Mandevilla Plants- Is there a specific fertilizer or home made remedy?

Mig27521650
by Mig27521650

I have two Mandevilla plants by my front door. They actually survived the winter (SC) in my garage. Although they have blooms all flowers look faded by the sunlight. These are a full sun plant I believe and my neighbors are looking very vibrant. Is there a specific fertilizer or home made remedy?