How to Fertilize double-leaved sundew?
No fertilizer needed; carnivorous plant absorbs insect nutrients

double-leaved sundew · Drosera binata
Also known as: old man's eyebrow
Under glass, grow in mix of equal parts fertiliser-free peat substitute and sand, in full light with shade from hot sun. The compost should be kept continually moist in the growing season by standing the container in a tray of soft (lime-free) water, such as rainwater. During the winter, plants enter a period of dormancy so keep plants moist, not sodden. Outdoors grow in wet, peaty, acidic, nutritionally poor soil in full sun. See Carnivorous plant cultivation
No fertilizer needed; carnivorous plant absorbs insect nutrients