Over watering is one of the biggest mistakes new growers make, reason for this is, because they feel the need to give there plant everything and will overdue a lot of things and one of them is over watering. By over watering your plant you soak the roots so much, they can’t get enough oxygen and slowly die. The plant shows signs of over watering by: Wilting, droopy look, yellow and or dead leaves falling off, which includes leaves that don’t look dead falling off. One of the best ways to tell how NOT to over water is by, picking up the pot when it is dry and then picking up the pot after you water. (This is a reason why it’s smart to use light pots.) When you water, you want to water just enough to where you see a bit of water coming out of the bottom, not gushing or pouring out. Just enough to see a little bit, then you know the plant has enough water. To prevent over watering you can either: add more perlite to your soil, add hydrogen peroxide to your water for extra oxygen, all the while killing bacteria if any in the soil. After watering, wait a few days to water. Mj plants like a good watering and then a couple days to dry out in between watering. So it’s very easy to over water. Besides the weight of the pot, another way to test if your plant needs water is to stick your index finger a couple inches into the soil. If the soil at the tip of your finger feels almost dry, then it's time to water again. The top of the soil should be allowed to dry out between waterings if it's still moist the plant does NOT need watered. You can also use a moisture meter which will tell you the level of moisture down in the soil. You can buy them at most garden supplies or hydro shops.
Here is a picture of what over watering looks like.