Philodendron 'Black Cardinal' - BioLook at the colour! You don't often see a plant with this beautifully dark colour. The Philodendron 'Black Cardinal' is an indoor plant that really stands out. As well as being a show stealer with its dark leaves, the Philodendron also has an air purifying effect. The Philodendron prefers full or partial shade, needs water twice a week and plant food twice a month. Good to know: too much water and sunlight will discolour the leaves of this plant.