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I follow and highly recommend the
following parameters for hydroponic nutrient solutions
for aeroponic, ?bubblers?, drip, ebb and flow, NFT,
passive, rockwool and wick systems.
PH 5.1-5.9
(5.2 optimal)
TDS 500-1000ppm, EC .75-1.5
Temperature 68-78f, 20-25c (75f, 24c optimal)
The pH of the nutrient solution is a major
determinant of nutrient uptake by the plant. If the pH
wanders outside the optimum range of between pH 5.1 and
pH 5.9, then nutritional deficiency and/or toxicity
problems can occur. For hydroponic nutrient solutions
used with inert media, keep the pH at 5.2 for optimal
elemental uptake. It is at this point that roots most
readily assimilate nutrients. These pH and TDS/EC
recommendations may seem low relative to the normally
suggested range, but are based upon information garnered
from "Hydroponic Nutrients" by M. Edward Muckle and
Practical Hydroponics and Greenhouses. They both
document the low pH resulting in increased nutrient
uptake and my experience has shown discernible health
and yield improvements at a ph of 5.2 over higher
levels.
On page 100, Hydroponic Nutrients
displays both the assimilation chart for organic soil
applications and another for inert medium hydroponics,
which depicts the vastly different scenarios (see
below). The widely accepted soil based chart is
frequently misapplied to water culture applications. His
research and that done by others, documented in
Practical Hydroponics and Greenhouses, indicate that
iron and phosphorous precipitate in nutrient solutions
at pH levels above 6. Stay below a pH of 6 by all means
to avoid this problem and benefit.
The nutrient
assimilation rate is further enhanced by the reduction
in solution TDS/EC, which reduces osmotic pressure and
allows the roots to draw the nutrients "easier". Young,
established seedlings or rooted cuttings are started at
500-600ppm. The TDS is increased to 800-900ppm during
peak vegetative growth. During the transition from early
to heavy flowering, TDS is further raised to 1000ppm. It
is then reduced to 400-500ppm during the final 2 weeks
of flushing. The plants demonstrate their preference for
a lower TDS/EC when running a lower pH by clearly
sustaining higher growth rates.
The optimum
temperature for hydroponic solutions to be is 24c/75f.
At this point, most elements are assimilated highest and
atmospheric oxygen is most readily dissolved. Although
increases in temperature increase the rate of
photosynthesis, avoid exceeding the maximum listed of
25c/78f. Elevated temperatures make some elements more
available, but reduce the solution's dissolved oxygen
capacity, increasing root disease likelihood.
Nutrient Availability Chart
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