In my experience calatheas go into dormancy during the harmattan season. They just stay “ungrowing” and because the humidity levels drop significantly in harmattan the might loose most or all their leaves if not cared for.
Notes on Care
Remember that your Calathea (Marantaceae in general)
🍃Love humidity. And with reduced humidity in harmattan it is recommended that you group your Calathea with other large-leaved plants. The large-leaved plants will not only create shade and filter light, but they would also provide good humidity for your calathea. Misting your leaves daily with a spritz bottle or a humidifier may be helpful.You could also place a tray with gravel under your pot, to collect excess water and create humidity for your plant.
🍃 At about this time of the year the direction of the sun tends ro change, check to ensure that your calatheas are not being exposed to direct sunlight. They prefer medium to bright indirect light. Direct sunlight will cause leaf burn
🍃 Marantaceae does well in temperature conditions between 18°C – 30°C. So avoid keeping in cold air-conditioned spaces and windows with direct light and heat.
🚿 Because harmattan is hot with low humidity, soil tends to dry out really fast. Calatheas are not drought tolerant plants, ensure to keep their soil moist (but not damp) this season. You may need to adjust your watering schedule. They thrive in moist soil and would prefer not to be over-watered or under watered
🍃 It is recommended that they are not potted in oversized pots to avoid over watering the soil and prevent the plant from trying to over compensate with its roots.
🍃 Marantaceae can curl up their leaves in extreme hot or cold conditions to conserve energy, if this goes on for extended periods the leaves may not recover from curling up.
🍃 They love nutrient-rich well-drained potting soil. Can be fertilized once a month with liquid organic fertilizer. However, learn about each Marantaceae type you are growing to know their feed requirements