How to Fertilize Klapper's hedgehog cactus?
Very dilute low nitrogen cactus feed in warm growth season

Klapper's hedgehog cactus · Echinocereus klapperi
Grow under glass in a loam-based potting compost with added extra grit. Water moderately when in growth, not at all when dormant. Apply a balanced liquid fertiliser 2 or 3 times in the growing season see houseplant cacti and succulent cultivation
Very dilute low nitrogen cactus feed in warm growth season