I added 3 bottles producing CO2 for the plants in the closet which seems to be a good idea. What I did was putting a couple hundred grams of sugar in each bottle, alittle urine (yup piss alittle filling bottom of the bottle) and then added some yeast and finally warm water up to around 70% of the bottle's total volume. A small hole was drilled into the cap using a knife (about needle sized hole, so you can use a needle). Then cap was screwed back on top, the bottles shaken violently for a while (hold yer thumb on the hole!) before putting them into the closet around with the plants. This produces CO2 gas which will be going on for couple weeks during the fermentation process. Extra Co2 seems to be beneficial for the plants, and I also spray them gently with carbonated water ("club soda" or "seltzer water" is what its called in english I think) with low sodium level in it.

Doing the above will make the solution fizzle and bubble and foam thus only filling about 70% of the bottle so it doesnt bubble over, and it also builds pressure so don't shake the bottle before making the hole in the cap or it might explode in yer face. The point of the small hole is to gently release the pressure and thus let Co2-gas flow out to the plants within the closet they are all placed.

Each bottle used is a 2.5-litre Coca Cola plastic bottle.