The biggest problem with phlox depends on which species you grow. Tall garden phlox battles powdery mildew all summer long. Creeping phlox faces a different set of threats like root rot and spider mites. Knowing your species helps you fight the right enemy.
I grow both types in my garden and the contrast is dramatic. My tall phlox gets a white powdery coating on its leaves every July without fail, no matter how much I space the plants for air flow. Meanwhile, my creeping phlox growing just ten feet away has never shown a single spot of mildew in over five years. In my experience, P. subulata resists mildew because its tiny needle leaves and low growth let air flow through the mat. If mildew is your main concern, creeping phlox gives you the phlox look without that headache.
The phlox diseases that do threaten creeping types are less visible but more dangerous. Phytophthora root and crown rot is the number one killer according to NC State Extension. This water mold attacks roots in soil that stays wet too long after rain or irrigation. You won't see it coming until whole sections of your mat turn yellow, wilt, and die. Southern blight is another fungal threat in warm humid climates, causing white mold at the base of stems during hot summer months.
Phytophthora Root Rot
- Cause: Water mold that thrives in poorly drained, soggy soil and attacks the root system from below ground level.
- Symptoms: Sections of the mat turn yellow, wilt during warm days, then collapse and die back within a week or two.
- Prevention: Amend heavy clay soil with coarse sand before planting and choose sloped sites where water runs off fast.
Spider Mites
- Cause: Hot dry conditions in summer create ideal breeding grounds for these tiny pests that suck sap from foliage.
- Symptoms: Leaves develop a dusty gray or stippled look, and fine webbing appears between stems in bad cases.
- Prevention: Blast plants with a strong water spray twice a week during dry spells to knock mites off and raise humidity.
Rabbit Damage
- Cause: Penn State Extension notes rabbits cause more damage to phlox than deer, which tend to leave this plant alone.
- Symptoms: Stems chewed down to the base in spring when new growth is tender and rabbits are raising young nearby.
- Prevention: Install low wire fencing about 18 inches tall around new plantings until plants are well established.
The full range of phlox pests and problems also includes nematodes in sandy southern soils. These microscopic worms damage roots and stunt growth without any visible signs above ground. If your plants look weak despite good sun, water, and drainage, nematodes could be the hidden cause. A soil test from your local extension office can confirm their presence.
Prevention works better than treatment for almost every phlox issue. Make sure your soil drains well and plant in full sun with good air flow. Water at the base instead of overhead. Check your foliage once a month for early signs of mites or disease. Catch problems early and most of them stay minor annoyances rather than garden disasters.
Read the full article: Creeping Phlox: Complete Growing Guide
