We have been growing Sunflowers for quite a few years now. Saving our seeds each season to plant again in the next.
We grow two varieties. The Giant Sunflower with large (bone) white seeds and the Russian Black Dwarf with black and white Zebra stripped seeds.

Russian Black Dwarf. This variety only grows to about 2 metres (6ft 6in) at a maximum but many are a lot shorter than that.

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Russian Black Dwarf seed on our coffee table.

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Sunsetflowers. Russian Black Dwarf in the foreground and Giant in the back.

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The Giant ones are over 3 metres (9ft 10in) tall this year. The tall pole above the flowering beans is about 4 1/2 metres (14ft 9in)

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From last seasons harvest.

Tips for Growing

Give them lots of support or expect them to fall over once the blooms begin to form.
Sunflowers can be safely planted out up to 2 weeks before the last expected spring frost. Sunflowers can take a chill or two.
Sunflowers do not require fertilizing, however, the better their diet, the larger the flowers and the more seeds you will get.
To harvest wait until the large heads nod downwards then check the reverse side of the flowers. They are ready to cut from the stem when they turn from green to a yellow-brown. A close look will reveal the tiny petals covering the developing seeds have dried and now fall out easily exposing the tightly packed mature seeds. Cut the heads with at least 30cm (about 1ft) of stalk still attached. Brush off all of the dried petals then hang them face down in a warm, dry place that is well-ventilated and protected from rodents and bugs. Keep the harvested seed heads out of humidity to prevent spoilage from moulds and let them cure for several weeks. You may want to place a bucket or tray under the heads to catch any seeds that fall out by themselves. When the seeds are thoroughly dried dislodge them by rubbing two heads together, or by brushing them with your fingers or a stiff brush. Allow the seeds to dry for a few more days then store in airtight glass jars in the refrigerator to retain flavour or somewhere cool and dry for next seasons germination.
Chickens love Sunflower seeds. You don't need to dehull the seeds first but it helps if you crack the husks slightly with a rolling pin before you throw them into the coop. Make sure you give your Chickens plenty of grit to help them digest the seeds.
Sunflower seeds are rich in vitamins, proteins, and minerals, as well as linoleic acid which helps the body metabolize fats properly. They contain about 24 to 27 percent protein, only slightly less than an equal weight of ground beef. Furthermore, sunflower seeds contain about twice the iron and potassium and about 4 times the phosphorus of beef. Raw sunflower seeds also contain vitamins B and E, and a dash of vitamin A. Sprouted, they also contain vitamin C.

Thanks for reading and happy growing.
Remember! 'Ye ARR what ye eat.'