Giant Sunflower

[McMouse]

Best I've ever managed was 9 feet tall. Any suggestions for extra growth?

[anneasquith]

rose feed

[rowanwitch]

dig out a biggish hole (about the size of a bucket and fill with a mixture of good quality potting compost, water retaining granules and blood fish and bonmeal (about a handhull of WR granules and a plactc cup of BFB... the trick then is to start the plant indoors as early as possible in a good light and keep the soil moist while it is outside.... stake well to avoid windrock which damages the roots... and top up the feeding with with something like tomato feed or liquid seaweed once a week after it has been in the ground about a month

And make sure you grow a variety that has been bred for taller plants