On the hydrangea flowers with missing petals (actually they are called bracts)- hydrangea virescence Is likely. Plants with confirmed virescence should be destroyed.
If the blooms had petals/bracts and they disappeared, then Japanese beetles or rose chafers are the culprits. To confirm virescence send samples to MSU Diagnostic lab---
English ivy leaves small and yellow- causes include too much water, too little nitrogen.
Boxwood- there are many things that can cause this problem. Details of watering method and how much water is applied, type of soil, when and how much fertilizer applied, any stem cankers or peeling bark present, any discolored stems, any evidence of scale or other insects, especially on backs of leaves-- these are other signs to looks for.
Here are some links with common symptoms and causes -
If you have more questions, or can provide more details, please write again. Thanks for using Ask an Expert.