Here's a cheap way to get greenery that's the right colour as in nature , florists sell dried moss for flower arranging,
not the type of sphagnum that you use for hanging baskets ( altho it might also work) but the stuff that grows round tree bases & on old logs etc. it will have been heat treated to kill bugs, Hobbies stores sell it in small bags at £2.50 but you don't need to spend any money if you can collect your own.
Collect the sort of moss you see on the woodland floor & peel it up into a bag, shaking off any obvious woodlice etc.
Take it home & microwave it, it needs a bit of experimenting to see how long it takes to heat it up enough to kill any bugs, then get your electric blender ( if it's not yours then ask permission
)& use it to shred it into tiny bits, you can end up with a bucket full at no cost & like all dried plants it will last for donkeys years. As an ex pro model maker I used this quite a lot, now retired I'm using it right now on something I'm currently working on.
Use PVA glue to coat up the section you are doing, as your scale is 1/72 then you might need to put your shreddings into a kitchen sieve & swirl it around with your fingers so the finer stuff goes through, If your diorama is already in situ then you won't need to worry if it's not stuck properly.