No water garden is complete without a bog garden as some of the most beautiful and interesting plants thrive in such situations. Many ponds and lakes have a natural perennially damp surround which requires no more attention before introducing plants than to remove unwanted weeds.
If the pond is fed by a natural water supply, it is usually possible to channel the overflow into surrounding land, thus producing an area which is permanently moist without being waterlogged. Alternatively, any low-lying site with a clay subsoil can be periodically flooded over with water to produce a bog garden. During the winter months, rain will supply all the moisture that is required as most bog plants are then dormant.
To make a bog garden on raised ground or where the drainage is very free, creates a different problem which, however, can be overcome with a little effort. Excavate the site to a depth of 38cm (15in) and line the area with poor quality concrete consisting of 12 parts of ballast to 1 part of cement or even weaker, or cover the base with slates, tiles or asbestos sheets slightly overlapping. Another idea is to line the base with a single layer of 500 gauge polythene sheeting perforated in a few places so that it allows water to leak away slowly.
Whatever method is employed, put 6-8cm (23in) of stones or pebbles over the lining to provide adequate drainage. Cover these with a layer of peat tailings or old turves turned upside down. Replace the soil, incorporating liberal quantities of peat, manure or other fibrous material to hold the moisture during times of drought. When finished, the top soil will look like any other herbaceous border, but the roots of the plants will feel the influence of the water, and such conditions shouldRead more on backyardgardener.com