20-18-38 is much higher than organic fertilizers are going to be straight out of the package. It is a percentage composition by weight, so you can't make the number higher. Plus it's not usually 100% soluble, either.

Good fertilization is giving the plant what it needs when it can use it. Similar to aquaponics, organic setups tend to be able to accomplish the same result with much lower NPK numbers than chemical fertilizers. You can also use supplements such as beneficial bacteria/fungi and fulvic or humic acid products, which increase the plant's ability to take up nutrients.

I'm aware that the NPK values don't really correspond when comparing the two. I guess, being very new to gardening, how do you know when too much organic fertilizer is too much and when too little is too little? When there is no way to covert the numbers. There are so many products out there saying you need this and you need that. Then almost 100% of the products I've looked at, don't actually have the exact ingredients on the label. You would think they would be required to do so.....I know guano's have different NPK depending on where you get it and who supplies it. But even if the company puts the NPK on the package they rarely put what else is in it. Very confusing stuff....I may just use water and sunlight LOL!

What makes organics easier is that beyond not having to use as much fertilizer, it is also much more forgiving if you do use too much.

Common measurements like NPK and ppm are only small parts of a much larger picture of the plant's overall health and environment. It's not as simple as there being one perfect number, which is good news, because it means that you don't have to worry so much. Just make your best guess, go with that, and then make your later decisions based upon what your plants are telling you about their health.

â¢Posted by Cole_Robbie none (My Page) on
Sun, Mar 31, 13 at 16:31

"What makes organics easier is that beyond not having to use as much fertilizer, it is also much more forgiving if you do use too much. "

Not only can plants not even tell the difference so organics will NOT grow any healthier of plants, but you can not regulate them as well.

"One of the drawbacks of organic crop production vs. standard hydroponic fertilizer is that the majority of nutrients are not immediately available to the plant. This makes it very difficult to monitor and regulate concentration and ratios of elements available to the plant. If using premium hydroponic fertilizers, the vast majority of nutrients are immediately available in precise and measurable values. As a result, healthy vigorous plants can reach their genetic potential which includes characteristics such as taste and flavor. Plants do not differentiate the nutrients they absorb resulting from hydroponic or organic nutrient solutions. For example, nitrogen is typically available as NO3- or NH4+. It does not matter to the plant whether it came from guano or bottled nutrient. "

I didn't say it was better, just easier. There are plenty of pre-mixed organic hydro nutes on the market.

My larger point is that nutrient solutions are not a precise control of everything about the plant. There's a lot more going on than PPMs and PHs. Those are like the dash gauges on a car. They have value, but there is more to driving than just staring at the gauges.

Your right. I noticed having good compost in my potting mix acts as a good ph buffer. You cant get any better than that.

This should answer your question.

Here is a link that might be useful: Hydroponic Fertilizer : What I Use & How to Mix It

"Here is a link that might be useful: Hydroponic Fertilizer : What I Use & How to Mix It"

That may be useful, although the guy mixing it adds that he is better at counting tomatoes than doing fertilizers.

Better just stick with this to get your NPK:
If you are using an all-in-one 20-18-38 fertilizer and you wish to replace it with an organic fertilizer, just take the *weight* (whether liquid or solid) of the fertilizer you seek to match and get an equivalent weight of the organic fertilizer as follows:

for N:

if you use say 10 grams of N=20 and your organic is N=8, you will need 2.5 times the weight of the organic fertilizer. This is because the organic is only has 40% (8/20) the amount of nitrogen.

Do the same with the phosphate and potash.

For example if I have an organic fertilizer with (A) 5-0-4 rating and another with (B) 0-3-2

and I want close to 10 grams of 20-18-38, I will need 4 times A plus 6 times (B). The result will be:

40 grams of (A) plus 60 grams of (B) which will give the equivalent of 5*4-3*6-(4*4+2*6) which is 20-18-28.

It doesn't give the exact K of 20-18-38, but it gives the same nitrogen and as a bonus P as well. If you were concerned about the K you might try 50 grams of (A) plus 70 grams of (B) instead which would make 25-21-34 if I did the multiplication right.

getting exactly the 20-18-38 is not really possible as you can see but you can get things pretty close. The important thing is to get an organic fertilizer which has a guaranteed analysis. Cole has already mentioned that plenty of other factors are in play and the organic may be less or in some case more bioavailable, so it isn't as much a degree in chemistry as attention to detail and being and experienced cook which means you've had practice testing the limits of what you can put in the broth and still have it be good.

You don't need a degree in Chemistry, just basic Algebra.

I think the biggest problem comes from using Imperial units instead of metric units. Ppm is just mg/L. If you want a N level of 100ppm and the fertilizer is 20-0-0 (just making that up for clarity) you would add 500mg to 1 liter of water. Remember that 20 is just percentage by weight.

I agree nil. I started using metric way back when I started doing hydro and it makes life so much easier.
well and peoples insistence on using a "scoop" rather than shelling out $10 for a digital scale. Using a scale is just as easy as a scoop and waaaayyyy more accurate.
I got a kitchen scale several years ago and now I weigh just about everything when preparing food (and coffee). It makes for much more consistent results.

Right, whether you are preparing plant food or people food all you need is a spreadsheet and a scale!

I am new to hydroponics myself, but I am using the 20-18-38 also. I am trying this formula for now. 12 grams of 20-18-38 and 6 grams of Epson salt per 5 gal of water. Hope this helps..

Rick, the OP is not asking for the fertilizer you mention and was probably experienced with the fertilizer you are currently using and mention, so he probably has the information you posted in his own interpretation of the proper mix ratios.

His question was how to calculate the nutrient levels and proportions of whatever organic nutes he was finding to replace an inorganic salt derived one such as you have with an alternative organically derived fertilizer with similar nutritional properties for the plant, so that he can grow with equal success using a more organically derived nutrient solution.

Hope that helps also & good luck with yours!

WHY don't you let organic.gardening answer...........

Messaging them yourself onmember pages is a private option if you want to dictate who can or can't post.