Question
i transplanted two yew tress about eight months ago. one tree is thriving and the other is yellowing and loosing needles. the one in question was planted in yhe same potting soil as the other but i do remember a white mold in near the bottom of the bag when i was finishing. ive checked for scale ect and would like to save it if its not two late.

Answer
Hi Brian,

It is difficult to know if the white mold that you saw is responsible for the problem.  Most likely, it was just a secondary mold growing on the woody potting mix.  However, it may suggest that the plants were being kept too wet.  

The main problems that I find on yew are Phytophthora root rot and environmental problems.  If the problem is Phytophthora root rot, the roots would look discolored and they may be sparse.  You can only know this by digging up the plant and examining the roots.  If the roots do not look healthy, then you may want to remove the plant now.  Phytophthora root rot generally kills yew plants (or makes them look so bad that you remove it).  Healthy roots will have grown out of the root ball and should appear white or light colored.  They will be tough and not fall apart if you tug on them.  

The Phytophthora fungus produces spores which can survive in the soil for a long time.  The longer the plant remains in the soil, the more spores that will form.  Phytophthora root rot is more severe in soil that is heavy (high clay content) and/or poorly drained.  It is also more associated with wet spots such as low areas or where down spouts drain.

If the roots appear normal, it is likely that the problem is due to one or more environmental factors.  Ensure that you have good drainage around the plant because these plants do not like "wet feet".  They prefer well drained soil.  If you do not know your soil pH, you may want to have it tested.  You can purchase a pH test kit at your local garden center or you can send it to a lab for testing, but this may take longer. Yews do not like pH that is extremely high or low; 6.0-7.0 is optimum.  Other problems that can cause yellowing include low fertility (you can fertilize with a tree and shrub fertilizer), improper watering, and too little light.  You will have to rule out all of these as potential causes.  

Even though your two plants may be planted in the same general area, there are often difference in soil type, especially near houses.  When homes are built, they often bring in top soil and sand which are often left on-site after building.  The trees may actually be planted in entirely different soils.

Good luck with your plants.
--Jen