Structure
A seating platform/cubicle should be constructed at least 1 metre over were the compost heap will be. How you make the platform is up to you. The design will be dependent on the materials and budget available. Ensure that there will be a through flow of air below the platform - a boxed in pile with no ventilation may well go anaerobic and start to pong. Its sensible that the compost heap should fenced off in some way to prevent badgers or rats etc from eating the contents! Fencing may also be required to prevent deer or livestock from eating willows and other planted species.
Siting
The treebog must be sited where the surrounding willow and other planted species will have plenty of sunlight otherwise photosynthesis will be limited and the plants will not thrive. To keep the Environment Agency happy treebogs should be situated over 10m from watercourses or springs and away from areas liable to flooding.
Willow planting
The best time to plant the willow for a treebog is between October and March, as then the willow has a chance to get established before the on set of summer. However it is possible to construct and use the treebog structure at any time and then plant it out at the appropriate time of year.
If unrooted willow sets are used they should be of a vigorous variety, and if they are planted out after the middle of April they should be well mulched and watered everyday for the first month or they will not take (i.e. the roots will not develop and they will wither away).
Named osier or biomass willows are recommended since these will grow vigorously and can tolerate annual coppicing. Such varieties are also suited for use in basketry and hurdle making. If you are gathering local wild osier or other willow to plant your treebog, use willow that has been coppiced or pollarded recently, because young wood makes the best cuttings. Avoid goat willows, which although vigorous growers, do not respond well to annual coppicing and can be a bit lightweight for working with.
Willow management
The willow can be coppiced annually or left longer. You will however find that it will grow quite large! Cut the willow between November and early March and don't be afraid to cut it right down to the ground or the top of your living woven willow hurdle - as long as it is not smothered with weeds and has sufficient sunlight it will re-grow vigorously using the nutrients and moisture provided by the treebog.
Inputs
Sawdust is useful to aid the correct carbon-nitrogen ratio. But beware if your toilet is used by visitors, sometimes known to fill an entire treebog with sawdust (or straw) in just a few days in their attempts to hide every trace of the poo! Use untreated sawdust only in small quantities, or add a daily or weekly layer to the compost pile. Wood ash is helpful in keeping the compost pile sweet. However, make sure all the embers have gone out and the ash is cold or you may end up with a treebonfire!
In some situtations it may be worth separating inputs if a disproportionate quantity of urine is entering your treebog. Composting wee and poo separately would be a solution - e.g. a separate treebog or a simple straw pissoir, for pee only. Separation of solids and liquids prevents the compost pile from becoming too wet and going anaerobic and causing smells.
Official Requirements
If your treebog is a temporary structure and has no permanent foundations, planning regulations do not apply. Environmental Health Officers will have no objections as long as access to the compost pile is restricted from children and pets (chicken wire or similar barrier) and hand washing facilities are provided nearby.
Environmental health regulations for composting toilets come into force only with regard to the secondary handling of the compost pile. There is no secondary handling using a treebog and so it is exempt from these regulations.
See also: Treebogs (General info)
and: Toilets and the shit problem
