I'm going on my third year growing Hemker mutli-headed, and yes, they are for real. I recommend growing them in pots because the seeds are very small, and the germination time seems to be a bit sporadic. I have a feeling that there is wild sunflower genes mixed in this sunflower. Soak the seeds for an hour in a cup of water before putting them in pots. Generally, the sunflowers get about 8 to 12 feet tall, and around 7 feet wide. I've been growing them in a 3 ft x 6 ft space, but I plan on growing them in a large spacing this year. If you have the room, I would grow them in about 6 ft. x 6 ft block per plant. Mine usually put out about 200-350 flowers per plant. A larger spacing will probably get you more flowers. They usually put out flowers about 50 at a time, and then new flowers come from the leaf nodes of the previous flowers, and so on.

They seem to self sow very well too. I've actually had some self sow in a part of the garden that I didn't use the following year. One seems to have crossed with an unknown single headed variety and produced a heavily branched plant with larger flowers.

Here are some pictures:
(sunflower on left is self-sown Hemker multi-headed)
(sunflower on right is self-sown unknown single-head x Hemker multi-headed)
- notice flower in front, lower left is actually part of the plant on the right.
http://www.geocities.com/sunflower_info/hem_cross1_03.JPG

Stem base of unknown single-head x Hemker multi-headed:
http://www.geocities.com/sunflower_info/hem_base1_03.JPG

Here are pictures of some of Melvin Hemker's giants:
http://www.geocities.com/sunflower_info/World_Records.html

Here are some pictures of Hemker sunflowers:
http://www.geocities.com/sunflower_info/hemker.html

Wow. Thanks Brian. I'll be sure to make some room, of which I have plenty, for these next year. The thought of spending $5 on 5 seeds made me want to check the plant out first! Thanks again for the pictures.

Make sure you don't plant the seeds very deep either. You want just enough dirt to cover the seed. The seedlings will be much smaller than other sunflower seedlings. I'm always amazed how small the seedlings are, but how large they become when full grown.
The first time I saw the prices from P&P World Record seeds, I was hesitant about paying $8 for 3 Craven seeds, but they were worth every penny and then some.
http://www.geocities.com/sunflower_info/craven15_1.jpg
http://www.geocities.com/sunflower_info/craven25_5.JPG

Where do we get hemke seeds?
When to plant?

P&P world record seeds. search under google and you'll find it! Good luck!

Is it too late to start them?

You are in Canada; so probably not too late.

Excellent- I was soaking last year's giant seeds, but then I forgot, so now all I have is a slimy mess. How log would it take before the seeds arrive?

Brian-
Incredible Pictures!