For years I have been growing my Sarracenia in tubs owing to the fact that I moved a lot. Finally I bought a house in Corvallis, Oregon and decided to build my dream bog. I started in April of 2010, and like all good DIY projects, it took way longer than I ever expected. By the time I built the physical structure I decided it was too risky to transplant my plants since they had started their spring growth. I'm a tall guy, and I really like to get a good look at my Sarracenia, so I decided to build an elevated bog. I decided to use concrete retaining wall blocks. We have a local place in Oregon called Willamette Greystone that sells the blocks. The nice thing about these blocks is that you can build curves relatively easily.
Here is a picture of the blocks and the gravel once they were delivered. If you have a big truck you can save money by moving the stuff yourself. Each block is about 8 pounds.
The first step was finding a sunny location to place the bog. I tracked the sun and decided to place the bog in a visible spot that I could see from the dining room.
The second step was to dig down about 8-inches and remove all of the soil and then place about2-inches of 3/4 inch minus gravel as a foundation. If you don't use the gravel all of your blocks will eventually move as the soil shrinks and swells through the seasons. I bought a gravel tamper to pack the gravel and I placed a level on a board to make sure that my foundation was perfectly level. I've seen a lot of crappy retaining wall projects throughout town, and the number one problem I see is that people don't create a level foundation. Also, you should nearly bury your first course of blocks to add strength and stability to the structure.
Note the blocks aren't level yet! Keep working. It's important to get every block level.
laying the foundation and the first course of blocks is by far the slowest part of the project. I probably spent 75% of the time building just the foundation. Once that first layer is in, you just lay the next course by off-setting the blocks. This is called "on bond". This part goes really fast. Eventually though you will find that the wall tapers and the blocks no longer fit properly so I had to cut some of the blocks. This is a royal pain in the butt. Concrete is not easy to cut. You can rent a splitter, which in hind site may have been worth the money. I used a rock chisel, but the resulting cuts are not clean. I then bought a special blade for my circular saw to score the blocks and then break with the rock chisel. To do this right you should just rent the splitter or spend hundreds on a real concrete saw. Another option that would have been easier would have been to make a rectangular bog with no taper. But I was building the dream bog remember. I wanted the curves.
Once all the blocks were in place I decided to back-fill the bog with about a foot of sand. I didn't think my plants needed much more than about 18-inches of soil, so the sand was added to fill in the base. I gently sloped the sand so that water would flow down-hill toward the drain.
I added a layer of weed fabric so all of the sand didn't escape over time and allow the bog to sag.
I then spent about $100 on the pond liner that I purchased on-line at the Pond and Garden Depot
The stuff is expensive. And if I were to do it again, I would design my bog based on the size of pond liner that you can buy, since I wasted a bunch of liner as scrap. There are some important lessons to learn when working with expensive pond liner. First, lay the pond liner in the bog and then fill it up with water. This gives you a realistic impression of how the liner will fit when fully loaded with soil. The reality is, the liner will sag and there will be wrinkles, so if you just measure the dimensions of your bog and cut, without laying the liner and filling with water, you will find that you cut your liner too small. You will curse. You will throw tools. You will need to buy a new liner. You will have a pre-cut liner for your bog annex.
All of the CP text books say poke holes in your liner. I think this is crazy. You want the bog to hold water don't you? Well I decided to install a drain in my bog with a valve that would allow me to open and close the drain. I decided to build the drain by using a bulkhead. This was a new plumbing gadget that I hadn't heard of before. Basically you carefully cut a small hole in the liner and then attach the bulkhead to both sides of the liner. The bulkhead is threaded so it screws together and the liner is pinched in between. The bulkhead has a rubber gasket that should make a water tight seal. you can add sealant glue if you want it to be 100% water tight. I did not. the bulkhead is also threaded to fit pvc pipe fittings, so I added an elbow, two feet of pvc and a valve to control the drainage of the bog.
Here is where I got cheap. The larger the diameter bulk head you purchase, the more expensive it is. Plus, all the parts that attach to the bulk head become more expensive. I think I settled on a 1/2 inch diameter, which, now that it is buried under 18-inch of media and all of my plants, I realize is probably way too small! I placed some greenhouse shade cloth on the top side of the drain to keep the soil from clogging the drain. I then piled some pea-gravel on top of the mesh fabric. My biggest concern was that the drain would either clog or that all of my peat moss would liquefy and escape. Four months later and none of those things has happened, but if someone has a good drain system I would love to see it, since I think it is just a matter of time before this drain clogs. The other regret I have is that I did not build-in an overflow valve / pipe at the surface of the bog. Originally I decided I didn't need one, but now I wish I would have installed a pvc pipe near the soil surface that routed excess water out of the bog. I saw lots of examples on koi pond designs.
I used a 50:50 mix of peat moss and silica sand. more info to follow. It wasn't anything fancy.
After mixing the soil I let it sit in the bog for about a week. This was to allow the soil to settle and compress. If you don't let everything settle, you will put your plants in and then realize everything has sunk a few inches over time. Be patient.
Finally I planted the bog in April of 2011. This spring has been incredibly cold so this picture isn't all that exciting since everything is dormant still. I'll post some photos once everything is up.