Tips on How to Grow Petunia from Seeds

Time Frame when plants are receptive to flower initiation: Days 14 – 21; 3 – 4 leaves.

Flowering Type: Long Day Plant – long days required for flowering.

Specific Flowering Mechanism: Flowering is affected by day length, irradiance and temperature.

Germination – Optimum conditions for seedling development that begins the day the crop is sown until cotyledon expansion.

Expect radicle emergence in 3 – 5 days.

Cover: Do not cover the seeds.

Media: • pH: 5.5 – 5.8

Light: Light is necessary for germination. Provide a light source of 10 – 100 foot candles (100 – 1000 lux) if utilizing a chamber.
Moisture: Saturated (5) for days 1 – 3. On days 4 – 6 reduce moisture to wet (4). Reduce further beginning day 7 to medium Humidity: 100% until radicle emergence then reduce to 40%.
Dehumidify: Provide horizontal airflow to aid in drying down the media through evapotranspiration, allowing better penetration of oxygen to the roots.

 Temperature: 72° – 76°F (22° – 24°C) until radicle emergence. Gradually reduce to 62° – 65°F (16° – 19°C) as cotyledons expand.

Finish Bulking/Flower Initiation – Optimum conditions during the vegetative period, beginning at transplant, needed for the root to reach the edge of the container; AND to make the plant receptive to flower initiation.

Media: pH: 5.5 – 5.8 Yellow upper leaves may indicate iron deficiencies when pH is > 6.6.

Light: Petunias need long days to flower. To initiate bud under short days, extend day length to 13 hours. Under long day, low light conditions, supplemental lighting of 350 – 500 foot candles (3500 – 5000 lux) may be necessary. Temperature: After transplant, Petunias require temperatures > 55°F (13°C) nights for the first 6 weeks to initiate flower bud development. After bud set, the night temperatures can be lowered to 50°F (10°C) to encourage basal branching and compactness. However, lower temperatures may also substantially decrease the number of flowers initiated. Downward cupping of leaves may indicate too cool temperatures in combination with overwatering. Average Daily Temperature (ADT): 67°F (19°C) Moisture: Alternate between moisture levels wet and dry Allow media to dry before re-saturating to level . Dehumidify: Provide horizontal airflow to aid in drying down the media through evapotranspiration under cool, low light conditions. Fertilizers: Under high light conditions, apply an ammonium-based feed (17-5- 17). Under low light conditions, apply a calcium-based feed (14-4-14). Under high light and long or extended days, an ammonium-based feed (20-10-20) is preferred. To prevent stretching under low light and cool temperatures, reduce ammonium and apply only calcium-based fertilizer.

Light: Full sun