Depth of Raised Bed

Hi Everyone,

We are building our first FarmBot on the roof of our University building in Belfast, Northern Ireland. It’s possible that we may have a weight limit per sq meter imposed on us by the structural engineers. I’m trying to workout two things:

  1. The weight per sq m that a standard FarmBot would exert on our roof if we build the raised bed to the specs ( which is 350 deep, filled to the brim with rich, soft soil and compost?

  2. If we have to reduce the load on the roof, can we simply reduce the depth of our raised bed to 200mm (as an example) instead of 350mm?

Thanks for taking the time to consider the above and help us out.



Hey @neildaanderson I had the same questions to answer!

I built a mobile raised bed in 1,5 m x 1,5 m with a “soil” depth of 42 cm. I found values around 1300 kg /m^3 for moist soil which then really fast turns into more than a ton of weight. I placed my bed outside and wanted to use natures´rain as a water source too. Therefore I built in a drainage level with swelling clay and a little bit of an angle that water can drain from the bed. I guess looking back that was a good decision, otherwise the bed would have been flooded at some point.

About the infill of the bed, I was unsure too. I guess if you do not want to use fertilizer you need to have a great depth (>= 1m?) to be able to use compost an other layers as fertilizer through the years. I used a coarse material above the swelling clay. I will see during this season and the next seasons how it behaves, but I am using fertilizer as well. Maybe some people with more bio background can add some words…

Hope I could answer some of your questions…