Phlox germinate and grow quickly, so in most cases you're best off direct-sowing your seeds.
But, if springtime is late in your area, start them indoors 4-6 weeks before the potential last frost.
Scatter seeds evenly over the soil and cover them with 1/8" fine soil. Darkness is required for germination. Then carefully transplant outdoors when the first true leaves appear. Seeds should germinate in 5-10 days.
- Seed Treatment: None required.
- When to Plant Outdoors: As soon as the soil is consistently 65°F to 70°F.
- When to Plant Indoors: 6 to 8 weeks prior to last spring frost.
- Seed Depth: ⅛"; some sunlight required to germinate.
- Seed Spacing: Plant or thin 1' apart in dryer conditions; 2' in humid regions or when planting in consistently-irrigated beds.
- Days to Germination: 5 to 10 days at 70°F; 7 to 14 days at 65°F.
- Transplanting Tips: Harden off for a few days prior to transplanting. If using biodegradable pots, score and moisten before placing the entire container into the bed or pot.
Add a general-purpose fertilizer when planting them, then once a month after that.
Drummond's Phlox is a cool season plant, so it may slow down in the heat of high summer. If this happens, cut the plants back dramatically to just 5cm (2"), and await a second burst of blooms as autumn approaches. Be sure to keep irrigated in hot weather, especially in containers.
Mulching will help retain moisture and moderate soil temperatures, but be sure to keep mulch away from the plant stems. At the end of the season, cut back annual phlox to soil level. Cut perennial phlox 2" above the soil level, and clean up any debris; it will regrow again in the spring.
Hardy annual Phlox varieties often survive the first few light touches of frost. However, they will not survive a hard frost or freeze. Perennial Phlox varieties go dormant after a killing frost, until next spring. At this time, it is recommended to cut the plants down to the ground.