Optimizing plant growth through chemistry

Years ago I ran a lot of trials with both a hydroponics system and system that had various types of aquatic life in the water reservoir (aquaponics). Aquaponics is great to minimise your inputs once everything has stabilised, but it does not maximise plant growth, so that is all I will say on that.
Keep in mind that my trials were run in Sydney Australia in a semi outdoor setting.
In the trials that I ran, these were my general findings. My system was run with natural light, not artificial grow light.
Firstly you need to select your medium/watering method.
I found having no medium to have the least maintenance issues and I got the best results in terms of plant health with nutrient film type watering. This is a continuous trickle of water that the roots dangle into. There are many approaches and it is worth a lot of research into this aspect of hydroponics. If you use nutrient film you can only transplant seedlings into the system once their roots are long enough to get access to the water film.
Leafy greens are your best option in terms of plant selection and in general monocotyledons do better than dicotyledons and annuals generally perform better than perennials. There are exceptions though, I got excellent results with strawberries for example.
Plants that do not like humidity tend not to do well, eg tomatoes.
I didn't ever test any growth hormones with the hydroponics, but in the past I have tested the effect of gibberellic acid on plants growing in soil and while the plant growth definitely changed I found no appreciable improvement to yield of the edible plant parts.
For my nutrients I got best results with the following mix
KNO3 - 500 g
CaSO4.2H2O - 400 g
MgSO4.7H2O - 300 g
CaH4P2O8 - 200 g
(NH4)2SO4 - 100 g
FeSO4.7H2O - 5 g
Dissolve all of this in 10 L of water (store it in a 20 L sealed bucket).
Then to start add 150 mL of nutrient solution per 50 L of water in your system.

I choose these chemicals because they were easily available to me. Mix it up as you see fit, but try to keep a similar N:K:SO4:Ca:Mg ratio to the above.
Add a little micronutrient fertiliser when you kick the system off then forget about it until you see symptoms of deficiencies, they are too hard to balance without expensive kit/analysis and uptake rates vary substantially with plant type.
Measure your conductivity when the nutrients first go in and the pH is in the right spot, then top up with your nutrient solution to match that initial conductivity value on a regular basis.
I got best plant growth with pH around 6 as this gives a good balance for a range of nutrient bioavailability. I used sulphuric acid and potassium hydroxide for my pH adjustments once the nutrient was in.
I did not control humidity or temperature in my system so I can't offer you much on that. Nor did I dabble in selective breeding or tissue culture.
Other helpful tips.
- Do a lot of reading on set ups that will work best for you before you invest in infrastructure. A hydroponics set up can be as simple as a single tank that your plants dangle into. There are obviously pros and cons for each methodology. Nutrient film didn't necessarily maximise plant growth for me, it just worked best for the setting and climatic conditions that I had from a maintenance perspective.
- Keep all light away from your reservoir otherwise you will end up with a heap of algae removing nutrients and causing additional maintenance.
- adjust your pH very gradually, calculate what you think you need to add, then add 10 % of that and monitor the pH over the next 30 minutes, once you have done this a few times you will get a feel for your system.

Hope this helps, good luck and have fun!

edit
it should read N to P to K ect I did not intend to insert an emoji

[Edited on 8-10-2020 by B(a)P]

Quote: Originally posted by Tsjerk

What do you mean with hydroponic exactly? With or without inert substrate? Often growing without substrate is referred to as aquaponics. I would advice using an inert substrate, it is easier than completely aquaponic and from what I understand the plants grow faster when on a substrate. Tomatoes are well documented in hydroponic systems, they would be a nice species to start with.