Black leaves on plants are a big sign that something has gone wrong. While sometimes you can save these poor plants, often times things have gone too far at this stage to fix. Regardless of whether or not it is too late, figuring out what you did wrong can be a vital way to avoid these problems with your other plants.
Overwatering plants can also cause black leaves. Don't let your plants sit in water in a cachepot and make sure that your container has a hole in the bottom so excess water can drain out. Overwatering is the very common and a top reason for indoor plants dying. Too much water prevents the roots of the plant from taking in air and causes root rot. Be sure to use a container with bottom drip holes to prevent both overwatering and root rot.
If you see white spots building up on the surface of your soil, that is generally a salt build-up. Salts can come from your water, the potting mixtures, and fertilizers. 'Flush Watering' a plant regularly will leech out soils and will prevent this.
Temperature and Humidity
Most house plants are native to tropical areas. They prefer warm, humid conditions. To keep your plants comfortable try keeping them in areas that are between 60 and 75 degrees Fahrenheit. Anything below 55 degrees will not be plant friendly. Also make sure that your green space is properly ventilated and relatively humid.
Unfortunately, sometimes black leaves occur due to things completely out of your control. There are bacterial infections that can cause rot that turns leaves black and quickly kills out a plant. This scary situation needs to be addressed quickly or the rot can infect other plants in your garden. One of the best ways to avoid this is to get your cuttings and plants from a reliable source. Cheap, big-box stores often source their plants from unclean growing conditions. Always do research to make sure the place you buy your plants from are sourcing from a real, high-quality nursery!
Black leaves on your plants can be reversed, but in some cases are a sign of disease, fungus, or bacterial problems. Because of this risk, the safest thing to do is to remove the plant from your other plants as soon as you notice. This action can prevent a tragedy in your collection. Also be wary of Whiteflies, an insect that can spread bacterial infections between your plants!