Sowing: Sow indoors from February, 8 to 10 weeks before last frost.
Petunias flower early and are covered with stunning blooms. They like the sun and often bloom within two months from seed and continue throughout the season until killed by the frost. They are easily cultivated, requiring rich soil and full sun. They grow best in high-moisture areas with well-drained soils, but can adapt to most soil types. Established plants are drought resistant, requiring less dry-weather maintenance than other plants.
Plant seeds 6mm (¼in) inch apart, in rows 7cm (3in) apart and gently firm (especially the corners), so you don't get erosion when watering. Do not cover the seed, as the seeds need light to germinate.
Provide light and constant warmth of 21 to 27°C (70 to 80°F). Use a bottom heat source for best results. F1 hybrids tend to germinate better at the higher end, at around 27C (80F). The soil temp should not fluctuate and must not drop below 21°C (70°F). Finely mist and cover seed tray with plastic or paper to conserve moisture.
Check the compost for dryness regularly. If this is the case, add a little warm clean water from below, being careful not to over water. Too much water can kill seedlings, as it can spread "damping off fungi", and encourage other moulds and diseases.
Germinates usually takes 10 to 21 days depending on soil and temperature conditions. Remove cover as soon as seeds sprout. Keep moist and do not use cold water as it lowers the soil temp and weakens tender seedlings.
When seedlings are large enough to handle, transplant and grow on in cooler conditions, around 13 to 16°C (55 to 60°F) for stocky plants.
Gradually acclimatize to outdoor conditions for 10 to 15 days before planting out after all risk of frost, 30cm (12in) apart in a sunny spot on light well drained soil. For pot plants, transplant the seedlings into 7.5cm (3in) pots, grow cool, well ventilated and give plenty of light, but shade from direct sun.
Cultivation:
When plants are 5 to 10cm (2 to 4in) tall, and ground is warm, transplant to their final positions in pots or into the garden, spacing 20 to 30cm (8 to12in) apart. Plant in a full sun location. They will tolerate light shade but blooming will be reduced. Use a low-nitrogen/high-phosphorus fertilizer sparingly. Do not overwater or over fertilise, Overwatering will yellow and kill the plants.
After planting into baskets, when established give them a good spray from a watering can. The weight of the water flow will produce a perfect cascading habit.
For denser plants and more flowers, pinch or shear when 15cm (6in) tall and keep faded flowers picked.
Petunias are sticky and will attract greenfly so keep an eye on them. Don't over water in the winter and keep them well ventilated.
Overwintering:
Petunias are generally sold and grown as half hardy annuals (they will tolerate slight frost and flower in the first year from seed) but in their native countries of Brazil and Argentina they are a perennial.
The plants can be over wintered by lifting in the autumn, trimmed back to about 15cm (6in), then potted up into a well drained potting compost. The plants can then be placed on a cool 13°C (55°F) well lit window sill and planted out in the early summer.
Fresh seeds are packed in ziplock bags!
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