When leaves turn yellow, do they lack water or fertilizer. eg money plant, morning glory, papaya.?

There can be a whole host of problems. The first is of course nitrogen fertilizer defiecency most common. However defiecencies of iron, zinc, magnesium and sulfur can look the same. In addition, flooding conditions can cause these symptoms. Flooding (super saturated soil) inhibits the roots uptake of these nutrients. Then there are bacterial and fungal diseases that can cause it. Most likely however it is a nitrogen defiecency give 'em a shot of miracle grow or Peter's 20-20-20 and you should be alright.