such as compost “tea” and mixtures of vermicompost / peat based compost.

Husbandry and health

Diseases are rare, however, like all animals worms benefit from regular management. Problems usually arise if the basic chemical and physical properties of the bedding become unfavourable. Signs of ill health would typically be: diminishing stock, visible dead worms and a rotting smell. When feeding cereals, be careful of rat infestation.


In the active growing season it is possible to harvest breeding worms for fattening every week. After removal from outdoor beds, the worms are kept indoors at about 20ºC and fed a high nutrient feed in order to increase body weight before selling on. Harvesting of worms has traditionally been done by hand, however some farmers have developed automated methods for separating worms from the bedding. It usually takes up to a year before the initial worm seed crop reproduces sufficiently to produce a harvestable crop.

The harvesting of worm bedding / compost is usually done when worm beds are full. This may take many months, often years, depending on size of the bed, feeding rate and earthworm numbers.


Worms are sold as bait for the fishing industry and for composting organic wastes. Compost and compost derived products resulting from vermiculture may be sold to gardeners and horticulturalists. However, composts resulting from waste treatment may not be sold without a licence; however the compost may be used on site in unlicensed premises. Waste management legislation is constantly changing at present and each individual producer will need clarification on his / her particular circumstances before proceeding.


Worm breeders are not required to be licensed but are governed by usual agricultural regulations. However, anyone considering using worms to compost waste should contact the Environment Agency (EA). Waste treatment might require a Waste Management License although composting very small amounts is exempted but this also needs to be approved by the EA.

Setup Costs and Returns

The primary cost in worm breeding lies in the initial set up, following on costs other than in feeding material is low.

1,000m² Worm bed (inc. construction) Worms (500kg) Bedding £10,000 £3,000 May be sourced from paper mills and farms

Wormbreeders can expect to earn up to £800 per 300m² bed per month from selling worms. Vermicompost is sold at around 80p per litre; vermicomposters composting green wastes are paid around £25 per tonne “gate fee” by the local authority for diverting waste from landfill.

Sources of Further Information





End of CALU notes

2. Rating of worm farm and farm composting hereditaments

2.1 Non-exempt non domestic land and buildings

Worm farming and commercial composting does not qualify for agricultural exemption as the land so used is not arable or pasture and any buildings so used will not be considered ancillary to agricultural land. Worms do not qualify as livestock kept for the production of food or wool. If the worms are bred on an agricultural unit, then unless the worms are wholly used on the farm for agricultural purposes e.g. for soil improvement or producing compost for the farm itself from material within the farm, then there will be a composite, part exempt hereditament.

As far as rating is concerned the recycling of green waste for compost is in a similar category of process to that of worm farming, as the CALU notes illustrate, which may or may not involve worm activity as part of the process (whether it does or not is not particularly relevant to rating). Where waste is brought onto a farm hereditament for processing, a payment will be made and the farm will become partly a waste management hereditament. Green waste will be transported onto the site, and sorted and shredded before laying in windrows, which are turned as required. After approximately six weeks the compost is sufficiently decayed to be spread on the land. Such hereditaments often have contracts with Councils, and an example of the scale of contracts is where a farm might process 7000 tonnes at a range between £15 and £20 per tonnne as at 2006 prices. Such commercial processing is not considered to be an agricultural process until the point where the compost is ready for spreading on the land.

2.2 Valuation approach

A rentals method should be adopted based on the rental value of any former agricultural land uplifted as necessary by the added value of a planning permission if any and any rateable plant in the nature of a structure. Added to this will be an amortised sum to reflect the value of any rateable structures comprising the worm bed.

2.2.1 (i) Where situated on an agricultural holding as a farm diversification

The hereditament will be the whole holding and strictly the value of rateable buildings should be apportioned out of the whole. Thus, the worm farm operation should not be viewed in isolation from the farm hereditament out of which its value is being apportioned. Thus it is not envisaged that any uplift in value should be made to reflect, for example, small size, low overheads and higher than average profit for that particular ‘crop’. The resulting entry will be a composite described as part exempt.

2.2.2 Open air beds:

The area of land used together with access paths and will lose its exempt status. The worm beds usually comprise low areas of composting material on the surface of the ground covered with polythene sheeting, enclosed by vertical treated timber shuttering boards and pegs. The timber enclosures will be no higher than approximately 20-30 cm high. CALU technical notes suggest set up costs including construction for a 1000m2 worm beds at £10,000. The enclosing structure is of low cost and easy to construct, well within the capability of a practical farmer, and it is unlikely that such a structure in itself would add significantly to the rental value of the land. As the boards are simply akin to scaffold boards pegged to the ground it is doubtful whether they are rateable. The worm research centre states that “there are at least six companies engaged in selling and setting up large-scale outdoor worm composting (or worm farming) systems in the UK. The typical size of modular units sold is 1,000 m2 and each costs around £15,000 to buy and install. Larger units have also been commissioned (10,000 m2) and these would be comparable in waste processing capacity to many medium sized municipal composting-facilities”.

In order to avoid the argument as to whether such structures are rateable or not it is suggested that the rental value of the land set aside for this use be uplifted by no more than 25% to reflect the non agricultural use and any planning permission.

2.2.3 Concrete base and retaining walls:

Sometimes there will be concrete bases and perhaps a number of circular sewer pipes resting thereon that form the basic structure. Where there are the more substantial structures used to form the worm beds and the cost is clearly significant, and not be able to be reasonably reflected in the land value, it will be necessary to undertake an amortisation of cost. This annual equivalent rental value addition must be added back to the estimated rental value of the land as at AVD. Any roads specifically constructed to service the non exempt parts of the farm should be included in the costings.

It is suggested that the costs of the concrete structures taken over a 15 year payback period at an amortisation rate of 6% to arrive at a rental value addition. On this basis a £10,000 investment will be equivalent to £1030 rent and £20,000 equates to £2060 rental equivalent.

When adjusting costs of rateable plant, only the fixed plant that forms part of the hereditament will be in view, not the costs for worms or bedding or any other ancillary element.

2.2.4 Use of former farm buildings:

The buildings will lose their exempt status. In rural areas, however, it is suggested that the rental value of such a building would be limited to those in the agricultural market. The mode of category of use would still be of an agricultural nature in planning terms. It is considered that a permission specifically for worm farming and a use according therewith would still be in the mode or category of agriculture, though not exempt for rating purposes. Clearly if any non-agricultural planning permission has been obtained which would serve to open the market up to a wider range of bidders, this should be reflected in the bid a vermiculturalist would have to make in a competitive market. The nature of the building, its location and letting potential in its existing state will have to be judged. It is not envisaged that values would, for example, be near comparable with industrial or warehousing in the locality. If an otherwise redundant agricultural building is used, with no further planning permission, its limited value should be taken into account.

Any comparable evidence of lettings of former agricultural buildings for storage or non agricultural uses will be useful. If no special permission has been sought or is not required then the value would probably not exceed an agricultural bid.

2.2.5 (ii) Where the worm farm or compost hereditament is occupied as a separate business.

The same principles will apply in valuation approach except that the hereditament will not be a composite or described as part exempt. It is not envisaged that particular problems will be encountered where worms are bred in industrial type buildings in areas where a competing market for such buildings exists.

2.3 Cost information

Where cost information is available this should be recorded and analysed to apply to the rateable parts of the worm culture process. i.e. any significant enclosing works in the nature of a structure.

2.4 Liaison with mineral valuer

It should be noted that the MV has specific responsibilities for all composting and waste management hereditaments, and the MV should be contacted where any composting operation is carried out on a farm hereditament and any waste management operation is identified using worms or not, and the matter passed from the group to MV responsibility. The location of MV offices will be found on the following link.


2.5 Advice

Assistance and advice can be obtained from the Regional Building Surveyor as necessary, and from CEO Technical Advisers. Cost details available and any analysis carried out should be submitted to CEO through the TA’s.