Q.winter hanging basket
I do water when the pot feels light. But have never fed.
First, check the plant for spider mites or other pests to make sure they aren't responsible for plant problems. If you are up for it, this may be a great opportunity to start over with ivy cuttings. Ivy roots easily. (Older vines are thicker and tend to have fewer leaves.) Potting mix breaks down over time and plants need repotting every 2-3 years or when you notice they aren't thriving anymore. If you slide the plant out, you may see a mass of roots and very little potting soil. Nothing will do well in that environment, fertilized or not. If you cut a straggly ivy vine back to soil level, new vines will emerge. Try top dressing or mixing in some compost into the potting mix. Ivy is not a heavy feeder. I fear normal plant fertilizer will encourage leggy or excessive growth. If you feel it is necessary, use it half strength and choose one with more nitrogen than potassium and potash. I'm attaching a link to an article that discusses how to care for ivy and take cuttings. Notice that the writer mentions cultivars with more petite leaves. These may do better over time in containers. https://aggie-horticulture.tamu.edu/newsletters/hortupdate/hortupdate_archives/2001/jan01/art11jan.html