I have tall phlox that started out looking healthy; as they progressed the leaves have turned yellow with green and did not bloom. The ones at the front of the house did just fine, they have kept their green color and bloomed beautifully. Do you have a suggestion as to my problem?
The Gardener’s Answer
Hello, Gloria: Tall garden Phlox (Phlox paniculata hybrids) is a wonderful addition to any sun-loving, perennial garden. When they are planted in ideal conditions, they are prolific summer bloomers. As with any new addition to the garden, it may take a year for the plant to become established. If you just planted them this spring and the ones growing up front are not given the best growing conditions, it may be that they are using their energy to establish roots instead of the flowers. Are your phlox receiving the same amount of sunlight? The more sun the better when it comes to this perennial. What about the drainage? Does the area in the back of the house drain as well as the front? If not, the plant may be suffering from root rot and if you have had as much rain as we have had this summer, in combination with poor drainage this could certainly be the problem. Yellowing foliage can also be an indication of nutrient deficiency; both iron and nitrogen deficiencies can result in chlorotic foliage. This is most common in soils with a high pH. You can have your soil tested to make sure this is not the problem. The most common problem we see with phlox is powdery mildew, but from what you have described it does not sound like this is the problem with your phlox. The foliage would have more of a white cast to it than a yellow one if this were the case. You can take a sample of your phlox to a local garden center with a knowledgeable staff and they will be able to look at your sample and give you a more definitive answer.