Refilling Raised Beds/disposing of old spoil

[Ucfknight72]

I think this might me a silly question but I’m curious . I have (3) 4’ square raised beds in my backyard. I want to add 3” of fresh mushroom compost to the top to keep them fertile, but this would result in overfilling . I hear you need to add fresh compost twice a year to keep the biological activity going in the beds, does this mean I need to “throw away” the top few inches of soil twice a year? I really don’t have a big yard so I can really dispose of old soil. Wondering what people do

Thanks

 

[Chuck]

I am not new to gardening and I have NEVER heard of having to replace compost.....ever......much less twice a year. All compost is, is organic matter and it never goes away, it just decomposes more and it decomposes because of the microbes in it. It finally becomes soil. Adding mushroom compost is great to use but not for the reasons stated. Just take 3 inches off of the top and scatter it on your lawn or in the flowerbeds. It is still good stuff. Or build another raised bed and put it in there.

 

[DirtMechanic]

Organic matter is basically a stage of carbon. In a soil test it is burned away from a measured mass of soil and when the heated sample is re-weighed, the percentage difference is referred to as organic content on the report. Compost carbon does not go away, it shrinks through a process of oxidation. Obviously a compost pile reduces its volume over time, and this process continues in the earth. Coal is an example of the end of the process if there is enough compost. In our gardens we would not have that much of course, and we add more all along. Its some of the leachable things that are replaced with new compost. Residual humic carbon is not really dissolvable so it stays put and helps by chelating contaminates and holding oxygen and water.

 

[Donatello]

I'd follow Chuck's advice . Remove top 3" and add whatever you want. I use chicken poop as fertilizer, but not too much. Don't want to burn your roots.

 

[Oliver Buckle]

Twice a year is a lot. I top up pots and raised beds when the level drops using some nice compost with a bit of blood fish and bone and some manure mixed in. Gradually, as plants use things up and compost decays down, the level drops, I am doing the flower bed I made in the back garden now, it has been two years and it has dropped about four inches to the bottom of the top row of bricks. Next time I expect it to take a bit longer as there was a lot of compost in what I originally used to fill it.