@rmoltis try to get me a close up shot of those yellowing leaves. Are they showing signs of Fe chlorosis? the leaf will be yellow but the interveinals structure will stay green. We can go from there once you can confirm.
Reason I ask is Fe is an essential nute and it can get locked out if the rootzone ph is too high 7.0 and up or it can lock out your Fe if there is too much phosphorus in your grow medium. Take a good close up pic of those yellowing leaves plz and post.
PS keep in mind Fe deficiency is often confused with Mg (Magnesium) deficiencies as well.
Here is some info on Fe
Iron (Fe) deficiency is a plant disorder also known as "lime-induced
chlorosis". It can be confused with
manganese deficiency. A deficiency in the soil is rare but
iron can be unavailable for absorption if
soil pH is not between about 5 and 6.5.
[1] A common problem is excessive alkalinity of the soil (the pH is above 6.5). Also, iron deficiency can develop if the soil is too waterlogged or has been overfertilised. Elements like calcium, zinc, manganese, phosphorus, or copper can tie up iron if they are present in high amounts.
[1]
Iron is needed to produce
chlorophyll, hence its deficiency causes
chlorosis. For example, iron is used in the
active site of
glutamyl-tRNA reductase, an enzyme needed for the formation of
5-Aminolevulinic acid which is a
precursor of
heme and
chlorophyll.
[2]
And here some data on Mg
Magnesium (Mg) deficiency is a detrimental plant disorder that occurs most often in strongly acidic, light, sandy soils, where magnesium can be easily leached away.
Magnesium is an essential micro nutrient found from 0.2-0.4% dry matter and is necessary for normal plant growth.
[1]
A plant with Magnesium deficiency
Excess
potassium, generally due to fertilizers, further aggravates the stress from the magnesium deficiency,
[2] as does
aluminium toxicity.
[3]
Magnesium has an important role in
photosynthesis because it forms the central atom of
chlorophyll.
[1]Therefore, without sufficient amounts of magnesium, plants begin to degrade the chlorophyll in the old leaves. This causes the main symptom of magnesium deficiency,
chlorosis, or yellowing between leaf veins, which stay green, giving the leaves a marbled appearance. Due to magnesium’s mobile nature, the plant will first break down chlorophyll in older leaves and transport the Mg to younger leaves which have greater photosynthetic needs. Therefore, the first sign of magnesium deficiency is the chlorosis of old leaves which progresses to the young leaves as the deficiency continues.
[4]Magnesium also is a necessary activator for many critical enzymes, including ribulosbiphosphate carboxylase (
RuBisCO) and
phosphoenolpyruvate carboxylase (PEPC), both essential enzymes in
carbon fixation. Thus low amounts of Mg lead to a decrease in photosynthetic and enzymatic activity within the plants. Magnesium is also crucial in stabilizing
ribosome structures, hence, a lack of magnesium causes
depolymerization of ribosomes leading to pre-mature aging of the plant.
[1] After prolonged magnesium deficiency,
necrosis and dropping of older leaves occurs. Plants deficient in magnesium also produce smaller, woodier fruits.
