A hardy houseplant, the dragon tree (Dracaena marginata) thrives outdoors in U.S. Department of Agriculture hardiness zones 10 and 11, according to the University of Florida IFAS Extension. With a potential growth height of 10 feet or more, this dracaena variety can provide long-term decoration in your garden with the right care. When the tips of the plant's leaves turn black, it's a sign the plant needs a slight change in care to stay healthy.
As a tropical plant, the dragon tree likes warm, humid weather with indirect light. Spritzing the leaves periodically helps with the humidity, but you're not always in control of the weather if you keep your plant outdoors. When the temperature falls lower than the plant likes, the tips of the leaves tend to turn black. Placing the plant where it receives too much direct sunlight can burn the leaf tips and edges, also causing them to blacken. Black tips won't hurt the plant long term, but continued extreme temperature fluctuations can kill the dragon tree.
Dracaena marginata plants prefer well-draining, moist soil. They are relatively drought-tolerant, but when they don't receive enough water, the tips of the leaves can turn brown or black as the plant conserves energy. Check the soil to make sure it's moist about 1 inch below the surface; if it's not, increase your watering schedule, especially during the hottest months of the summer. Conversely, if the plant receives too much water, the leaf tips can blacken. Dragon trees don't like soggy soil; change the soil to a better-draining variety, such as one containing perlite, if necessary, or add gravel inside the base of the pot to increase drainage.
Using a water-soluble, balanced fertilizer every two weeks during the growing season is usually sufficient for dragon trees. Over time, however, minerals from the fertilizer -- and sometimes from tap water -- can cause mineral buildup or deficiencies in the soil that cause the leaf tips to blacken. Dragon trees don't tolerate salt or fluoride well, but changing the soil every couple of years can help houseplants. For outdoor plants, leach the excess minerals out of the soil by pouring filtered water over the roots for several days. Dracaena marginata needs boron and calcium to thrive, so make sure those are components of the fertilizer you apply.
Dragon trees are susceptible to fungal infections, such as Fusarium leaf spot, that cause the leaf tips to blacken and curl. This occurs when the leaves stay too wet, allowing the fungus to grow and reproduce in the damp areas, often along the tips and edges of the leaves. The spots start out as a rust or tan surrounded by yellow, then turn black as that section of leaf is killed. Left unchecked, the fungus can kill the plant. Watering the plant from the base and reducing spritzing can help prevent the spread of the disease, and a fungicidal soil drench can help the plant fight off the fungus if it's spread to the main stem.
- University of Florida IFAS Extension: Dracaena Marginata Red-Edged Dracaena, Madagascar Dragon-Tree
- Learn 2 Grow: Dracaena Marginata
- University of Florida IFAS Extension: Fusarium Leaf Spot of Dracaenas-Resistance of Species and Cultivars
- University of Vermont: Dracaena Marginata
- LiDonni Nursery and Landscape: Dracaena / Marginata