Phlox subulata, or moss phlox (also sometimes called creeping phlox) is a slow-growing evergreen or semi-evergreen groundcover that's hardy to zone 3. It grows in a short mat and can reach 6 inches tall by 2 feet wide. Phlox subulata blooms in late April to early May with five-petaled flowers in vibrant red, pink, white, lavender or blue. The foliage is fine-textured and needle-like. Phlox is an ideal plant for a rock garden, and works well when planted at the front of garden beds, or cascading down a slope or over a wall.
Find a location in full or mostly full sun. Phlox will not flower well in the shade.
Prepare the soil by turning it with a shovel and mixing in organic matter such as compost or shredded leaves. Add organic matter to help the plants create strong root systems. Remove all weeds using a trowel or shovel prior to planting.
Plant in soil with good drainage. Phlox subulata prefers a moist soil, but will adapt to a drier situation. If the soil is heavy with clay, lighten it by working in some sand or vermiculite. Keep in mind the plant's mature width when you space the plants. Plant in staggered rows for the quickest coverage of an area.
Cut back the stems by a third to a half when flowering is finished each year. This will encourage new growth and discourage pests. If stems are not cut back, dead patches may appear.
Make new plants, if desired, by dividing and replanting the clumps after the plant has finished blooming. Water newly-divided plants well until they are established.
Provide some kind of winter cover, such as evergreen boughs, if plants are not covered by snow. This will help prevent damage to the evergreen foliage and protect the shallow roots.