Sunflower Tall (Helianthus annuus giganteus) Sow Indoors: February- June. Sow Outdoors: March- June. Spacing: 8-12" / 18-28cm. Flowering Height: 72" + / 166cm +. Flowers: July- September. Sunflower Tall (Helianthus annuus giganteus):These giant sunflowers are easy to grow, producing huge yellow flowers on strong stems. Produces seeds that are loved by many species of birds, so excellent for drawing in wildlife. Flowers can grow up to around 30cm across, displaying petal-like florets in stunning yellow. Hardy annual. Giant yellow flowers on tall strong stems, a must for your garden. Hardy Annual.Indoor Planting: Sow seeds 1cm deep in trays of moist compost, be careful not to over-water. Store in a warm place at an approx. temperature of 13-16-°c (56-60-°f).Growing On: When the seedlings are strong enough to handle they can be transplanted into bigger pots or trays. Do not overcrowd the plants and keep in a warm, light position. Once all chance of frost has passed the plants can be transplanted direct into your desired location in May. Harden off first.Outdoor Planting: Sow seeds 0.5cm deep in flowering location, thin to above spacings. The Sunflowers may require staking.