It doesn't have to be large but it should be at least one metre in depth. Also, digging out lawn space is preferable as it's under-utilised space and the turf is handy for lining the bog. Keep the turf that you dig up.;
, Once you've dug the hole, use black plastic pond liner to line it. Poke a few holes in the liner here and there.
 Shovel over a layer of gravel and pebbles. Make this layer about 8 centimeter (3.1 in) high. Cover this with a layer of peat.
 If you used a different part of the garden, place those pieces back into the bog.
 Using decomposed plant matter, peat, fibrous plant material, and soil, fill the bog garden in.
 Plants that might be ideal for your bog garden include:

Hostas






Bog primula (they need shade)






Irises






Marsh marigold (Caltha palustris)






Forget-me-nots






Polygonum






Crocosmias






Monardas (wild bergamot)






Some ferns.
 The moisture content will be retained much longer.
 Do this regularly.
 Like any garden, weeds will grow and they need to be removed on a regular basis. Sedges can become a problem, as can buttercups, which will grow like weeds. Japanese iris will also grow like a weed.
Dig out the area for your bog garden.
Line the bog area.
Line the liner.
If you cut the bog space out of the lawn, place the pieces of turf back into the bog, facing upside down.
Fill the hole.
Plant with suitable bog plants.
Keep watered using a hose.
Fertilise with a liquid fertiliser.
Weed regularly.
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