Planting Guide: How to Grow Zinnias from Seed
This guide will help you understand how to successfully grow Zinnias from seed to full flower, offer tips to ensure healthy growth, and explore different varieties of Zinnia to plant in your garden.
Flower Variety Identification
Common Name: Zinnia
Scientific Name: Zinnia elegans
Family: Asteraceae
When to plant Zinnias in your climate
Not sure what your climate is? See our climate charts.
Cool: September, October, November, December
Temperate: August, September, October, November, December
Sub-Tropical: August, September, October, November, December
Tropical: April, May, June, July, August, September
Arid: January, February, March, April, May, June, July, August, September, October, November, December
Step by Step guide to growing Zinnias
1. Choosing the Right Time to Plant
Zinnias are annuals and are best planted after the last frost when the soil has warmed up. They grow quickly, so you can enjoy their blooms within a couple of months of planting. You can start zinnias indoors to get a jump on the growing season or sow them directly in the garden once the weather warms.
When to plant:
- Indoor sowing: Start seeds indoors 4-6 weeks before the last frost.
- Direct sowing: Sow seeds directly into the garden after the last frost when the soil temperature is around 21°C.
2. Selecting the Ideal Location
Zinnias thrive in full sun. Choose a location that receives at least 6-8 hours of sunlight per day. Zinnias prefer well-drained soil, and while they can tolerate poorer soils, they will perform best in rich garden soil.
Location needs:
- Full sun (6-8 hours of sunlight)
- Well-drained, fertile soil
- A spot with good air circulation to prevent disease
3. Preparing the Soil
Zinnias thrive in well-drained soil that’s rich in organic matter. If your soil is heavy or clay-based, it’s a good idea to add compost to improve drainage and quality.
Steps for soil preparation:
- Loosen the soil to a depth of 15-30 cm using a garden fork or anything you can find that will work.
- Remove any rocks, weeds, or debris from the area.
- Mix in organic compost to improve the soil and improve drainage.
4. Sowing Zinnia Seeds
Zinnias are easy to start from seed, and they germinate quickly. You can either start them indoors or sow them directly into the garden once the soil has warmed up.
Indoor sowing method:
- Fill seed trays or pots with a well-draining seed-starting mix.
- Sow seeds about 0.5 cm deep and cover lightly with soil.
- Water gently and keep the soil moist but not waterlogged.
- Place the trays in a warm, sunny spot or under grow lights.
- Zinnias germinate quickly within 5-10 days.
Direct sowing method:
- Sow seeds 0.5 cm deep and about 15-30 cm apart, depending on the variety.
- Cover lightly with soil and water gently.
- Keep the soil consistently moist until seedlings emerge.
- Thin seedlings to about 15-40 cm apart once they are 10-20 cm tall to allow room for growth.
5. Watering and Care During Germination
Zinnias require regular watering during the germination and seedling stages. After they are established, they are relatively drought-tolerant and need less frequent watering.
Watering tips:
- Water lightly and consistently during germination, keeping the soil moist but not soggy.
- Once established, water deeply but infrequently, allowing the soil to dry out between waterings.
- Avoid overhead watering, as zinnias can be prone to fungal diseases.
6. Fertilising Zinnias
Zinnias don’t require heavy fertilisation, but a little boost of nutrients can help them produce more blooms.
Fertiliser tips:
- Use a balanced fertiliser or organic compost.
- Apply a light dose of fertiliser when planting and again once the plants start to flower.
- Be careful not to over-fertilize, as too much nitrogen can lead to lush foliage but fewer flowers.
Three Growing Tips
1. Deadhead Regularly to Promote More Blooms:
Removing old flowers will encourage zinnias to keep producing new blooms throughout the growing season. This will also help the plants look tidier and prevent them from going to seed too early.
2. Space Plants Properly to Prevent Disease:
Zinnias can be prone to fungal diseases, especially in humid conditions. To prevent this, make sure to space your plants properly (15-40 cm apart) to allow for good air circulation. This will help reduce the risk of powdery mildew and other fungal infections.
3. Water at the Base to Avoid Fungal Diseases:
Zinnias are susceptible to powdery mildew and other fungal diseases, especially if their foliage stays wet for too long. To avoid this, water your plants at the base and avoid getting the leaves wet.
Common Diseases and Pests
While zinnias are generally hardy and easy to care for, they can be susceptible to a few common pests and diseases. Knowing how to prevent and treat these problems will help keep your plants healthy and blooming.
Powdery Mildew:
Powdery mildew is a common fungal disease that appears as a white, powdery coating on the leaves. It’s more common in humid conditions or when plants are overcrowded. To prevent powdery mildew, space plants properly and water at the base to keep the foliage dry. If powdery mildew appears, remove affected leaves and treat with a fungicide if necessary.
Leaf Spot:
This fungal disease causes small brown or black spots on the leaves. To prevent leaf spot, avoid overhead watering and provide good air circulation around your plants. If leaf spot occurs, remove infected leaves and apply a fungicide.
Aphids:
Aphids are small, sap-sucking insects that can damage zinnias by stunting their growth and causing deformed leaves. To control aphids, spray the plants with a strong stream of water to knock the insects off, or use insecticidal soap.
Spider Mites:
These tiny pests can cause yellowing and stippling of the leaves. Spider mites thrive in hot, dry conditions, so keeping the plants well-watered can help prevent infestations. Use insecticidal soap or neem oil to treat spider mites if necessary.
Slugs and Snails:
Slugs and snails can chew holes in the leaves of young zinnia plants. Use organic slug baits or create physical barriers, such as copper tape, around the plants to deter these pests.
Aftercare For Zinnias
Once your zinnias are established, they require relatively little maintenance. However, a few simple steps will help keep your plants healthy and blooming all summer long.
Watering:
Water zinnias deeply once or twice a week, depending on the weather. Allow the soil to dry out slightly between waterings, as zinnias prefer well-drained conditions. Be sure to water at the base to keep the foliage dry and prevent fungal diseases.
Deadheading:
Regularly deadhead flowers to encourage more flowers. This will also help keep the plants looking tidy and prevent them from going to seed prematurely.
Fertilising:
Apply a balanced fertiliser every 4-6 weeks during the growing season to encourage continuous growth and blooming. Be careful not to over-fertilize, as this can lead to excessive foliage at the expense of flowers.
Pest and Disease Control:
Regularly inspect your zinnias for signs of pests or diseases, and take action early to prevent problems from spreading. Keep the garden area clean and free of debris to reduce the risk of pests.
