Zinnia Planting Guide
Arrival of Seeds
Zinnia seeds are supplied dry and ready for sowing. If you are not sowing immediately, store them in a cool, dry place away from direct sunlight.
- Keep seeds dry.
- Store at room temperature in an airtight container until ready to sow.
Sowing & Germination
- Sow indoors from Spring time, or later if sowing directly outdoors once all risk of frost has passed.
- Use a free-draining seed compost in 9cm pots, large-cell plug trays or coir modules, as zinnias dislike root disturbance.
- Sow seeds on the surface of the compost and lightly cover with a thin layer of vermiculite.
- Cover pots or trays with clear plastic or a propagator lid to maintain humidity until seedlings emerge.
- Germinate at 18–20°C.
- Seeds typically germinate within 5–14 days.
- Keep the compost evenly moist but never waterlogged, as seedlings are susceptible to damping off.
Planting & Growing
- Pot on as soon as the roots hold the compost together, taking care to minimise root disturbance. Do not allow plants to become pot-bound.
- Harden plants off before planting outdoors after the last frost.
- Plant in a warm, sheltered position in full sun.
- Space plants 30–45cm apart.
- Water during dry periods, allowing the soil to drain freely between waterings.
- Feed weekly with a half-strength liquid fertiliser during active growth.
- Provide support for taller varieties using individual stakes or a support frame if required.
Additional tips
- Zinnias thrive in warm, sunny conditions and perform best during hot summers or when grown in a greenhouse or polytunnel in cooler climates.
- Deadhead regularly or cut flowers frequently to encourage continuous blooming throughout summer and into autumn.
- Ensure good air circulation around plants to reduce the risk of fungal diseases.
- Avoid overwatering, particularly in cool or humid weather, as zinnias are prone to damping off, mould and stem rot.
Grower FAQs
Zinnia seeds germinate best at 18–20°C and usually emerge within 5–14 days. Cool temperatures, overly wet compost or allowing the compost to dry out can all delay or reduce germination. Keep the compost evenly moist (not waterlogged) and maintain consistent warmth.
Yes. Once all risk of frost has passed and the soil has warmed, seeds can be sown directly into a sunny, well-drained position. Thin or transplant seedlings carefully to leave 30–45cm between plants, taking care to minimise root disturbance.
Zinnias require full sun and regular deadheading to flower continuously. Too much nitrogen-rich fertiliser can encourage leafy growth at the expense of blooms, so feed weekly with a balanced liquid fertiliser at half strength during active growth.
Remove faded flowers regularly or harvest blooms frequently for cut flowers. Keep plants watered during prolonged dry spells, feed regularly, and grow them in a warm, sunny position with good air circulation. With proper care, zinnias will continue flowering from summer until the first autumn frosts.
If you need further horticultural support, please contact us at info@romanbanknurseries.co.uk
