I've been spraying
compost tea for a year now with a Solo backpack sprayer. I can't remember where I got these settings from, but I use a spray head at 30 psi (on the pressure dial, #2) to get maximum pressure without injury to tea organisms.
Straining the tea before spraying has proved one of the more pesky tasks. No matter the gauge of the screen, I still get particles small
enough to clog the head in there. At least I can have the sprayer explode on me from the tank or the wand without worrying about chemical blindness! (Though my microbiome is probably 84% compost organisms now.)
I understand some folks use a "trombone sprayer", an old fashioned thing you put in a
bucket and pump. I have one of those too, but that's too cumbersome for acreage, especially on hillsides! Those can handle slug tea without clogging, and will probably be best for comfrey+nettle tea application.
There's a lot of magic in compost tea. I mean, magical thinking. The science is young and its proponents are cagey about specifics, but I'm putting most of my eggs in that basket. I've already seen encouraging results...just don't ask me about specifics ;)
Books & papers I've read about compost tea make it sound as though some awful beasties will colonize your every batch of tea if you don't clean your sprayer well enough. This might happen anyway if your compost is foul! What terrifying responsibility coupled with vagueness.
How do you clean your sprayer? I hose mine down with well
water through a firehose nozzle...most importantly, immediately after using the gear. It
should probably then dry in the sun, but not for long enough to irradiate the plastic. The parts should probably be spread out for maximum air circulation and solarization, but I don't do that because I'd probably lose them, and pathogenic microorganisms could more easily get into the workings of the sprayer if it were disemboweled across a table. Vinegar solution seems possible and easy but maybe that's overkill.
I bet ozonated water is a really sound choice, unfortunately it's expensive to make and not available for purchase. What about hydrogen peroxide solution? Since that eventually breaks down to water, only cost makes that unattractive, unless there is some easy reaction by which it can be produced at home.
EDIT: The august Eric Fisher reminded us on this forum that most of the aerobic organisms in tea are helpful, so creating that environment is the main aim. His book was the main reason I jumped into teas last year, having thought about it for years after Dr Ingham. Teas or "soil soup" are also mentioned glowingly in the excellent books "Dirt: The Erosion of Civilizations" and "The Hidden Half of Nature: The Microbial
Roots of Life and Health". Nobody extolling these teas has gotten all neurotic about cleaning application equipment to laboratory sterility --- at least, no one's said so!
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