Heath Robinson on Nutrients
I will go into detail about nutrient concentrations because it seems to be an area which a lot of growers don't fully understand.
I have seen quite a lot of bad advice from experienced growers who advise to "increase the nutrient concentrations until you see tip burn and then back off slightly" I will try explain why this is bad advice.
Nutrient salts can cause harm to plants if they are in high enough concentration in water or soil. This effect is mainly indirect by pulling moisture out of roots and reducing the uptake of water and nutrients to affected plants. This is the cause of tip and edge burn of leaves, if the nutrient concentration was maintained, slow growth, nutrient deficiencies, wilting and eventual death of the plant would occur if the problem is not corrected.
This is the reason why, Water movement in plants is a factor of osmotic pressure and capillary action. Osmotic pressure is defined as water flowing through a permeable membrane in the direction of higher salt concentrations. Water will continue to flow in the direction of the highest salt concentration until the salts have been diluted to the point that the concentrations on both sides of the membrane are equal.
A good example of this is pouring salt on a slug or snail, the salt concentration outside the slug is highest, which causes the water from inside the slug's body to cross the skin membrane. The slug becomes dehydrated and dies.
For osmosis to occur, water must move from a more dilute (the nutrient solution) to a more concentrated compartment (the plant). If you were to water your plant with sea water the plant would wither and die as the salt water now extracts water from the plant instead of replenishing it. So basically high levels of salinity will lead to high concentrations of salt in the plant tissues which will severely damage metabolic processes.
here is a grow chart which will help explain why there is no advantage to feeding your plants high nutrient concentrations.
notice on the chart that there is a deficient zone where the plant is not meeting its needs and growth is poor. A low zone where the plant is growing but lacks all the necessary nutrients to sustain good growth and yield.
Now the important part, you will notice if you look at the sufficient and high zones that there is no advantage to feeding your plants at higher concentrations than is needed. Notice also that growth and yield suffers sharply once the plant is over fertilised. If you feed your plant until it is toxic and showing signs of tip burn and you back off slightly you are still in the excess zone and your yields will suffer to some degree.
I have found that the sufficient zone for
marijuana is in the range from an Ec of 1.0 to 1.6 I personally run in at an EC of approx 1.2 and never exceed 1.4
I hope that helps explain why I do what I do.
