Biosphere Terrarium Project/ Growing medium check + Tip sharing

My Alias is B

Nov 3, 2021
Howdy! This is a continuation of a series of threads, if anyone wants background, please check the link (here)

The purpose of this post is to inquire about a growth medium mix I have come up with for the Closed Biosphere ecosystem and if it fits the parameters.

Give the organisms within plenty of room to burrow/grow in
have proper drainage as to not drown the plants
Be rich in nutrients, but not so much so as to kill the plants
provide enough room for growth among the roots
withstand about 70-80% humidity without being overcome by it
have enough material to recycle nutrients to keep the ecosystem thriving.
have about 16 centimeters of depth in the soil, 10 for the organisms, 6 for the plants with the first three being filled with gravel (although, for the life of me it may instead have been 24 inches)

here is what I have come up with to match this problem

33.36 pounds of medium loam
(4 gallons of dirt)
22.0 pounds of peat free compost
(2.5 gallons of it)
5 pounds Gravel/grit
(gives plants plenty of room to hang on, would probably just be enough for the roots of each plant to grow in.)
small amount (8.34 pounds) of topsoil/manure?

Tl;Dr: I am asking if someone could double check me as my math could be bad, and also general knowledge tips on soil mixes that can house arthropods along with a few plants would be nice.

The Snark

Dumpster Fire of the Gods
Old Timer
Aug 8, 2005
the Closed Biosphere ecosystem
Allow me to amend that. A closed biosphere system. The definition is a little loose - vague. It ranges, roughly, from the mold growing in the walls of our bath tub on out to encompassing all life on our entire planet. Don't blink since it changes drastically every fraction of a nanosecond.
Maybe you could narrow the parameters down just a little? A closed self sustaining biosphere needs a time frame as to how long it can exist before evolution and mutations alter it. A balance somewhere between the two absolutes, primal chaos and entropy.
Pardon. Some other thread got my day started with Nietzsche.
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