Frequently asked questions
■ What plants grow best on wet land?
THERE are important distinctions between plants that enjoy moisture and those happy to grow in bogs and marshes. As stated in Water Gardening by Perry D. Slocum and Peter Robinson, ‘Bog plants and marginal plants, unlike moistureloving plants, thrive in totally saturated or submerged soils, a condition that would cause the extensive range of moisturelovers to quickly succumb’. A good example would be sneezeworts or heleniums – herbaceous perennials that need moisture, yet would turn up their toes in waterlogged conditions. The bog and marginal plants suited to wetter places with low soil oxygen include some that are potentially invasive and should not be planted close to natural waterways. American skunk cabbage is banned from sale in the UK and our native flowering rush (Butomus umbellatus) has been banned for sale in many American states.
■ How do I make a bog garden? BOG gardens are often constructed alongside a wildlife pond by finishing the edge of the pond but then creating an adjacent basin, lined but with holes made in the base to allow water to slowly seep out and avoid stagnation. A layer of pebbles is placed over the liner, fibrous loam added and a means of irrigation installed such as a perforated pipe. For a stand-alone bog garden, place a liner in a dug-out hollow and make one hole per square metre. Cover the base with gravel, introduce a perforated pipe perhaps attached to a cistern and cover this with more gravel before filling in with soil and plants.
■ Why can’t all plants grow in wet soils? ALTHOUGH an abundance of water sounds life-giving, plants can have too much of it. Roots need to breathe and when water fills soil air pockets for long periods, this can be a problem. Roots cannot function normally, leading to chlorosis (pale growth), rotting and death. Plants evolved to grow in moist soils often have aerenchyma, a spongy tissue forming air spaces between cells in roots, leaves and stems to help with oxygenation and sometimes buoyancy. Others make fine surface roots to scavenge oxygen from the soil surface. Swamp cypresses produce ‘knees’ or roots that project from the ground like snorkels.