Creating an Independent Bog Garden
If you want to create an independent bog garden, simply leave a mound of soil along one edge of your pond.  This should be higher than the planned water level which is usually the same level as the rest of edge.  Take the pond liner over the mound of soil and put it into the wetland area.  If you puncture holes along the sides about halfway down from the top you can ensure good drainage to the top few inches.

Micro Pond Kit
 

You can use one or more perforated pipes run vertically down the side of your bog garden.  Stop it a couple of inches above the bottom of he hole and leave 1 to 2 inches of the pipe above the soil surface.  To ensure that the water leaks out slowly, block the bottom end of the pipe.  This will also keep the drainage holes from getting clogged with dirt.  When you are finished, you can camouflage the exposed piping with plants.

Another option is to use one pipe inside of another.  This will create an even more gradual seepage.  You can use two perforated pipes, one inside the other.  The larger pipe should be at least 10 inches in diameter.  Insert the smaller pipe into the larger, then fill the space in between with gravel.  When you need to water, just place the end of your hose or the spout of your watering can into the inside of the pipe.  The water will then slowly penetrate through the gravel into the soil.  Again, you can camouflage the exposed piping with plants.
                                                                                                                                        
 


You can run a length of rigid perforated pipe horizontally and place it across the bottom of the wetland.  Now, join this pipe to a vertical length of solid (not perforated) PVC pipe with an elbow connector.  If you decide to choose this option, then lay 3 to 4 inches of gravel on top of and around the horizontal pipe to help keep the soil out of the drainage holes.  Remember to block the end of the pipe, and disguise it with plants.

Lastly, you can purchase a leaky flexible hose (soaker hose) from your local garden center.  These hoses are intended for irrigation below the surface and they are less likely to plug up with soil than a regular leaky hose.  Just drape the hose around the bottom of your garden independent bog garden so that it forms almost a complete loop.  Plug the far end and then use a hose to attach the other at the surface.
Park Seed