What Causes Brown Leaves on Anthurium?

With one creamy-white, finger-shaped flower rising from each of their glossy red, pink or white spathes, anthuriums (Anthurium andreanum) are dramatic outdoor ornamentals in U.S. Department of Agriculture plant hardiness zones 11 through 12 or striking indoor plants elsewhere. Their few problems include browning leaves. Anthuriums' sap is mildly toxic, so keep them away from chewing pets and handle them with care.

Pruning injuries and insect damage expose anthurium leaves to bacterial blight infection. Xanthomonas bacteria enter the wounds and the pores along the leaf's margins. Through a natural process called guttation, droplets of excess fluids drain through these pores at night. The bacteria feed on the fluids, multiply and spread. The diseased leaves turn yellow, with water-soaked margin spots that expand into brown, dead V-shaped patches. The plants slowly wilt and die.

To discourage Xanthamonas, keep you anthuriums dry and dispose of infected plants as soon as you see symptoms. Ready-to-use Bacillus subtilis QST 713 bacterial spray controls the disease. Use it outdoors after slipping your houseplants’ containers into disposable covers. Dress in a long-sleeved shirt, long pants, socks and shoes, put on a respiratory mask and waterproof gloves and coat the entire plants until they drip with the solution. Wait four hours before watering them. During cool, wet weather, treat them weekly, or as often as the product label recommends. Separate your work gloves and clothes from your other laundry and wash them in hot water and detergent.

Excessive fertilizer turns a potted anthurium's lower leaves yellow, with gradually enlarging brown tips. Fertilize your plants monthly in spring and summer with liquid, high-phosphorous fertilizer. For indoor plants, dilute 1/4 teaspoon, or the label's recommended amount, of 10-15-10 fertilizer in 1 quart of water. Give outdoor plants 1 teaspoon per 1 gallon of water. During fall and winter, switch to a 10-10-10 formula mixed at the same strength and apply it every month to six weeks.

Treat an over-fertilized anthurium by removing the whitish salt crust on the surface of the potting mix. You can also remove between 1/2 to 2 inches of the potting mix. Clear the pot's drainage holes, put the plant in a sink or shower and fill the pot to the brim with lukewarm tap water. Let it drain completely and repeat -- for heavy salt buildup, you may need to do eight rinses. After scrubbing the salt from the saucer and outside of the pot, let them dry. Cover the root ball with fresh potting soil, water just enough to moisten it, and let it dry to the touch before watering again. After a month, fertilize at one-half strength before returning to your normal fertilizing schedule. Precautionary leaching every four to six months eliminates future buildup.

Very dry air may brown anthurium's tips. Misting the plants weekly with a spray bottle or setting them atop pebble-filled saucers of water provides enough humidity to keep them green. Displaying them in indirect light near bright windows prevents browning from too much sun.