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When and why should you replace the soil in your bog?


Hi! Im Quinton, and I'm addicted to CPs....
I've read numerous times about having to change the soil in bog gardens, and I was wondering why this is and how often it should be done.
Thanks in advance

also when is the best time to replace the soil so that there is minimal effect on the plants?
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Because the peat breaks down over time and becomes bad for the plants. How often you change it out depends on the size and depth of the bog, what you have mixed in with the peat, the water you use and how wet the bog stays, climate, etc., too many variables to be able to give a timeline for when to change it out. If it has been a couple years since the soil was new, dig some of the peat up from the bottom and smell it. If it smells bad, time to change it out. One of my bogs (in-ground) is roughly 5' x 3' with a depth of roughly 18" and goes about 4-5 years before the peat starts breaking down, this is in the Pacific Northwest, where we get lots of rain, relatively mild summers, and winter freezes. It is filled with mostly peat with some perlite and a little bit of sand, and I do not use any kind of mulch on top in winter, which may also affect how fast the media breaks down. Hope this helps.
You start to get clues like the soil seems to have 'slumped' this is due to the decomposition of the peat, consequently it occupies less space. A good test is to dig some out, let it dry a bit and see what it looks and feels like, if it is powdery then the chances are its knackered and needs changing, but the most positive test is from that of your plants, assuming you dont have a build up of salts etc in the soil the plants start top get smaller and less robust each year, you cant miss that as an indicator.

You can, and I do as I am lazy, reinvigorate the bog for a season by digging in pine bark and peat to acidify the substrate, it does work as does top dressing with pine needles, pine bark and or peat, but it is only a short term fix, the proper job still needs to be done.

I do a full repot on my minibogs (all new peat) once every two years.
(they go two full years before being repotted)
because I have observed a noticeable decline in plant growth, height and health if I wait 3 or 4 years..
but 2 years has not been a problem..