If the leaves turn yellow or brown and the plant dies while standing up and looking like a tiny yellow plant, it is drying out.
To check the soil for moisture, stick your finger in the top 2 inches of soil and see if it’s damp. If it is, they don’t need watering. However, if it’s dry, you need to water them. In hot dry conditions, water the entire pot so it doesn’t dry out too quickly.
Damping off causes the stem to change color and the plant falls over and dies within a few days. The leaves don’t normally go yellow. Damping off (root rot) is caused by poor drainage and lack of air around the roots. Adding perlite (20-30% by volume) to the soil can increase drainage and aeration around the roots.
There are several ways to increase humidity around plants.
Put buckets of water next to them.
Have pots of potting mix or coconut coir in between the plants. Water these pots (the ones without seeds) every day and as the water evaporates from the pots it will increase the humidity around the young plants.
Put the pot plants in a plastic tray and put that container in a bigger one. Put some water in the bigger container. The plants won’t get wet because they are in the smaller tray, but the humidity will go up.
Put the plants in a large plastic storage container and have the lid partially on.
Put the plants on plastic blocks in a tray and fill the tray with water so it’s just below the bottom of the pots.
Get a plastic fizzy drink bottle (like a Coca Cola bottle). Cut the bottom off it and put it on the pot. You can remove the lid so the humidity doesn’t get too high. As the plant grows, you can increase the bottle size and raise it up off the soil with Lego bricks or something similar. Eventually you remove the bottle altogether.
Get a plastic spray bottle and fill it with water. Spray it on the leaves and around the tent once or twice a day to raise the humidity. This is fine to do in dry climate and when the plants are in a vegetative stage but should not be done during flowering because moisture in the flowers can increase the risk of fungus or mold.
If you are growing in a tent, reducing the airflow through the tent will help to increase the humidity. However, lack of airflow around plants can increase the risk of mold and fungus in the soil and on the plants and flowers.
When the plant is over a month old it should be ok with 20% humidity but it will need watering more often.
Fungus gnats are best treated with a parasitic nematode (available online). The worms eat the gnat larvae and 2 weeks after applying them you have no more gnats. The nematodes work best in warm weather (18C/ 64F) and above.
You can also get Bacteria thuringiensis and spread it on the potting mix and it kills the gnats too. This works in cold or warm conditions.
