Crotons are tropicals that are sensitive to cold. Yours may be reacting to the cool, damp weather we've had. It's a good idea to gradually move your plant indoors for the winter. But we are supposed to get near the freezing mark soon, so be prepared to move yours indoors at any moment. Fertilize with a balanced formula, keep it in bright light and keep the soil moist but not soggy.
Hibiscus leaves yellow with age and drop, making way for others to grow.
Some yellowing of leaves is nothing to worry about. But this plant, too, could be reacting to the change in weather. Warmth and a good amount of sunshine will keep it green during the winter months. Hibiscus like more potassium, represented by the last number. However, I'd decrease fertilization and let the plant rest this winter.