Ortho makes one with a rate adjustment and I love it. No more fertilizing a gallon at a time. That took me hours to do. It sprays, so I use it for foliar feeding, too.

When you say "rate of application" are you talking about flow volume per minute? If so, I know what you mean. When watering with a wand you can shut the rate down to next to nothing so you're not blasting baby plants with hugh volumes of liquid. The Ortho sprayer is nice but it doesn't allow you to minimize this volume per unit of time...can be problematic for blasting soil mix out small containers and blasting baby plants, and wasteful when trying to fertilize individual small containers. I tried adding a kitchen sink sprayer to the end of an Ortho sprayer but the pressure differential just caused leakage where the hose and sprayer were connected, appears to have been designed that way to prevent buildup of excess pressure.

Tom

you boyz need a siphon mixer! (so do i!)... tom, you're good at mathy things... what concentration of miraclegro would i have in my bucket to make this thing work right?

i have a hose-end sprayer (ortho) that i love, but this would be even better...

Here is a link that might be useful: siphon mixer