Fertilizing rainwater

[malteseproverb]

Interesting! Thank you all for the info. I'm not sure if I want to risk playing around with the rainwater as I still might end up frying my plants with acid. I might just use tap water when I fertilize and flush with rainwater right after. As it is, I like to run a lot of water through the plants and get them thoroughly wet, so I usually apply fertilizer first and flush after with plain water. I could still use the cal-mag or epsom salts though. I would consider MSU but it seems like a pain to store and use. And there's a frightening thread on GardenWeb about it that I can't get out of my head.

[Roberta]

Originally Posted by malteseproverb

Interesting! Thank you all for the info. I'm not sure if I want to risk playing around with the rainwater as I still might end up frying my plants with acid. I might just use tap water when I fertilize and flush with rainwater right after. As it is, I like to run a lot of water through the plants and get them thoroughly wet, so I usually apply fertilizer first and flush after with plain water. I could still use the cal-mag or epsom salts though. I would consider MSU but it seems like a pain to store and use. And there's a frightening thread on GardenWeb about it that I can't get out of my head.

You might want to invest in an inexpensive pH meter (online or your local hydroponics store) I just got an RO system, was concerned that I might have an issue with my existing fertilizer (since I won't have an easy chance to get the MSU pure-water stuff for a few weeks) I mixed up my regular brew (the RO water is about 20 PPM TDS as opposed to the 300 I start with... another meter worth having). I used plain old Miracid fertilizer, and behold, the pH was a very nice 6.8. (To get that pH with tap water I have to add about a tablespoon per gallon of vinegar, anything in the fertilizer to acidify the water is no match for all that calcium carbonate) So... depending on your water, it might actually be fine. (If you live in an area that gets acid rain, your results may be different...) You really can't know what you are working with unless you test. If you don't want to buy a meter, pH test paper is even cheaper (though not as accurate) Knowledge is power...

[Orchid Whisperer]

Originally Posted by malteseproverb

Interesting! Thank you all for the info. I'm not sure if I want to risk playing around with the rainwater as I still might end up frying my plants with acid. I might just use tap water when I fertilize and flush with rainwater right after. As it is, I like to run a lot of water through the plants and get them thoroughly wet, so I usually apply fertilizer first and flush after with plain water. I could still use the cal-mag or epsom salts though. I would consider MSU but it seems like a pain to store and use. And there's a frightening thread on GardenWeb about it that I can't get out of my head.

I am not sure about Philly's water quality, but can't imagine it is sufficiently bad that you would need to flush it out of the medium right away. Actually, you can probably buffer your rainwater a lot if you just mix a certain amount of tap water with the rain water. Tap water is almost always buffered and pH adjusted to 7 or 8 before it gets into the water mains (the Flint, MI water quality problems were largely due to improper pH management before the water entered the pipes, resulting in lead dissolving from pipes into the tap water).

You can look up the water quality for just about all USA water treatment utilities online (water quality is part of my professional work). The water department should be able to tell you important things about your water, such as electrical conductivity (EC), total dissolved solids (TDS), pH, hardness, and alkalinity. The units of measurement are just as important to write down as the number. Anything that they don't automatically report, you can probably ask through a phone call or e-mail. Once you know the numbers, and then tell us what kind of orchids you are growing, we may be able to tell you if you tap water is a problem or OK for orchids.