I have 3 clematis in different areas of yard that display chlorosis of only a part of the plant?
- As noted in the above link, there are a number of nutrient deficiencies that can cause leaves to yellow and which leaves are being affected is a clue to the cause. Because the yellowing is occurring in all 3 plants at other locations in the yard, it is not localized to one area. Frequently when plants not thriving and their leaves are yellowing, we assume the soil is missing nutrients and add fertilizers. However, sometimes the problem is too much of a “good thing”. For example, excess phosphorus can prevent uptake of micronutrients like zinc or iron. The best way to determine whether a nutrient is lacking in the soil is to send samples for analysis. If the required nutrients are present in the right amounts, then the problem is more physical like soil compaction for example. Here is a link to a very good explanation of chlorosis and what can cause it
If you want to get the soil tested there are a number of laboratories in Ontario that do soil tests including the University of Guelph. Here is a link to their laboratory.