How to Grow Sunflowers from Seed

Growing sunflowers from seed is one of the most satisfying things you can do in a summer garden. The seeds are large and easy to handle, germination is fast and reliable when conditions are right, and within a few months you go from seed to a plant that can stand three metres tall. Get the basics right and sunflowers are one of the least troublesome plants you can grow.

Choosing Your Seeds

The first decision is what type of sunflower to grow. Standard tall varieties like 'Russian Mammoth' and 'Giant Single' reach two to three metres and produce one enormous head. Multi-headed branching varieties like 'Velvet Queen' and 'Claret' produce many smaller flowers over a longer period — ideal for cut flowers. Dwarf varieties like 'Teddy Bear' and 'Big Smile' stay under 50 centimetres and suit pots and small gardens. All types are grown from seed in exactly the same way.

Direct Sowing Outdoors

The simplest method is direct sowing into prepared ground after the last frost date — late April in the south of England, May in colder regions. Choose the sunniest spot available and prepare the soil by forking it over to a depth of 30 centimetres and incorporating a generous amount of garden compost. Sow seeds 2.5 centimetres deep and 10 centimetres apart. Once seedlings have two pairs of true leaves, thin them to the final spacing — 45 centimetres for standard varieties, 90 centimetres for giants. Direct-sown sunflowers establish quickly and develop stronger root systems than transplants, making them more drought-tolerant later in the season.

Starting Indoors

If you want an earlier start, sow individually in 9-centimetre pots of multi-purpose compost from mid-April. Cover the seed with 2.5 centimetres of compost, water gently and place in a warm spot — a heated propagator or a warm windowsill will achieve the 18°C to 24°C soil temperature that sunflower seeds prefer for germination. Germination typically takes five to ten days. Grow the seedlings on in the brightest spot available — a south-facing windowsill or under a grow light — to prevent legginess. Harden off over seven to ten days before planting outside after the last frost date.

Transplanting and Aftercare

Sunflowers dislike root disturbance, so handle transplants gently and keep the root ball intact. Plant at the same depth as in the pot. Water in well and protect from slugs in the first few weeks. Once established — about four weeks after transplanting — sunflowers need little intervention other than watering during dry spells. They rarely need feeding in reasonably fertile garden soil, though a balanced feed in midsummer gives heavy feeders like giant varieties a useful boost.

Germination Troubleshooting

If seeds fail to germinate, check soil temperature first — below 15°C, germination stalls. Old seed loses viability rapidly; always buy fresh seed for best results. Sowing too deep (more than 2.5 centimetres) slows emergence. Seeds sown in waterlogged soil will rot rather than germinate. If only half your seeds germinate, sow a few extra to ensure you get the number of plants you want.