Sonia,

There have
been numerous fertilization recommendations posted on various threads here on
the canna forum. You might try using the search box to get the results, but to
recap some of the basics, consider the following relative to your specific
location;

• Get
  a soil test to determine your present soil composition and needs: pH, available
  phosphate, potash or micronutrients needed. Slop soil chemistry may work but
  the soil test will determine basic requirements. Most of us tend to forgo this
  step and plants respond accordingly.
• Cannas
  respond to high organic composted additives.
• Nitrogen
  applications applied a few times (2 or 3) during the growing season is
  typically beneficial.
• Adequate
  to abundant water supply.
• Good
  pest control if applicable.
• Full
  sun if possible.

“Healthy Pretoria” will typically multiply very well given
average growing conditions. The average mature foliage height may be about 4 feet
or slightly more. The blooms may reach about a foot to a foot and a half above
the foliage. Virus issues often will affect results but I cannot see any obvious
problem from your photos. It’s difficult to judge how yours have matured.

Just for the record, the tall dark green foliage canna with
reddish blooms is not President. You may very well have received it labeled as
President but that tall growing plant is very likely canna compacta (specie
canna) that is sometimes sold as C. Robert Kemp. It is also likely the very
best specie canna for use in our garden setting needing a very tall cultivar. I
think you will find it produces viable seed and President has a much larger
bloom but does not produce seed.

Cannas, just like all plants, do deplete available soil
nutrients that need to be replaced each year to maintain health and vigor. Keep
in mind that your soil pH (soil test) will determine the availability of
nutrients present.

The above thoughts are only suggestions that might help achieve
better results and should not be construed as absolutes.

Kent

That was all so helpful Kent. It has been forever since I was last on Gardenweb forum and to my surprise I ended up on this houzz site. I immediately scrolled down to the Canna topic but once in I scrolled through the Canna queries but must not have scrolled down enough because I couldn't find a query relating to fertilization. I will have to play around with this site a bit more to familiarize myself with it as there are other plants I enjoy in my garden that I may ask help on. Thank you again. I was beginning to think no one was here to help.

What zone are you?

See

http://forums.gardenweb.com/discussions/3363550/this-years-canna-pics .

I used this:

http://www.growersupply.com/peex15calmag.html