It is very important to unbox the Calathea immediately upon arrival. Test the soil, and if it is dry to the touch, water thoroughly and allow excess water to drain off. Never allow the plants to sit in water.
Provide a location indoors with bright, indirect or diffused light. Avoid a location with direct, hot afternoon sun especially in summer as this will cause the leaves to fade. Proper lighting will result in vibrantly colored leaves.
Calathea prefer evenly moist, not soggy, soil. Frequent light water and high humidity are ideal for the plants. An easy method for increasing the humidity for the plant is to mist it often or allow it to sit in a tray or saucer of moist pebbles.
Use an all-purpose houseplant fertilizer monthly during the growing season. Follow the label directions, but err on the side of under-fertilizing.
Depending on the growing conditions, you may need to repot your Calathea. If the plant has produced a lot of foliage and appears too big for its container or if it’s sending heavy roots out of the drainage holes, it may be good to give it more room. Choose a larger container and use standard potting soil for indoor plants.
Yellow leaves—Yellowing of leaves can indicate either over or under watering. If the plant is allowed to sit in water and its center leaves become yellow, the roots may be damaged, which is life-threatening. Lower leaves turning yellow could be a sign of under watering. Note that the lower leaves will fade and die as the plant grows; this is natural.
Brown, brittle leaf margins—Low humidity or exposure to low temperatures can result in brown, brittle leaf edges. If your water is high in minerals and salts, these can build up in the soil and cause brown, curled edges. If you see a white residue on the soil surface, it may be excess minerals. Flush the soil with distilled water or repot the plant. Irrigating with distilled, filtered or rai water is best. Keep the plant in temperatures 62-81°F and away from heaters or drafts. Avoid wetting the leaves when watering. Remove any affected leaves or leaf parts, as a brown or yellow leaf will never heal.
Insects—Spider mites and mealy bugs can prey on Calatheas. The best defense from insect pests is to maintain the plant’s health with proper watering, humidity and light. A weakened plant may succumb to opportunistic bugs. Spider mites appear as tiny white or tan bugs on the underside of the leaves and are present with fine webbing during major infestations. Mealybugs are cottony-looking and are usually found on the stems and in the joints of the leaf/stem connection. Treat infestations with insecticidal soap applications, neem oil, and beneficial nematodes. Follow the label instructions.