The Wetland Garden

The difficulties plants face in chronically wet soils are obvious: excess water and lack of air mean that the great majority won't grow. But, in fact, wetlands can be immensely variable, with a wide range of plant and animal life.

Since a number of plants are well adapted to the rigours of wet conditions, the minimalist asks: why not accept fate and grow what does well? In natural bogs and fens biological productivity and species diversity is low, offering the gardener a good opportunity to enrich the habitat range.

Many wetlands respond well to relatively small interventions. The crucial change is to alter ground levels so that, instead of uniformly waterlogged ground, you have some drained soil and some open water.

At a stroke you have multiplied tenfold the habitat diversity and productive potential of your garden. At the very least, the raising of soil above the water level will allow the growing of mesic plants, without diminishing the contribution of the water's edge and the water itself.

The possible variations of this principle are endless; it has been the basis of many sustainable polyculture systems in the humid tropics, but can he applied anywhere. In these traditional systems, the greatest effects are achieved by simple geometry: the arrangement of raised and lowered levels both in plan and section.

Generally, large open bodies of water are avoided in favour of intricate patterns of small pools, promontories, islands, bunds, and channels. This does not require any greater excavation than a single simple pond, but gives rise to a greater range of microcliniates and the possibilities of radically different treatment in different parts of the system.

These possibilities include the following:

• Siting animal housing partially over a pond to allow droppings to fall in the water directly.
  
• Raising the calcium level in some parts of the system with eggshells, calcified seaweed, or ground limestone.
  
• Pumps for remote fountains can be operated by photovoltaic panels.
  
• Running grey water into a pond system.
  
• Using aquatic animals to convert food waste into useful flesh in place of more usual domestic animals; fish and crustaceans can also eat trapped pests, such as slugs and caterpillars, collected from the garden.
  
• Covering part of a pond system with a greenhouse to provide a warmer microclimate and a source of irrigation water for greenhouse crops. This combines well with a grcy water treatment system.
  
• Providing shade by floating vegetation where overheating is a danger. Alternatives include screens over narrow channels or rafts—either of which can be combined with animal housing. Deep sumps provide refuge for fish, and barrels or undercut caves shelter fish from direct sunilight.
  

Wetland systems are often rich in nutrients because everything runs into them. In fact, they may become too rich, leading to algal blooms, loss of oxygen, and the death of larger organisms in the water. A complete food chain is needed for nutrients to be turned into useful biological material: you must keep harvesting and recycling the nutrients.

Rake out and compost green matter and algae, and from time to time dig out the rich mud in the channels and use it to fertilize the banks. Organisms differ in their preference for enriched or nutrient-poor water, so make parts of the system richer than others.

In a warm, humid climate, moulds present the principal problem for edible crops. To counteract this, create raised dry zones and complement them with good, natural ventilation—encourage breezes by open planting, remove foliage near the ground, and restrict the sheltering effect of nearby trees.