How to Fertilize slender pencil orchid?
Half-strength orchid feed every two to three weeks in active growth

slender pencil orchid · Dendrobium mortii
Plants are best grown mounted on cork bark or wood if sufficient humidity can be provided. Alternatively, grow in a basket in an epiphytic, medium grade, bark-based potting mix with added perlite, moss, or coir. As with many orchids, they grow best when the roots are slightly restricted. Therefore, avoid over-potting or frequent root disturbance. Provide bright light and sufficient humidity by misting regularly throughout the growing season. Reduce watering and feeding in winter until warmer temperatures initiate flowering and new growth in spring. See indoor orchid cultivation
Half-strength orchid feed every two to three weeks in active growth