Yes, you can plant creeping phlox in October in most zones as long as your ground isn't frozen. Fall is one of the best times to get this ground cover started. Cool air and warm soil give your new plants ideal conditions for growing roots.
I've done creeping phlox fall planting for three seasons now and the results convince me every time. Plants I set out in mid-October put on more flowers the following spring than ones I plant in April. My fall-planted phlox on the front slope bloomed twice as full in its first spring as the spring-planted group on the back slope. The reason is simple. Fall plants get extra months of root growth before they need to spend energy on flowers.
Your roots keep growing in soil temps above 40 degrees even after the stems stop putting on new growth above ground. In most areas, your soil stays warm enough for roots well into November or December. The air might feel cold, but the ground holds heat much longer. This hidden growth period gives your October plants a strong root network. Spring-planted phlox won't catch up to that head start until midsummer.
Timing matters based on your zone. The Old Farmer's Almanac says to plant at least one month before your first hard frost. If you garden in zones 3 through 5, get your plants in by early October at the latest. You have more time in zones 6 and 7 where mid-October works well. Zones 8 and 9 give you the most room since you can plant into November with no frost worries.
When deciding when to plant creeping phlox, fall beats spring for one more reason. Garden centers mark down their perennials in September and October to clear stock before winter. In my experience, I've picked up healthy gallon pots for half the spring price at local nurseries. The plants look a bit tired from sitting in pots all summer. But they perk up fast once you get them into real ground with room to spread.
Follow these steps for the best October results with your new plants. Dig your hole twice the width of the root ball and just as deep. Water each plant with a full gallon right after you place it in the ground. Then spread about 2 inches of pine straw or bark mulch around each plant for winter root protection. Pull the mulch back from the stems so moisture doesn't sit against the crown.
Skip the fertilizer for your fall plantings. You don't want to push tender new leaf growth that the first frost will burn. Let your roots grow on their own through winter. Save your first feeding for early spring when you see fresh green growth coming up. Mark your planted spots with small stakes so you don't step on them during winter yard cleanup.
Read the full article: Creeping Phlox: Complete Growing Guide
