Moss Phlox
Phlox subulataUSDA | Grow Zone
3-9Outdoors all year in zones 3 to 9. Anywhere colder, keep it as a houseplant.
- Light
- Full sun, 6 hours
- Water
- Every 1-2 weeks
- Humidity
- 40-60%
- Temperature
- 60-75°F
- Difficulty
- Beginner
- Growth
- Moderate
- Mature size
- 6-12 in tall
Moss Phlox (Phlox subulata) is a charming perennial known for its vibrant spring blooms and ground-covering habit. Native to North America, it thrives in sunny gardens and rockeries, making it a popular choice for gardeners seeking low-maintenance beauty.
Ask Vesper about Moss Phlox
Ideal temperature
60-75°F is where it grows fastest.
Spacing and harvest
- Mature size
- 6-12 in tall
- Plant apart
- 12-24 in
- Frost
- Hardy: survives frost
Everything it needs
9 essentials at a glance
Watering
Moss Phlox prefers well-drained soil and should be watered deeply but infrequently.
During the growing season, water every 1-2 weeks, allowing the soil to dry out between waterings. In hot summer months, increase frequency to weekly if the soil dries out quickly. Signs of over-watering include yellowing leaves and root rot, while under-watering may cause wilting and browning leaf edges.
Light
Moss Phlox thrives in full sun, requiring at least 6 hours of direct sunlight per day for optimal growth and flowering.
It can tolerate partial shade but may produce fewer blooms. Ideal placement includes sunny borders or rock gardens, where it can receive ample light without being shaded by taller plants.
Soil
The ideal soil for Moss Phlox is sandy to loamy, with a pH range of 6.0 to 7.0.
It requires excellent drainage to prevent root rot, so incorporating sand or gravel into the soil mix is beneficial. A recommended potting mix includes a blend of potting soil, sand, and perlite for aeration.
Humidity
Moss Phlox prefers moderate humidity levels, typically around 40-60%.
To increase humidity, mist the plants or place a humidity tray nearby. Conversely, if humidity is too high, it may lead to fungal issues, so ensure good air circulation around the plant.
Temperature
Moss Phlox thrives in temperatures ranging from 60-75°F (15-24°C) and is hardy in USDA zones 3-9.
It can tolerate cold temperatures down to -30°F (-34°C) but may struggle in extreme heat above 90°F (32°C). During summer, provide some afternoon shade in hotter regions to prevent stress.
Fertilizing
Use a balanced fertilizer with an NPK ratio of 10-10-10, applying it every 4-6 weeks during the growing season.
Reduce or eliminate fertilization in fall and winter. Signs of nutrient deficiency include stunted growth and yellowing leaves, indicating a need for additional nutrients.
Pruning
Prune Moss Phlox in early spring before new growth begins.
Use clean, sharp pruning shears to remove dead or damaged stems and to shape the plant. Deadheading spent flowers throughout the blooming season encourages more blooms and prevents self-seeding.
Repotting
Repot Moss Phlox every 2-3 years or when it becomes root-bound.
Choose a pot that is 1-2 inches larger in diameter. Signs it needs repotting include roots growing out of the drainage holes and stunted growth. To repot, gently remove the plant from its current pot, loosen the roots, and place it in fresh potting mix.
Propagation
Moss Phlox can be propagated through stem cuttings or division.
For stem cuttings, take 4-6 inch cuttings in spring or early summer, remove lower leaves, and place them in a moist potting mix. Keep the cuttings in a warm, humid environment until roots develop. Division can be done in early spring or fall by carefully separating clumps and replanting them.
When it's unhappy
Yellow leaves
Why it happens
This can be caused by over-watering or nutrient deficiency.
How to fix it
Adjust watering practices and consider fertilizing with a balanced fertilizer.
Root rot
Why it happens
Root rot occurs due to overly wet soil and poor drainage.
How to fix it
Ensure proper drainage and reduce watering frequency. Remove affected roots and repot in fresh, dry soil.
Powdery mildew
Why it happens
High humidity and poor air circulation can lead to powdery mildew.
How to fix it
Improve air circulation around the plant and avoid overhead watering. Use a fungicide if necessary.
Wilting
Why it happens
Wilting may indicate either under-watering or root damage.
How to fix it
Check soil moisture and adjust watering accordingly. Inspect roots for damage and repot if necessary.
Care through the year
Spring
In spring, prune back any dead stems and fertilize with a balanced fertilizer to promote new growth and blooms.
Summer
During summer, ensure consistent watering, especially in hot weather, and deadhead spent flowers to encourage more blooms.
Fall
In fall, reduce watering as the plant enters dormancy, and consider applying a light layer of mulch to protect roots from cold.
Winter
In winter, protect Moss Phlox from extreme cold by covering with mulch or leaves, especially in colder zones.
Toxicity & Safety
Moss Phlox is non-toxic to pets and children. No parts of the plant are known to cause harm if ingested, making it a safe choice for gardens frequented by pets and kids.
Good to know
How often should I water my Moss Phlox?
Water your Moss Phlox every 1-2 weeks, allowing the soil to dry out between waterings. In hot weather, you may need to water weekly.
Why are my Moss Phlox leaves turning yellow?
Yellow leaves can indicate over-watering or a nutrient deficiency. Check your watering schedule and consider fertilizing if needed.
Can I grow Moss Phlox in partial shade?
While Moss Phlox prefers full sun, it can tolerate partial shade. However, expect fewer blooms in shadier conditions.
When is the best time to prune Moss Phlox?
Prune Moss Phlox in early spring before new growth begins to remove dead stems and shape the plant for better blooming.
How do I propagate Moss Phlox?
You can propagate Moss Phlox through stem cuttings or division. Stem cuttings should be taken in spring or early summer.
What soil type is best for Moss Phlox?
Moss Phlox thrives in sandy to loamy soil with good drainage and a pH of 6.0 to 7.0. Amend soil with sand or gravel if necessary.
What are common pests that affect Moss Phlox?
Common pests include aphids and spider mites. Regularly inspect your plants and treat infestations promptly with insecticidal soap.
Track this plant in your garden.
Set care reminders, log growth, and join a community of plant lovers.