GARDEN CULTURE Where to Plant The most important consideration for healthy phlox is to plant it in the proper site. Most species of phlox, such as P. paniculata, P. carolina, and P. maculata, prefer consistently moist, fertile soil. This closely mimics the conditions found along river courses and floodplain edges where these species naturally occur. In a garden setting, when the soil dries out these species are more likely to develop disease. This is especially true for powdery mildew on P. paniculata. Other species like P. amplifolia and P. pulchra can tolerate slightly drier conditions, and while they still prefer moist soil, they don’t require as much consistency as P. paniculata. Phlox pilosa prefers relatively dry, well-drained soil and can rot if grown in soil that stays wet for long periods of time. In terms of sun exposure, all of the above mentioned species do best in full sun to light shade. Powdery Mildew Powdery mildew is a disease common to many garden plants and is the main concern gardeners have when growing garden phlox. It is ubiquitous in the environment and only requires proper weather conditions to develop on the leaves and stems of susceptible hosts. Powdery mildew usually first appears when days are warm and nights are cool. Cool nights provide the high humidity that enables spore germination (initiation of new infections) and warm days provide the low humidity for spore dispersal (spreading of existing infections). The disease itself is typically only cosmetic. Lower leaves are the first ones affected and frequently fall off by midsummer. If an infection becomes more severe, the defoliation will extend further up the plant. In extreme cases, plants can lose so many leaves that they are unable to survive the winter. Instances like this were observed in Mt. Cuba Center’s trial; however, this level of severity is unlikely to occur in most home gardens where there are not hundreds of phlox growing in close proximity. Site selection, as mentioned above, is critical in preventing disease development. However the easiest way to avoid powdery mildew on Phlox paniculata is to select disease resistant cultivars like 'Jeana', 'Delta Snow', and 'David'. The powdery mildew resistance ratings listed on the chart on pages 14-15 are based solely on observations from our trial. Because of the added disease pressure caused by growing so many phlox in one location, the disease ratings may be more severe than what most gardeners will likely experience. Spider Mites Spider mites are small arachnids that feed on plant juices inside the leaves. Phlox paniculata can be prone to spider mite outbreaks, especially when the weather is hot and dry. Natural populations of beneficial mites typically help to control spider mites. However, periods of hot, dry weather can cause spider mite populations to increase much faster than the beneficial mites. Active infestations cause yellowing of the foliage and often produce webbing on the undersides of the leaves. Most home gardeners will not see significant outbreaks like what was observed in Mt. Cuba Center’s trial simply because we had uncommonly high numbers of phlox in one garden. If damage does become significant, spider mites can be controlled without chemicals by spraying a hard, steady stream of water upwards at the undersides of the leaves. This knocks down enough mites to keep damage at tolerable levels. Design When deciding where to plant phlox in your garden it’s important to think about how tall the plants will be when they bloom and more importantly, how tall the neighboring plants will be. This is especially valuable since neighboring plants can be used to obscure the loss of any lower leaves due to powdery mildew or drought stress. There are cultivars available in almost any height, so phlox can easily be incorporated into any garden. Fragrance is also an important consideration when designing with phlox. Strongly fragrant selections, like those listed on pages 14-15, have a scent that is noticeable several feet away. This can add greatly to enjoying time spent on a patio or sitting area. Maintenance Phlox are relatively easy to maintain throughout the year, especially when planted in a cool and moist, yet sunny location. In periods of drought, additional water may be necessary to keep plants healthy and disease free. Aside from that, phlox can be cut back to the ground in the fall or late winter each year. In the proper location, they are reliably hardy throughout the mid-Atlantic region. Powdery mildew 12 Spider mite damage is visible on the top of the leaf as an interveinal yellowing, while webbing can often be observed on the underside.