What is the NVS site?
Believe it or not, the 20 ft. maize plant I didn't feed anything. It was too much of a pain to get into the back of the garden with the hose to feed it. Every year I do throw down cotton seed meal and kelp meal at the beginning of the spring though. I didn't use manure for the past two years. I just use grass clippings, shredded newspapers, pine needles, straw, and leaves that I throw in the garden during the late fall every year. I don't want my garden too rich, or I would be breeding for plants that may only do well in the most rich soils.
I'm in central New Jersey. I believe my zone is considered 6b. Jersey is a great place to live if you like gardening. Jersey's name is actually "the garden state." This year was a bit unusual, because we had some very hot weather this year, with many days going over a 100 degrees.
The important thing is to find the best material out there that has the best chance genetically of getting that large.
Yes, it is a yardstick. Everyone in the USA still uses inches, feet, miles, etc. If we could get the rest of the world to do the same, we would.
The very tall green thing next to me is a long gourd. They can get much longer. This year is my first attempt at growing a long gourd. That long gourd was approximately 6 foot 3 inches tall, which is how tall I am. I built a 17 foot tall trellis this year and grew the gourds up the trellis.
The one pic is of an english vegetable marrow. It was over 30 pounds, but it should have been much bigger. The person from the UK that gave me the seeds had it at 109 pounds. I find that they don't do as well in my area as in the UK. I think it much more humid where I am, and the summer temps probably get warmer. They have a tendancy to rot on the vine where I am.
There are many types of corn that get large. Most are from Mexico and Central America. Mexican June White gets fairly large. Generally, I find they get about 15-16 ft. The type I grow is called Jala Valley Landrace Maize, and that is probably one of the tallest in the world. I believe the current world record from Iowa in 1946 at 31 feet tall was from Jala. I don't always get ears on my plants; especially the really tall ones. Many of the plants are around 17-18 ft. tall, but I had one this year at 19 ft. and another at 20 ft. I have another giant maize (still don't know the name of it) plant that is still in the growth phase, and may surpass all of them, depending on when we get frost. The ears on Jala get about 2 ft., but the actual cobbs get about 18 inches long.
In my opinion, the three best sunflower varieties in the world for height are:
'Bott's Strain' which were originally bred by Richard Bott in Michigan.
'Craven' sunflowers, which were bred by Norm Craven in Ontario, Canada.
Richard Hope's Giant Single sunflowers, which were bred by Richard Hope in the UK.
All three sunflowers can get around 20 feet tall. Although, I never seem to get them that tall. I have a lot of problems in my area with these stem borers that do some serious damage to my sunflowers. I have no pests with my corn; so you can see the difference.
Hope I didn't miss any questions!