Your tree may be suffering from chlorosis. Caused by an iron deficiency, chlorosis is the result of your trees inability to absorb enough iron from the soil, making it difficult for it to produce chlorophyll. Chlorophyll is the chemical that gives the leaf its green appearance.

There are several reasons chlorosis may occur. If the soil in which your tree is planted in is too alkaline (having a PH above 7.5) then it will be unable to absorb enough iron. Soil PH can be lowered by adding organic matter like compost and mulches containing pine needles. Using fertilizers containing chemicals such as aluminum sulfate, sulfur, and sulfur-coated urea can also be effective.

It is important to note here that soil low in the minerals magnesium, manganese, and boron can also result in yellowing of leaves in dogwood trees.

Additionally, damage to the tree’s roots could impact its ability to properly absorb minerals, as can over-watering and/or poor drainage which can cause roots to rot.

Red Twig dogwood shrubs do the best when they are planted in an area that receives full sunlight, but they can tolerate partial shade. These plants are not tolerant to long periods of dry soil and they require regular and thorough watering.