How to Grow Sunflower Seeds

Grow Guide #2325
Family: Asteraceae
Binomial name: Helianthus annus
Life Cycle: Annual

This 'How to Grow' guide details everything a home gardener needs to know to plant, grow and care for Sunflowers (Helianthus annus).

When to Sow Sunflower Seeds

Sunflower is a warm season flower. Use the table below to identify the best time of year to sow sunflower seeds in your climate.

  JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Cool
Temperate
Sub-Tropical
Tropical
Arid

Preparation

Sunflower plants are best grown in full sun. Choose a location that will receive at least 6 hours of full sun each day.

Sunflower plants need a well drained soil enriched with plenty of organic matter. Prepare soil by weeding it thoroughly, digging it over to loosen it and adding aged animal manure or compost. Keep the area free of weeds until planting. Learn more about preparing soil for planting here.

Sunflower plants can be grown in containers. If possible choose a variety that’s recommended for container growing. Use a good quality potting mix and make sure your container is large enough for mature plants; a minimum of 40 litres is recommended for sunflowers. During the growing season, keep in mind that container grown plants may need additional fertiliser to encourage healthy growth.

How to Sow Sunflower Seeds

Sunflower seeds do not require any treatment (eg soaking, stratification) before sowing.

Sunflower seeds can be sown directly into the garden OR seedlings can be raised in trays or other containers and transplanted to the garden once established.

Sow Direct

  1. Sow seeds directly in the garden 10mm deep and 30-50cm apart.
  2. Keep soil moist but never wet or dry.
  3. Seeds should germinate in around 7-14 days at a soil temperature of 21-30°C.
  4. Young seedlings will need protection from pests, pets and weather until they are established.

Raise Seedlings

  1. Fill trays, punnets or jiffy pots with a good quality seed-raising mix, or use soil starter pellets.
  2. Sow seeds 10mm deep.
  3. Keep soil moist but never wet or dry.
  4. Seeds should germinate in around 7-14 days at a soil temperature of 21-30°C.
  5. Transplant seedlings to the garden once they have their first true leaves and are large enough to handle (usually 5-10cm tall).
  6. Plant out, spacing plants 30-50cm apart.

How to Grow Sunflower

Sunflower plants may need watering during the growing season. Water when the soil is dry about 5cm below the surface (test this by scratching away a little soil with your finger). Water deeply in the early morning or late afternoon. Avoid watering the leaves of plants to avoid fungal diseases. Learn more about watering here.

If soil was well prepared no extra fertiliser should be necessary. In poor soil or to give your plants an extra boost, application of a high-potassium fertiliser or one formulated for flowering plants can be beneficial:

  • Apply slow release fertiliser at the recommended rate when transplanting or when seedlings are 5-10cm tall.
  • Apply liquid fertiliser at the recommended rate and frequency while plants are fruiting or flowering.

Sunflower plants may need to be supported as they grow. Depending on the expected size and height of the plant, use a stake, bamboo cane, trellis or string lines to support plants. Make sure you have the support in place when you sow seed or transplant seedlings to avoid disturbing the plant's roots later.

Sunflower plants should flower in approximately 80-90 days.

If growing sunflowers for cut flowers, use sharp snips or secateurs to cut the longest stems possible, removing the lower leaves and placing the stems immediately in a clean bucket of water. Learn more about cutting and conditioning homegrown flowers here.

To harvest sunflower seeds cover whole flower heads with netting or a paper bag once the petals have died to protect the seeds from birds and other predators. Alternatively, cut the entire flower head, leaving some stalk attached, and hang it upside down in a cool, dry, airy place. The seeds are ready to harvest when they become loose and easy to dislodge from the flower head. Hold the head over a bucket and bang it hard against the side to dislodge the seeds. Scrape any remaining seeds out of the flower head using a fork. Seeds can be eaten raw or roasted and stored in an airtight container.

Common Problems when Growing Sunflowers

Like all plants, sunflower is susceptible to some pests, diseases and other problems. Below is a list of the most common problems gardeners encounter when growing sunflower plants:

  • Worms eating flowers
    Armyworms, cutworms and other caterpillars can all eat the buds or flowers. Young caterpillars burrow into the buds, eating the petals so flowers do not open properly, or consuming the seeds once the flower has matured. Monitor plants and remove any caterpillars you see. If necessary use insect exclusion netting to physically protect the plant, or spray with Dipel.
  • Wilt
    Fusarium wilt and verticillium wilt are diseases caused by soil-borne fungi. The fungi enter a plants’ roots and prevent water and nutrients from moving through plants. Leaves and branches will wilt, dry off and die and leaves may yellow. There is no cure for wilt but choosing resistant varieties, disposing of affected plants and soil, practicing good garden hygiene and crop rotation will all help to prevent it spreading.
  • Animal eating fruit
    Possums, birds and other animals can ruin a large percentage of your harvest overnight. Physically exclude pests by using netting or cages, or try spraying plants with a pungent homemade spray made from garlic, fish oil or mustard.
  • Rust fungus
    Rust (Puccinia sp.) is a fungal disease that causes brown to orange raised spots or patches to appear on foliage. Fungal spores are spread by wind or water to neighbouring plants, especially in temperatures of 10-20C and when humidity is high. To manage rust, space plants to avoid overcrowding, grow them in the recommended amount of light (eg full sun), do not over fertilise crops, remove dead plants and practice crop rotation. Read more about rust fungus here.
  • Powdery Mildew
    Powdery mildew is caused by fungal spores reproducing on the leaves of plants. First showing as white spots on leaves, affected areas can spread quickly to cover the entire leaf surface. While rarely fatal, powdery mildew can reduce yields. Water plants at soil level (not on leaves) to prevent spreading spores, allow good air flow between plants, remove affected leaves and if necessary spray with an appropriate fungicide or homemade spray. Read more here about powdery mildew here.
  • Slugs and Snails
    Slugs and snails are molluscs that feed on tender leaves and shoots, mostly at night, leaving slimy trails behind them. Control them by removing their hiding places, keeping free range poultry, collecting them by torchlight or by placing traps. Read more about slugs and snails here.

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