One of the most insidious problems that might appear in your marijuana plants is that of root rot. In the case of hydroponic (water) growing, this is an easily detected problem. The roots of the plants will start to turn brown instead of the creamy white color of a healthy root system. Within a short period of time, they will truly rot, causing them to appear slimy. They will also start to emit a strong odor.
Root rot is less evident in marijuana plants that are grown in a soil medium. These plants will start dropping leaves for no apparent reason, and will begin to wither and die. You will also notice the body of the plant dropping and seeming very lifeless. Additionally, you will notice that your plants are just not thirsty when you water them; this usually means that you have watered them too much and the bottom of your pots are standing in water.
Root rot is a very serious condition that can easily lead to the ruination of your entire crop of marijuana. In fact, many growers will not even attempt to treat this problem if a large number of plants are affected. Instead, they will trash the plants and start over. If you are growing on a smaller scale, though, it is usually worth it to try to save the plants. While the rotted roots will not usually recover, a plant that is still strong enough in general will generate a new root system once the issue is addressed.
The very first thing to do is to change the growing environment. If you have a hydroponic medium, be sure to change you water on a weekly basis, flushing the old water out and replacing it with fresh, pH balanced water. This weekly water change will also expose the roots to the air for a short time. Your plants love this, as long as you don’t let the roots dry out.
In a soil-based growing medium, you need to make sure the plant pots do not have standing water in the bottoms of them. If this is the case, you would do well to pull the plant out of the pot, soil and all, and let it be exposed to the air long enough to drain the excess water and dry out some.
After you have removed the waterlogged plants, clean all of your pots very thoroughly with an antibacterial agent to make sure there is no bacteria lingering. Make sure your individual pots have an adequate drainage hole. It often helps to spread a few small pebbles in the bottom of each pot to encourage drainage. Using fresh, dry soil, repot the plants as soon as possible.
Once you have corrected these problems, you should also treat the root system with one of a variety of additives available. The one I have had the most success treating root rot with is Subculture B; it cured the existing root rot in some plants, and prevented it from occurring again. There is also Piranha, Great White, Rooters, and Plant Savers.