The best time for transplanting phlox has to do with bloom time and species. "Phlox" can refer to over 60 species and a range of cultivars, so you need to know which one is in your garden before you decide when to transplant. The common name "creeping phlox" may refer to three species:
- Moss phlox (Phlox subulata). This rock-garden perennial is hardy in U.S. Department of Agriculture plant hardiness zones 2 through 9. It grows about 6 inches tall, and spreads up to 36 inches.
- True creeping phlox (Phlox stolonifera). This plant is hardy in USDA zones 5 through 9. It forms a mat of foliage 3 inches tall, which can spread indefinitely to naturalize an area. The flowers form on 8 inch stalks.
- Sand phlox (Phlox _bifid_a). This creeping phlox grows 6 inches tall and spreads up to 12 inches wide. It is a slow-growing plant that's hardy in USDA zones 4 through 8.
When to Transplant
Perennial plants should be transplanted or divided when they are not blooming. This lets the plants focus their energy on growing new roots and leaves instead of flowers. In general, spring-blooming plants should be transplanted in the fall, and fall-blooming plants should be moved in the spring.
- Sand phlox blooms mid- to late spring.
- Moss phlox blooms midspring through early summer.
- True creeping phlox blooms midsummer through early fall.
Transplant true creeping phlox in the spring and sand and moss phlox in the early fall. You can also divide or transplant phlox immediately after flowering, but the plants require more care at this time. If you transplant spring-blooming phlox after flowering, the plants need extra water to survive the warm summer months. If you transplant fall-blooming phlox after flowering, the plants need winter protection to keep the shallow roots safe from cold.
Where to Transplant
Prepare the planting location before you transplant phlox. Moss phlox and sand phlox both prefer a sunny location with well-draining soil. True creeping phlox grows best in full-sun or part-shade locations with evenly moist, well-draining soil high in organic matter.
Moss phlox and sand phlox grow in a variety of well-draining soils, including sandy and gravely locations, but do not tolerate heavy clay or wet soil. Amending compacted, poorly draining soil enough for these plants is difficult. If you decide to amend this type of soil, remove the soil to a depth of 18 inches, combine the soil with sand at a ratio of 1 part soil to 3 parts sand, and then use that mixture to fill in the hole. After that, plant phlox as you would in any well-draining location. You can also spread 1 to 2 inches of organic matter over the soil and work that in to a depth of 6 to 8 inches before planting.
True creeping phlox benefits from organic amendments before planting. Adding organic amendments like sphagnum peat or well-rotted compost increases moisture retention and soil fertility. Spread these amendments 2 to 3 inches deep over the soil surface, and work them in to a depth of 6 to 8 inches before planting.
How to Transplant
Water the phlox plant thoroughly a day or two before you plan to transplant it, or wait to transplant until a day or two after it rains. When you're ready to transplant, use clean gardening shears to trim back the foliage so that you can see the base of the plant. You can remove up to half of the foliage before transplanting.
Use a clean shovel or gardening fork to dig all around the plant at a distance of 4 to 6 inches from the base. Next, slide your digging tool under the plant and lift it as a clump. Phlox are shallow-rooted, so they should come up from the soil easily. If you want, you can divide plants at this time and plant them in several locations.
Plant the transplanted phlox as soon as possible after digging at the same depth it was previously growing. Firm soil around the plant, and then water thoroughly. Keep the soil moist, but not soggy, for the first two weeks. After that, water sand phlox and moss phlox when the top 2 to 3 inches of soil feels dry to the touch. Water true creeping phlox often enough to keep the soil evenly moist.