Creeping phlox (Phlox subulata) is a popular choice for groundcover, known for its dense mats of foliage and vibrant spring blooms. Growing this perennial from seed offers a satisfying way to establish extensive plantings, though it requires specific steps to ensure success. This guide will walk you through the entire process, from seed preparation to the ongoing care of your established plants.
When to Plant Creeping Phlox Seeds
The optimal timing for planting creeping phlox seeds depends on your approach, whether direct sowing outdoors or starting indoors. For outdoor direct sowing, late autumn or early winter is recommended. This allows seeds to undergo natural cold stratification over winter, mimicking their natural germination cycle.
Starting seeds indoors offers more control and an earlier start. Sow seeds indoors 8 to 10 weeks before your region’s last expected spring frost. This ensures seedlings are robust enough for transplanting once outdoor conditions are mild.
Gathering Your Materials
Before beginning the planting process, gathering all necessary materials streamlines the operation. You will need:
Creeping phlox seeds, preferably from a reputable supplier, to ensure viability.
Seed-starting trays or small pots with drainage holes.
A sterile, well-draining seed-starting mix.
A fine-misting spray bottle for gentle watering.
Plant labels to keep track of your planted seeds.
Clear plastic domes or plastic wrap for maintaining humidity.
Seed Preparation: The Cold Stratification Process
Creeping phlox seeds require cold stratification to break dormancy, mimicking natural winter conditions. To begin, mix your seeds with a small amount of moist, sterile medium like vermiculite or sand. Ensure the medium is damp but not waterlogged.
Place this mixture in a sealed plastic bag or lidded container. Refrigerate at 35-40°F (1-4°C) for four to six weeks. This consistent cold and moisture exposure prepares the seeds for successful sprouting.
Step-by-Step Planting Guide
After cold stratification, fill seed-starting trays or pots with lightly moistened, sterile mix. Gently firm the soil surface to create a level bed.
Scatter seeds thinly over the prepared soil. As creeping phlox seeds need light for germination, lightly press them into the soil surface or cover with a very thin layer (no more than 1/16th inch) of fine vermiculite.
Mist gently to settle seeds and ensure good seed-to-soil contact. Place trays in a warm location (65-70°F / 18-21°C). Covering with a clear plastic dome or plastic wrap helps maintain humidity for germination.
Caring for Your Creeping Phlox Seedlings
Once seedlings emerge (typically 2-3 weeks), adjust their environment to promote healthy growth. Provide plenty of light, ideally from a grow light positioned a few inches above for 12-16 hours daily. This prevents leggy growth, ensuring strong, compact stems.
Water seedlings carefully from the bottom by placing trays in a shallow pan of water for 10-15 minutes. This allows soil to absorb moisture without disturbing delicate seedlings or promoting damping-off disease. Maintain good air circulation, perhaps with a small fan, to deter fungal issues.
Transplanting and Ongoing Care
When seedlings have developed at least two sets of true leaves, transplant them into larger pots. Gradually acclimate them to outdoor conditions (hardening off) by exposing them to increasing periods of outdoor time over 7-10 days. Choose a planting site with full sun to partial shade and well-draining soil.
Space young plants 12-18 inches apart, allowing ample room for their spreading habit. Water regularly during their first growing season to establish a strong root system. Once established, creeping phlox is drought-tolerant and requires minimal care, benefiting from occasional weeding and light pruning after flowering to maintain a dense form.