I had plants that needed to be kept like that and I killed them. My reason for starting a planted aquarium. I will try to find a humidity gauge.
Here is something I read that may help them grow:
Created by soaking substances in boiled water for several weeks. Substances are: banana peels, potato peels, lettuce, cabbage, spinach, and dried tree leaves in spring water.
Put scalded lettuce leaves in jar, enough to cover the bottom of the jar . Add water that is almost boiling to fill the jar about 3/4 of the way full. Leave this standing, uncovered for 24 hours. Then add about 1oz of old aquarium water and cover the jar. After 1 week days, the water should have growth of infusoria. Every 10 days add a piece of scalded lettuce
Also here is one whom is breeding killifish
and had similar problem