The dragon tree (Dracaena marginata) begins life as a tuft of long and skinny leaves, but branches and develops trunks as it ages, growing to 20 feet tall. Those leaves are narrowly rimmed with red in the species type, but add an extra yellow stripe for the “Tricolor” cultivar or a more flaming band of red for “Colorama." All these dragons will get snuffed if left out-of-doors in U.S. Department of Agriculture plant hardiness zones lower than 10 to 12, and are usually grown as houseplants. Brown or browning leaves can be caused by a variety of issues.
The Aging Dragon
Each leaf on a dragon tree lives about two years. Therefore the lowest ones, which are also the oldest, will dry up and drop off when their time comes. There’s not much you can do about that sort of browning, and it doesn’t hurt the plant’s naturally lean and leggy look. If you prefer short and squat, you can cut the branches back, and they should produce new leaves below the cut.
The Doused or Dehydrated Dragon
Brown tips on leaves are often caused by either over- or under-watering. Since this dragon prefers to be kept on the thirsty side, the problem is usually too much moisture rather than too little. To avoid putting out its flame, water the plant only when the soil is dry at least 2 inches below the surface. Keeping the plant in a light soil that contains lots of sand or shredded bark will also help. If there are brown speckles as well as tips on the leaves, your dragon is most likely dehydrated instead, which you can prevent by watering it whenever that top 2 inches is dry.
The Poisoned or Overfed Dragon
Fluoride may be good for your dentin, but it is not good for your dragon tree, and will also tinge its tips with brown. If your water is fluoridated, you can gather rainwater for your plants instead, or use a reverse osmosis filter to clean your water. A buildup of salts in the soil, usually due to over-feeding, can also cause such browning. To prevent it, fertilize your plant with an all-purpose houseplant food only once a month from spring to fall, using just 1/2 teaspoon of crystals per gallon of water. Don’t feed it at all during the winter.
The Chilly Dragon
Speaking of winter, don’t position your dragon tree where it will be hit by blasts of cold air when doors open and close. On freezing nights, make sure the leaves don’t touch any window glass. Those that soften and curl when they turn brown have usually been hit by sudden cold. Keeping the dragon tree a little back from the panes is usually a safe bet, as it prefers bright indirect light to full sunlight anyway.