Fertilizing rainwater

[Orchid Whisperer]

Roberta - bear in mind that inexpensive pH and TDS meters are really not very accurate. For pH, you are probably better off with either pH test paper or strips, and accepting that pH measured to a half pH unit tells you most of what you need to know. Test kits that are sold in pool or aquarium stores are also OK, similar data precision.

"TDS meters" are actually just estimating TDS from electrical conductivity, run through an estimation algorithm, and cheap meters can produce very questionable data. This is especially true if you are not calibrating to conductivity standards each day, and the meter is not compensating for temperature. Most decent pH and conductivity meters cost over $500, and the cheapest one I've ever seen that I would remotely trust is about $200 (made by Hanna instruments). I am stating this based on a 30+ year history of working in environmental science that includes a lot of water quality measurement. Your water utility's wide swings in TDS on a daily basis may actually be real, and could be related to tidal effects on whatever water supply your city relies on, or other factors such as water usage or influence of upstream effluents entering the water supply.

[Roberta]

I worked for some years in the environmental business too, including water testing for regulatory compliance, so I'm very familiar with the details. The $500 meters are necessary if you're doing testing to verify that customers are meeting regulations in their quarterly reports (and you need to be accurate in the hundredths place) . But for monitoring purposes the cheapies aren't bad. I do calibrate both the pH meter (3 point calibration) and the TDS meter against standard solutions. The pH meter is rock-stable... I check it regularly against the standard buffers and find no need to recalibrate, it's right on for months, over the full range. It varies a little on readings, but for my purposes, I really don't care if it's 7.2 or 7.3... it can certainly tell the difference between 7.2 and 8.1. For the TDS meter, it drifts a little, but not much. One day I tested my water, got an amazing 187... I thought the meter was broken... recalibrated and got 203. It was just a good day... 2 weeks later it was 350 which is more normal for my area. Don't know about where you live, but here the water company has multiple sources and depending on exactly where they're getting the water on any given day, the TDS can be wildly different. Differs by neighborhood too - on a day when it was 250 at my house it was 575 (same meter) at my friend's house 15 miles north - she gets more Colorado River water than I do. It shows on the plants... I get very little in the way of hard water spotting on my plants - watered with city water. In most other communities in my area, everybody's plants have white deposits on leaves unless they use RO... my water isn't great, but it is a lot better than most around here.

Along with TDS, pH is an issue - different nutrients have ideal absorption at different pH, but there's a "sweet spot" somewhere in the 6.2 to 6.5 range. The TDS in my water is mostly calcium carbonate - as calcium bicarbonate, it sits at pH of about 8 to 8.1 and isn't easy to get lower to gain the optimum benefit of fertilizer components. So pH control is very much a part of my fertilizer regimen. (Vinegar is the acid of choice... gentle, easy to control)

[estación seca]

1/4 teaspoon MSU for pure water per gallon of rain.

Prize, shortest message.

[Ray]

Originally Posted by estación seca

1/4 teaspoon MSU for pure water per gallon of rain.

Prize, shortest message.

The "horrors " of dealing with MSU fertilizer are BS. Keep the jar sealed and you have no issues. And as our esteemed colleague mentioned in the message above, it is by far the simplest way to provide everything the plants need when using a pure water supply.

I will also add that the pH of the solutions applied to our plants is actually of not much concern, as their interaction with the potting medium and plant is what determines the pH that the plant endures.

Google "pour through method to determine substrate pH" to learn how to do it and truly know what's what.

I have watered with solutions as acidic as 3, with no issues whatsoever. I have also struggled to make sure that my pH was between 5.5 & 6.5 for plants in S/H culture (where I was incorrect to assume the pH of the solution was the pH of the pot), only to measure high-3's to low-4's in the reservoir a matter of hours later.

[Orchid Whisperer]

Originally Posted by Roberta

I worked for some years in the environmental business too, including water testing for regulatory compliance, so I'm very familiar with the details. The $500 meters are necessary if you're doing testing to verify that customers are meeting regulations in their quarterly reports (and you need to be accurate in the hundredths place) . But for monitoring purposes the cheapies aren't bad. I do calibrate both the pH meter (3 point calibration) and the TDS meter against standard solutions. The pH meter is rock-stable... I check it regularly against the standard buffers and find no need to recalibrate, it's right on for months, over the full range. It varies a little on readings, but for my purposes, I really don't care if it's 7.2 or 7.3... it can certainly tell the difference between 7.2 and 8.1. For the TDS meter, it drifts a little, but not much. One day I tested my water, got an amazing 187... I thought the meter was broken... recalibrated and got 203. It was just a good day... 2 weeks later it was 350 which is more normal for my area. Don't know about where you live, but here the water company has multiple sources and depending on exactly where they're getting the water on any given day, the TDS can be wildly different. Differs by neighborhood too - on a day when it was 250 at my house it was 575 (same meter) at my friend's house 15 miles north - she gets more Colorado River water than I do. It shows on the plants... I get very little in the way of hard water spotting on my plants - watered with city water. In most other communities in my area, everybody's plants have white deposits on leaves unless they use RO... my water isn't great, but it is a lot better than most around here.

Along with TDS, pH is an issue - different nutrients have ideal absorption at different pH, but there's a "sweet spot" somewhere in the 6.2 to 6.5 range. The TDS in my water is mostly calcium carbonate - as calcium bicarbonate, it sits at pH of about 8 to 8.1 and isn't easy to get lower to gain the optimum benefit of fertilizer components. So pH control is very much a part of my fertilizer regimen. (Vinegar is the acid of choice... gentle, easy to control)

The wide variation where you live makes sense. Not only coastal/tidal influences, but on a given say, if you water is coming from surface water, and there is return flow (effluent) from irrigation back to the river, that will make a huge impact. The return flow may not even be at the surface, can be shallow subsurface flow, picking up all kinds of TDS from the soil. I bet your best days are in winter / spring with a high percentage of son melt.

Where I live, TDS is usually so low it is not a concern. TDS in the high double digits to roughly 150 ppm is fairly typical. I don't ever recall it being over 200. There is a spring I know of, not too far away, where TDS as low as 29 ppm has been measured. We have good rainfall and rocks that weather slowly, yield low dissolved solids (granite and gneiss).

[Roberta]

Originally Posted by Orchid Whisperer

The wide variation where you live makes sense. Not only coastal/tidal influences, but on a given say, if you water is coming from surface water, and there is return flow (effluent) from irrigation back to the river, that will make a huge impact. The return flow may not even be at the surface, can be shallow subsurface flow, picking up all kinds of TDS from the soil. I bet your best days are in winter / spring with a high percentage of son melt.

.

Actually, where I live water gets scrounged from various places... southern Calfiornia is basically a desert. So there is good water that comes from the northern part of the state (originating as snow melt), there is seriously awful water from the Colorado river, and some local ground water. Where I live, actually, it's mostly groundwater, some of which is even reclaimed from treated effluent from the sanitation district plant (since you have background in the environmental business, check out GWRS | OCWD), very little is imported. But each local water district has a different mix, and it varies both by location and time. Even the snow melt ends up mineralized, because there are a lot of carbonates around in the local rocks over which it passes before it gets into the system.

[Orchid Whisperer]

Originally Posted by Roberta

Actually, where I live water gets scrounged from various places... southern Calfiornia is basically a desert. So there is good water that comes from the northern part of the state (originating as snow melt), there is seriously awful water from the Colorado river, and some local ground water. Where I live, actually, it's mostly groundwater, some of which is even reclaimed from treated effluent from the sanitation district plant (since you have background in the environmental business, check out GWRS | OCWD), very little is imported. But each local water district has a different mix, and it varies both by location and time. Even the snow melt ends up mineralized, because there are a lot of carbonates around in the local rocks over which it passes before it gets into the system.

Metro Atlanta does a variant of effluent reuse. See: Water Recycling in Clayton County, Georgia | U.S. Climate Resilience Toolkit A company I used to work for had some early involvement with this facility; at that time, the final cleanup went through soil in a forest ecosystem. Both then and now, that highly treated effluent went back to raw supply for drinking water.

[Roberta]

Originally Posted by Orchid Whisperer

Metro Atlanta does a variant of effluent reuse. See: Water Recycling in Clayton County, Georgia | U.S. Climate Resilience Toolkit A company I used to work for had some early involvement with this facility; at that time, the final cleanup went through soil in a forest ecosystem. Both then and now, that highly treated effluent went back to raw supply for drinking water.

Putting back into the ground instead of directly into the raw water system is political not scientific... It should be used directly, but to sell "toilet to tap" they had to go the circuitous route. (There's not a drop of water on the planet that hasn't been recycled thousands of times but there are a lot of irrational people) I could solve my whole problem with a 3 mile hose to the outflow of that plant... nothing bigger than an H2O molecule is in the water, then they remineralize it so that it doesn't corrode the pipes. They won't let me do that <sigh>