Carnivorous Plants/In ground bog garden
QUESTION: I just dug out a 4x8 foot bog in my backyard that is 2 feet deep, and i am not able to find my dvd on bog garden specifics. My quesion is this. after line the bottom with sand, and install the plastic tarping, how high up should i make my drainage holes? I am going to put about 2 inches of sand inside the plastic liner, do i make the drainage holes at that line? higher/lower?
ANSWER: There are two schools of thought on this one. The first is to make the holes a few inches from the bottom to create a reservoir. The second is to make the holes on the bottom in one section of the bog only. This allows water to flow in a specific direction, but still retain some water.
Making the holes on the sides is perfectly fine if your underground water level doesn't rise above where you make your holes. If you happen to have heavy rains and your water level rises above the level of the holes, you risk introducing soil contaminants. Even if you flushed the soil, contaminants would remain in the reservoir.
Most people simply make holes on the bottom, either in one section only (my preference) or throughout the bottom, spaced about 12 inches apart. Having holes on the bottom allows you to flush the soil if contaminants enter the bog.
Our bathtub garden is ideal because it has a drain hole on one side only. We place flytraps closer to the drainage because they prefer more aeration than Sarracenia and sundews.
If your intent is to create a reservoir, you can place the holes 4-6 inches from the bottom. This would allow enough clearance if contaminants entered through the holes, but still keep your soil moist. I'm not sure how you're going to water, but if you added water in the center of the garden, that will create a flow of water to the edges, which will help reduce contamination.
Take photos of your process. I'll be glad to post an album of your bog garden in our photo gallery.
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QUESTION: I was planning on just using a peat miss/perlite mix... But it sounds like I should include silica sand as well? What type or ratio would u recommend for the South Dakota temperatures? I was going to use pebbles or sand to line the bottom/inside of my plastic tarping also. Or increase my perlite ratio towards the bottom of the bog. Am I on the right thought process? Thank you again for answering these questions
You definitely want good drainage to avoid the bog being completely filled with water, especially during a heavy downpour. (This is why we can't have in-ground bog gardens at our nursery. The water table would rise to several inches from the soil surface in winter.)
In rereading my previous response, I realized I was unclear about something. Wherever you place your drain holes, whether on the bottom or sides, it needs to be below the level of the sand. If you place it on the sides, then you'll need to have the sand go above the holes at least a couple inches, more if possible because of compaction over time. The intent is to make sure that the holes won't get plugged by peat or perlite. Sand is a good material for the bottom layer, as is pea gravel or small pebbles, though silica sand is cheaper.
For your mix, if you trust the drain holes to function properly, equal parts peat and perlite would be fine. This will be much easier to work with. Otherwise, you can substitute sand with perlite. Finally, top dress your garden with long-fiber sphagnum, live sphagnum, or decorative pea gravel. This will prevent soil erosion when you water your garden.