Peat’s Guide to Hydroponics in the AeroGarden
Part 3 – Plant Problems and Nutrients
PLANT NUTRIENTS
Macronutrients – Primary Nutrients
• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)
Macronutrients – Secondary Nutrients
• Calcium (Ca
• Magnesium (Mg)
• Sulphur (S)
Micronutrients – Secondary Nutrients
• Boron (B)
• Chlorine (Cl)
• Cobalt (Co)
• Copper (Cu)
• Manganese (Mn)
• Molybdenum (Mo)
• Silicon (Si)
• Iron (Fe)
• Zinc (Zn)
MOBILE ELEMENTS
These are able to translocate and re-translocate to other areas of the plant.
Mobile elements are more likely to show their deficiencies in the older leaves, during demand
for them these elements will be located to the new growth – this causes the older leaves to
exhibit deficiencies first.
Nitrogen (N) – Mobile Element
Deficiency: Slow, spindly growth, lack of vigour, weak and stunted plant.
Yellowing of leaves (chlorosis) – old leaves first, veins remain green to begin with. The yellowing migrates
through the entire leaf, the leaf will then die and fall off. The stems of the plant and leaf undersides turn a
reddish-purple - this is also indicative of a phosphorous deficiency as well though. Progression of this
deficiency turns the older leaves yellow between the veins which then turn entirely yellow, this spreads
through the plant affecting the more mature leaves then the younger ones in turn, all foliage eventually
drops.
Toxicity: Excessive, lush foliage that is soft and often dark green.
Stems of the plant can become weak and bend over, roots underdeveloped and can become brown/copper
coloured, leaves in bad cases can also turn this shade before drying and falling off, flowers become small
and few. Progression of this toxicity manifests itself in very lush foliage, weakened stems, poor root
development, poor flowers, browning of the leaves which then dry out and drop.
Phosphorus (P) – Mobile Element
Deficiency: Causes dwarfed, stunted growth, delayed flowering, small fruits/buds.
Leaves are smaller than usual and turn a greenish-blue colour and can develop blotches. Stems and the
main veins can turn a reddish-purple colour starting on the leaf undersides, leaf tips of mature leaves turn
dark and curl under. Badly affected leaves show large blackish-purple dead blotches, these change colour
to bronze-purple before drying out, shrivelling, and then dropping off. Progression of the deficiency is
much the same, dark greenish-blue leaves with blotches, the plant is stunted and the blotches then
increase in size before turning bronzish-purple, mutating, and then falling off.
Toxicity: Most plants can tolerate toxicity, however, symptoms will show as zinc, iron, magnesium
calcium and copper deficiencies!
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Potassium (K) – Mobile Element
Deficiency: Older leaves start turning dark yellow, first at the tips then the margins before the entire leaf
is affected, the leaf will then die. Brittle and weakened stems can then arise with the plant becoming more
susceptible to disease. Progression of this deficiency has the plant looking very healthy with dark green
foliage, leaves then lose their lustre, branches are weak and scrawny. Leaf margins can turn grey, then
rusty brown before curling and drying up, older leaves then yellow with rust coloured blotches, leaves curl
and rot with the older leaves then dropping.
Toxicity: Hard to spot as it’s usually accompanied by other deficient nutrients, too much will react with
magnesium, manganese, zinc and iron. Symptoms are the same for those nutrients mentioned.
Magnesium (Mg) – Mobile Element
Deficiency: The lower canopy of the plant develops yellow patches between darker green veins, rusty
brown spots can appear at the leaf margins, tips, and between the veins, the tips of the brown leaves
tend to curl upwards before dying. Progression of this deficiency results in the middle canopy developing
yellow patches between darker green veins with possible rusty spots on the leaves themselves. The brown
spots and yellowing then increase, this spreads from the bottom of the plant to the top, leaves then dry
and die.
Toxicity: Rare and hard to diagnose visually, it conflicts with other nutrients.
Zinc (Zn) – Mobile Element
Deficiency: Younger leaves show interveinal chlorosis, newer leaves and the growing tip develop a small
area that contorts with the leaf wrinkling. The leaf tips followed by the margins discolour and burn,
flowers contort and change shape before turning crispy, dry and hard. Growth will be inhibited all over the
plant, flowers and buds will stop development. Progression of this deficiency occurs in newer leaf growth
developing interveinal chlorosis, new leaves are thin and weak, tips will turn dark brown and die off, new
horizontal growth contorts and plant development halts.
Toxicity: If extremely toxic the plant will die very quickly. Excess zinc interferes with iron which in turn
can cause iron deficiency, sensitive plants will become chlorotic.
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IMMOBILE ELEMENTS
These are not able to re-translocate to other areas of the plant.
Immobile elements will show their first symptoms on younger leaves and progress to the
whole plant.
Calcium (Ca) – Immobile Element
Deficiency: Very green foliage and very slow growth, the youngest leaves show the initial signs. New
growing shoots develop yellowish to even purple hues before disfiguring, shrivelling and dying off. Flower
development is inhibited, the plant becomes stunted and the yield is poor. Progression of the deficiency
causes the younger leaves to become dark green, growth slows, growing shoots discolour, mutate, shrivel
and die. Blossom end rot can occur.
Toxicity: Difficult to diagnose visually, however can cause wilting. May precipitate with sulphur to cause
the nutrient solution to become cloudy, once calcium and sulphur combine they produce gypsum, this is a
residue that settles in the bottom of the nutrient tank. Too much calcium can also lock out potassium,
magnesium, manganese and iron.
Sulphur (S) – Immobile Element
Deficiency: Turns young leaves lime green to yellow, as things progress the leaves yellow interveinally
and lack succulence. Veins remain green, leaf stems and petioles turn a purplish colour, leaf tips burn
then darken before curling down. The deficiency can resemble that of nitrogen, if it continues it can cause
elongated stems to become woody at the base. Progression of this deficiency causes the older leaves to
turn pale green, leaf stems change to a purple colour, then more of the leaves turn a pale green before
yellowing. Interveinal yellowing then happens before then entire leaf system changes to yellow.
Toxicity: Overall smaller plant development, smaller darker green foliage. Leaf tips and margins can
scorch and discolour.
Iron (Fe) – Immobile Element
Deficiency: Only common when pH rises above 6.5, smaller leaves develop interveinal chlorosis with the
veins staying green, the area between the veins turns yellow. Interveinal chlorosis starts at the head of
the leaf and not the tip. As the deficiency increases the chlorosis becomes worse, leaves can drop off.
Progression of the deficiency causes younger leaves and growing shoots to turn pale green, yellow in
between the veins with the veins themselves remaining green. More leaves yellow with the chlorosis
spreading to the older leaves, all leaves will eventually develop necrosis and drop.
Toxicity: Hard to diagnose, can inhibit the uptake of phosphorous. Very high levels cause leaves to turn
bronze and develop small brown and dark leaf spots.
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Manganese (Mn) – Immobile Element
Deficiency: Found first in the younger leaves, these yellow between veins of the leaf. Interveinal
chlorosis occurs with the veins staying green, the problem then migrates to the older leaves once the
younger ones have been affected. Dead spots develop on badly affected leaves before the leave falls
completely. The overall growth of the plant is stunted and the plant can survive beyond it’s maturation.
Progression of the deficiency starts with interveinal chlorosis of the younger leaves before spreading to
the older ones, dead spots increase and the plant remains stunted.
Toxicity: Younger and new leaves become chlorotic and develop dark orange to rusty brown mottled
leaves. Younger leaves suffer first before the problem spreads to the older leaves, plant growth slows and
vigour will decline. Manganese deficiency causes zinc and iron deficiencies .
Boron (B) – Immobile Element
Deficiency: The stem tip and root will mutate, root tips discolour, slow and elongate. Growing shoots
look burnt, the top shoot mutates and burns before lower growing shoots show the same issues.
Progression of the deficiency causes tips to die, leaf margins discolour, necrotic spots develop between
the leaf veins. Roots become soggy and the insides turn mushy which encourages rot, deficient leaves
then become mutated, thicken and wilt with chlorosis and necrosis then gaining a hold.
Toxicity: Leaf tips yellow before progressing to necrotic leaf margins which then become necrotic in the
centre. Leaves will eventually fall off.
Copper (Cu) – Immobile Element
Deficiency: Young leaves and growing tips wilt and become limp, leaf tips and margins then develop
necrosis and turn dark coppery grey. Progression of the deficiency can cause the entire plant to wilt,
growth is slow and the yield reduced.
Toxicity: Overall slowing of the plants progress, interveinal iron chlorosis deficiency, stunted growth,
roots darkening and slow to grow.
Molybdenum (Mo) – Immobile Element
Deficiency: Rare in high energy plants, older and middle aged leaves develop interveinal chlorosis,
leaves continue to yellow and develop rolled margins. Progression of the deficiency leads to mutated
leaves which die and fall off, overall growth of the plant is stunted.
Toxicity: Rare in high energy plants, causes deficiency of copper and iron, causes discolouration of leaves
depending on plant type.
Chloride (Cl) – Immobile Element
Deficiency: Not very common, young leaves can turn pale and wilt though. Progression of the deficiency
causes leaves to become chlorotic, they become bronze in colour. Roots mutate and develop thick tips
and end up stunted.
Toxicity: Younger leaves develop burnt tips and margins, the leaf systems will turn a bronze colour young seedlings are very susceptible to this toxicity. Progression of the toxicity results in burnt tips which
migrate through the whole plant, yellowish bronzed leaves will be prevalent, these will be smaller and
growth retarded.
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Silicon (Si) – Immobile Element
Deficiency: Decreases overall yields and vigour of plant, causes leaves to mutate.
Toxicity: Undetermined.
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