Hi Maria,
I haven't a bog quite that large but at 12 X 4-5 feet it comes
close. You don't want to really make it much wider, since you'll
find it rather difficult to plant things farther out than you can
reach... I found that out with my first bog which used to be about
6-7 feet wide. Now, I have two bogs at about the dimensions I
mentioned above. Anyway, with some help, I dug the hole in the
first bog down about 1.5 to 2 feet deep. The second is between
2.5 and three feet deep. Two reasons the second is deeper: 1) my
helper was feeling very frisky and 2) It is in a sunner location
which losses water much faster. The deeper you dig the more
water that is stored underground. I have not watered either bog
once this year! And only once the year before, and that was
during a drought in the late summer.
As for construction, I used heavy duty UV resistant black
plastic to line the holes. I'm not sure of the mil. of the plastic
but it's around 4-6 or so. I used two layers of it and bought it
from Channel (which doesn't exist anymore) but have seen the same
stuff at Home Depot. First I put down a layer of sand, then the
plastic, then another layer of sand... I don't know if the sand
does much but it made me feel better ;) I tucked the edges of the
plastic under some patio blocks which form a walk around the bogs.
I've have some trouble with the soil falling, right at the edge of
the hole. This can cause the patio blocks to lean inward. It's
rather annoying (and if soil settles while you're standing above
it, can pitcher right into the bog!!! Remember Tom??) but I managed
to fix it, through patient settling of the soil and getting the soil
inside the bog to support the soil on the outside of the plastic.
I suppose a wooden frame right around the top to attach the
plastic to will also help but I avoided wood so all parts of the
construction should remain viable for many years, maybe even decades.
Soil: 100% peat in the bottom, the top half foot is 1:1 sand peat.
Some parts are overgrown with Sphagnum moss, which is over six
inches deep in some parts. The adult S.leucophylla seem to like it
but it can be a weed for the smaller plants like Drosera, Dioneae and
Pinguicula. Over time, more peat has been added because of settling
and decomposition of the older peat. Now that the Sphagnum is so well
established, all I do is through down a layer of sand on it, not
quite burying it, but matting it down. This slows it some and should
be creating new soil as the moss beneath breaks down with the sand
already mixed into it.
Dave Evans