Fertilizer strength - measurement

[Maru777]

Hello everyone,
Could you help me with some information on fertilizer strength? After playing it by ear since I my plants I finally got a meter that measures the particles in the water based on the water’s conductivity to electricity. However I realized I have no idea what I should be aiming for help! I have some phals, dendrobiums, 2 catts and 2 encyclyas. Tap water reads 80 ppm.

Thank you!

[Ray]

Every fertilizer formula has its own EC-vs-concentration curve, so nobody can tell you "aim for this to get that", except the manufacturer.

I recommend that you consider the following:

1. Decide what nitrogen concentration you want to use.
2. Mix up some fertilizer solution to that concentration as accurately as you can.
3. Using your new toy, measure the EC/TDS and then you can use it as your control device going forward.

As far as what N concentration, I recommend tying that to the frequency you want to feed, with there being a weekly total of 75-100 ppm N. In other words, use that concentration if you feed weekly, half that if you feed twice a week.

As far as measurement, a ppm is a milligram/kilogram, making it 3.785mg/gallon. If your fertilizer is 20% N, then 1 ppm N of that is 5mg/L or 19mg/gal. As it's tough to measure that small amount in the home, you can make a concentrate to start, then dilute that for use.

For example, 100 ppm N of that 20% N fertilizer would be 0.5g/L or 1.9g/gal. If you made a 100x concentrate, 50g/L, , then 10 ml of that, diluted to a liter, would give you your 100 ppm N solution for measurement and use. As I use gallons, I'd go with 128 x 1.9 = 243g, so I could use one ounce of that to make a gallon of final solution.

If you want to take a much simpler approach that's probably good enough, 8/%N on the label = teaspoons/gal for 100 ppm N, or 9.2/%N = ml/L.

[Maru777]

Thank you! This is very helpful! Your explanation is very logical and it helps a lot!

Originally Posted by Ray

[*]Using your new toy, measure the EC/TDS and then you can use it as your control device going forward..

This was pretty much the reason I bought it - I always measured the fertilizer (love toys - obviously - so actually have a nifty scale too) but never had a “check” to see what I ended up with. Was also worried about the water since salts are salts whether I added them or they were already in the water. I am mostly aiming to use it as a sanity check that I am not going to burn the plants.