Hmmmm. I've used a siphon mixer for years, with my hose. When watering with the siphon attached, I don't think in terms of 'how much fertilizer' but how much WATER my garden and container plants are getting. Whether watering with or without the siphon, my goal is to water thoroughly.

With the siphon attachment taking up the correct amount of concentrated fertilizer solution all the time, my goal is to drench my plants just like I always do.

I think if you're using a hose attachment, that you should probably up the concentration because if you use the same proportion as you would a watering can, you're further diluting the mixture with the water from the hose. Alternatively, you can try to fertilize more frequently if you mix the same proportions when using the hose. I hope I am making sense.

Here's how the siphon works, in case you're interested! (Click on the link to see the photo.)

One end of the brass coupling is attached to the outdoor hose bib and the garden hose is attached to the other end. The siphon tube goes into a solution filled bucket. This particular brand of siphon, the Hozon, automatically takes up the concentrated solution at a rate of 1 part fertilizer to 16 parts water.

Here is a link that might be useful: {{gwi:35444}}

The siphon sounds like the way to go in that it just sucks the solution out of the bucket so you have more control over the concentration. The way the sprayer bottle that I bought seems to work is that as the solution is getting sucked out, more water enters the bottle reducing the concentration of the fertilizer in the bottle. This makes it extremely difficult to control the amount of fertilizer being applied.