How to Grow Zinnia From Seed in Australia

Zinnias are beautiful flowers in various colours, shapes, and sizes. They are easy to grow from seed and make a great addition to any garden. 

If you live in Australia and are interested in growing zinnias, I’ve compiled some tips to help you get started and ensure you get the best results.

 

What is zinnia? 

Zinnia is a genus of flowering plants that belong to the Asteraceae family. Native to North, Central, and South America, these annual and perennial plants are known for their vibrant, colourful blooms that come in a wide range of shapes and sizes. In fact, there are over 20 species of zinnias, with the most common (and my personal favourite) species being Zinnia elegans.

The zinnia plant is herbaceous, meaning it doesn’t have a woody stem. 

What does zinnia look like?

Zinnias are flowering plants that are known for their bright, colourful blooms. The appearance of a zinnia can vary depending on the species and cultivar, but here are some common features that can help you identify a zinnia plant: 

• The leaves of a zinnia plant are opposite, meaning they grow in pairs on either side of the stem. 
• They are ovate or lanceolate in shape and can be anywhere from one to six inches long. 
• The leaves are typically a medium to dark green colour and have a slightly rough texture.
• Zinnia flowers are typically 5 to 7 centimetres in diameter
• They come in various colours, including red, orange, yellow, pink, and white, and some cultivars have bicolour or multicolour petals.
• The flower head is made up of many small disk flowers that form a flat or slightly domed shape.
• It can grow anywhere from 15 centimetres to over a metre tall, depending on the species and cultivar. 

Zinnias are beautiful and vibrant plants that add colour to any garden or flower arrangement. With their wide range of colours and sizes, a zinnia cultivar can suit almost any gardening or decorating need.

 

Zinnia uses 

Zinnias are a popular choice for gardeners like myself because they are easy to grow from seed and require very little maintenance. They prefer full sun and well-draining soil but tolerate various soil conditions. I find the best growing spots are in garden beds, containers, or as cut flowers.

In addition to being a popular garden plant, zinnias also have medicinal properties. Some species of zinnia have been used in traditional medicine to treat fevers, colds, and digestive issues. Zinnia flowers also contain compounds that have antioxidant and anti-inflammatory properties.

In addition, some zinnia cultivars are edible and can be used to add colour and flavour to salads, drinks, and other culinary creations. Zinnias can also attract beneficial insects like butterflies and bees to the garden, which can help with pollination and overall ecosystem health.

 

Best conditions for growing zinnia 

Climate 

Zinnias are warm-weather plants that thrive in hot and sunny climates. They are native to Mexico and South America and prefer temperatures between 75 and 85 degrees Fahrenheit. Therefore, the best environment for zinnia cultivation is in regions with a warm climate and plenty of sunshine.

In regions where the summers are long and hot, zinnias can be planted in the early spring and can continue to bloom until the first frost. It is best to wait until the danger of frost has passed in cooler climates before planting zinnias.

Soil

Zinnias are annual flowering plants known for their bright and colourful blooms. To grow healthy and vigorous zinnias, it is important to choose the right soil.

The best soil for zinnias is well-draining, nutrient-rich, and has a slightly acidic pH level between 5.5 and 7.5. It should be loose and crumbly, allowing air and water to move freely through the soil. A mixture of garden soil, compost, and perlite or sand can create the ideal soil structure for zinnias.

When preparing the soil for planting zinnias, it is important to remove any rocks or debris that could impede root growth. 

Adding organic matter such as compost, manure, or leaf mould can improve the soil structure and provide the necessary nutrients for the plant to thrive. It is important to avoid overwatering zinnias, as they can be susceptible to root rot and other fungal diseases. Watering should be done at the base of the plant to avoid getting the leaves wet.

 

When to plant zinnia seeds in Australia 

The best time to plant zinnia seeds in Australia is during the spring and early summer, after the danger of frost has passed, and the soil has warmed up.

As zinnias are warm-weather plants that require soil temperatures of at least 15 degrees Celsius for optimal germination. In Australia, this typically occurs during the spring and early summer months, depending on the specific region. 

Planting zinnia seeds after the danger of frost has passed ensures that cold temperatures do not damage the young plants. Additionally, planting in the spring allows the zinnias to take advantage of the long days and warm weather of the summer growing season, which is essential for their growth and development. 

By planting zinnia seeds at the right time, you can ensure that your plants have the best possible chance of thriving and producing beautiful blooms throughout the summer.

 

How to plant zinnia seeds 

To plant zinnia seeds, I’ve outlined some simple steps to help get the best results:

1. Choose a sunny location: Zinnias require at least 6 hours of direct sunlight daily. Select a well-draining area with good air circulation and nutrient-rich soil.
2. Prepare the soil: Remove any weeds and debris from the planting area. Mix in compost or other organic matter to improve soil structure and fertility.
3. Sow the seeds: Sow the seeds directly into the soil, about 1/4 inch deep and 6 to 12 inches apart, depending on the variety. Water the soil lightly after sowing the seeds.
4. Water regularly: Keep the soil moist but not waterlogged. Water the zinnias deeply once or twice a week, depending on rainfall.
5. Thin the seedlings: Once they have grown a few inches tall, thin them out so they are spaced at least 6 to 12 inches apart, depending on the variety.
6. Fertilise: Apply a balanced fertiliser every four to six weeks to promote healthy growth and blooming.
7. Deadhead: Remove spent blooms regularly to encourage more flowers to bloom.

With proper care, your zinnia seeds should germinate in 7-14 days and bloom in 8-10 weeks. I also recommend supporting tall varieties of zinnias with a wooden stick and ensuring you watch out for pests!

When to prune zinnia 

Zinnias do not require frequent pruning, but you can pinch back the growing tips of the main stem and lateral branches to encourage bushier growth and more abundant flowering. I recommend doing this when the plants are about 15 to 20 centimetres tall.

Deadheading, or removing spent blooms, is another form of pruning that can help keep your zinnias blooming all season long. You can do this by simply snipping off the faded blooms, either individually or by cutting back the entire stem that has finished blooming.

However, it’s important to note that pruning or deadheading should not be done too late in the season as it can reduce the plant’s ability to produce seeds for the following season. Generally, I recommend avoiding pruning zinnias after mid-summer to ensure the plant has time to set seeds for the next growing season.

 

FAQs

What is the best fertiliser for zinnia? 

Zinnias benefit from regular fertilisation to promote healthy growth and abundant blooms. A balanced fertiliser with equal nitrogen, phosphorus, and potassium is ideal for zinnias. A 10-10-10 or 20-20-20 fertiliser is a good choice for zinnias.

How do I know my soil is well draining?

One way to determine if your soil is well-draining is to perform a simple percolation test. Dig a hole about 30 cm deep and wide, fill it with water, and allow it to drain completely. Then refill the hole with water and measure the time it takes to drain completely. If it takes less than 2-3 hours for the hole to drain, your soil is considered well-draining.