by Ed Rosenthal
General Discussion
Most planting mediums have adequate amounts of Ca. However, Ca should be added to the planting mix if the pH is too low.
Planting mix and hydroponically grown plants are most likely to suffer Ca deficiency. Some hydro fertilizers contain only small amounts of Ca, as the amount of Ca dissolved in the supply water varies. If the water contains more than 150 parts per million (ppm) dissolved solids, it is probably providing the plants with enough Ca. If the water contains less than 150 ppm of dissolved solids, Ca-Mg has to be added to the water to bring it up to 150 ppm. To find out how hard or soft your water is, you will need to have a TDS/ppm meter or refer to the local water district quality report.
COPPER (CU)
Copper (Cu) deficiencies are rare.
Symptoms
Copper (Cu) deficiency first appears in young leaves which exhibit necrosis and coppery, bluish or gray with metallic sheen coloring at the tips and margins. The young leaves turn yellow between the veins.
Other symptoms include limp leaves that turn under at the edges and eventually die, and wilting of the whole plant. New growth has difficulty opening. Flowers do not mature or open in males and in females the stigmas don’t grow properly.
Cu toxicity is rare but fatal. As the plant approaches death, its leaves yellow from its inability to use Iron (Fe). The roots are abnormally sized, then start to decay.
Cu has a low mobility.
Role in plant nutrition
Cu is essential to healthy plant production, reproduction and maturity, and assists in carbohydrate metabolism and oxygen reduction.
Problem Solving
Foliar feeding with copper fungicides such as copper sulfate (CuSO4) and chelated copper adjusts a deficiency. Any hydroponic micronutrient formula containing copper helps as well. Compost, greensand, and kelp concentrates are good natural sources.
Though it vaguely resembles nitrogen toxicity, the yellow-white leaf bottoms and brown and dying fan leaf tips confirm the copper deficiency.
Soaking dimes or quarters in water and then using the water to irrigate the plants also supplies copper, since these coins are 92% copper and 8% zinc. (Pennies contain mostly zinc, not copper.) An acid solution such as lemon juice or vinegar dissolves the copper faster.
General Discussion
Copper (Cu) deficiencies are often confused with over-fertilization.
IRON (FE)
Iron (Fe) deficiency occasionally occurs outdoors, in planting mediums, and in hydro.
Symptoms
Fe deficiency starts in the new leaves, which lack chlorophyll but have no necrotic spots. This causes them to turn bright yellow except for the veins, which remain green. New leaves start to experience chlorotic molting, first near the base of the leaflets so the middle of the leaf appears to have a brown mark. The veins remain dark green. Note that a Fe deficiency looks similar to a Mg deficiency except for its location. Fe deficiency affects the new growth but not the lower leaves while Mg deficiency affects the middle and lower leaves first. Fe moves slowly in the plant.
Role in plant nutrition
Fe is necessary for enzymes to function and acts as a catalyst for the synthesis of chlorophyll. Young actively growing tissues need Fe to thrive.
Problem Solving
An Fe deficiency may indicate a pH imbalance. Adjust pH if out of range.
Iron deficiency. Photo: Anonymous
Foliar feed with Fe chelated fertilizer containing Fe, Zn, and Mn, since these deficiencies are often found in combination. Other Fe-bearing supplements include compost, Fe chelates (often found in hydroponic micronutrient supplements), iron oxides (Fe2O3, FeO), and iron sulfate (FeSO4) for fast absorption. Supplements should be added both foliarly and to the planting medium. Adding rusty water also works.
General Discussion
An Fe deficiency is often found in combination with Zn and Mn deficiencies.
MAGNESIUM (MG)
Magnesium (Mg) deficiency is common in all mediums and hydro. It is not common outdoors.
Symptoms
Mg deficiency starts in the lower leaves. The veins remain green while the rest of the leaf turns yellow, exhibiting chlorosis. The leaves eventually curl up, and then die. The edges of affected leaves feel dry and crispy. As the deficiency continues it moves from lower leaves to the middle to upper half. Eventually the growing shoots change from a pale green to white color. The deficiency is quite apparent in the upper leaves. At the same time, the stems and petioles turn purple. Mg is mobile.
Magnesium deficiency apparent in right plant, contrasted with the green healthy plant on left.
Role in plant nutrition
Mg helps support healthy veins and maintains leaf production and structure. It’s required for chlorophyll production and enzyme breakdowns.
Problem Solving
Water-soluble nutrients containing Mg fix the deficiency. Such nutrients are Mg sulfate (MgSO4, Epsom salts) and Ca-Mg for fast absorption; and dolomite lime/garden lime and worm castings for moderate absorption.
In hydro and planting mixes Mg deficiencies are easily fixed using 1 teaspoon (4.9cc) of Epsom salts per gallon (1.3cc per liter) of water in reservoirs. In planting mixes use 1 teaspoon per quart (5cc per liter) of water in planting mixes. After the first treatment, use one-quarter dose with each watering or change of reservoir. Ca-Mg can also be used.
For fastest action Epsom salts can be used foliarly at the rate of 1 teaspoon per gallon (1.3cc per liter). Ca-Mg can be used foliarly as directed.
Dolomitic limestone contains large amounts of Mg. It can be used to raise the pH of soils and planting mixes and supply Mg at the same time.
General Discussion
Mg deficiency is one of the easiest nutrient deficiencies to diagnose and cure. It occurs more frequently if using distilled, reverse osmosis water and tap water that has low ppm count.
MANGANESE (MN)
Manganese (Mn) deficiency is rare and almost always associated with Fe-Zinc deficiencies.
Symptoms
Mn deficiency is generally found in the young leaves. The leaf tissues turn yellow and small areas of tan/brown dead tissue (necrotic areas) appear in the middle of the leaf. The leaf veins usually stay green. The leaf becomes outlined in a ring of dark green along its margins. Too much Mn in the soil causes an Iron (Fe) deficiency. In addition the plant shows a lack of vigor. Mn is not mobile.
Role in plant nutrition
Mn helps enzymes break down for chlorophyll and photosynthesis production, and it aids in making nitrates available for protein production.
Manganese deficiency. Photo: Anonymous
Problem Solving
For fast relief foliar feed with a water-soluble fertilizer high in Mn such as Fe-Zn-Mn fertilizer, hydro micros, or Mn chelate. Then add the fertilizers to the water/nutrient mix. Compost and greensand also contain Mn but they are absorbed more slowly than the water-solubles.
MOLYBDENUM (MO)
Molybdenum (Mo) deficiency is very rare, but is more likely to occur in color-changing strains in cold temperature conditions.
Symptoms
The middle leaves turn yellow. As the deficiency progresses towards the shoots the new leaves become distorted or twisted. A Mo deficiency causes leaves to have a pale, fringed, and scorched look, along with retarded or strange-looking leaf growth. Older chlorotic leaves experience rolled margins, stunted growth and red tips that move inward toward the middle of the leaves.
Sometimes Mo deficiency is misdiagnosed as a N deficiency. However, N affects the bottom leaves first. Mo affects leaves in the middle of the plant first and then moves up to the newer growth.
Excessive Mo in cannabis looks like Fe or Cu deficiency. Mo is mobile.
Role in plant nutrition
Mo is contained in enzymes that help plants convert nitrates to ammonia, which is required for protein production.
Problem Solving
Foliar spraying with water-soluble fertilizers aids in over
coming the deficiency. Because plants need Mo in such small amounts a hydroponic micronutrient mix is often the most efficient way of supplying it. These fertilizers can be used as foliar sprays or applied to the soil, as well as their customary use in hydroponic nutrient solutions.
General Discussion
Molybdenum deficiency late flowering. Photo: Anonymous
Generally a Mo deficiency occurs when S and P are deficient. Mo toxicity does not tend to wreak havoc on plants, but excess intake causes severe problems in humans so extra precautions should be taken when using it.
NITROGEN (N)
Nitrogen (N) deficiency is the most commonly occurring nutrient deficiency in cannabis.
Symptoms
Lower leaves first appear pale green. The leaves then yellow and die as the N travels to support new growth. Eventually the deficiency travels up the plant until only the new growth is green, leaving the lowest leaves to yellow and wither. Lower leaves die from the leaf tips inward.
Other symptoms include smaller leaves, slow growth and a sparse profile. The stems and petioles turn a red/purple tinge.
Too much N causes a lush dark green growth that is more susceptible to insects and disease. The stalks become brittle and break from lack of flexibility.
N can travel anywhere on the plant. Usually deficiency starts on the lower of the plant; because N travels to new growth.
Role in plant nutrition
N is directly responsible for the production of chlorophyll and amino acids, and it is essential to photosynthesis. It is an essential element of tissue; without it growth quickly stops.
Any water-soluble N (especially nitrates, NO3) is quickly available to the roots. Insoluble N (such as urea) needs to be broken down by microbes in the soil before the roots can absorb it. After fertilization, N-deficient plants absorb N as soon as it is available and start to change from pale to a healthy-looking Kelly green. Deficient plants usually recover in about a week, but the most-affected leaves do not recover.
Nitrogen deficiency. Photo: TheNewGuy
N is the first number of the three number set found on all fertilizer packages, which list N-P-K, always in that order. Any water-soluble fertilizer much higher in N than P and K can be used to solve N deficiencies very quickly. Most hydro “Vegetative Formulas” fall into this category.
Ca(NO3) is water-soluble and fast acting. It can be used as a foliar fertilizer and in the water/nutrient solution.
Urine, fish emulsion (5-1-1) high-nitrogen bat or seabird guano also act quickly. In soils high-N fertilizers such as alfalfa and cottonseed meals, manure, feather meal and fishmeal all supply N fairly quickly.
General Discussion
Without high amounts of N, especially during the vegetative growth stage, the plant’s yield is greatly reduced. Water uptake slows from vascular breakdown in the plants. N issues happen throughout the entire growth cycle. Plants should never experience an N deficiency during vegetative growth. However, over-fertilizing with N causes problems too.
Tapering off the use of N towards flowering promotes flowering rather than vegetative growth. However, a small amount of N is always necessary in order for the plant to manufacture amino acids, which use N as an ingredient. This supports flower growth and utilization of P and K. Some “Bloom Boosters” have N-P-K ratios of “0-50-30.” While high numbers sound impressive, using this fertilizer too early causes the flowers to be smaller than they could have been. If there is not enough residual N available, the plants are not getting the most out of the fertilizer.
In the middle to the end of the flowering stage, plants frequently show a N deficiency. They’re using the nutrients that were stored in the leaves and dropping the their oldest, bottom fan leaves. To prevent the deficiency from getting extreme, switch over to bloom nutrients gradually unless the bloom fertilizer contains some N.
PHOSPHORUS (P)
Phosphorus (P) deficiency is uncommon.
Symptoms
P is the second number found on fertilizer packages. They are always listed in the order N-P-K. Plants deficient in phosphorus grow slowly and are stunted with small leaves. The older leaves are affected first. First the leaves turn dark green and become weak. The leaves develop dull blue or purple hues. The edges of the leaves turn tan/brown and curl downward as the deficiency works its way inward. Fan leaves turn dark green with a purple or dull blue hue. The lower leaves turn yellow and die.
Phosphorous deficiency. Photo: Senseless
The stems and petioles turn purple or red. Some strains, however, normally possess red or purple stems and petioles, so these traits are not a surefire sign of P deficiency.
Plants use high amounts of P during flowering. If they don’t get adequate or even abundant supplies, it results in lower yields. P is mobile.
Potassium deficiency: day 21. Photo: Senseless
P aids in root and stem growth, influences the vigor of the plant, and helps seedlings germinate. P is extremely important in the reproductive stages and flowering.
Problem Solving
P is the second number of the three number ratio listed on fertilizer packages. Water-soluble fertilizers containing high P fix the deficiency. Bloom fertilizers are high P formulas. High-P guano also provides readily available P. Rock phosphate and greensand are also high in P and gradually release it. The affected leaves do not show recovery, but no additional growth is affected and new growth appears healthy.
General Discussion
Deficiency during flowering results in lower yields, but over fertilizing can result in “chemical buds” or burn the plant. Cold weather (below 50° F/10° C) can make P absorption very troublesome. For this reason soluble P such as found in water-soluble bloom formulas can add flower yield in cool weather.
POTASSIUM (K)
Potassium (K) is the third number found on fertilizer packages, always listed in the order N-P-K. Potassium (K) defi-ciency occurs occasionally in both planting mediums and outdoors in soil, but rarely in hydroponics. Plants often suffer from mild K deficiencies, even in rich, well-fertilized soil, usually caused by improper fertilization. Many organic fertilizers such as guano, fish emulsion, alfalfa, cottonseed and blood meals, and many animal manures contain minor amounts of K relative to N and P.
Symptoms
Plants suffering from minor deficiencies look vigorous, even taller than the rest of the population, but the tips and edges of their bottom leaves die or turn tan/brown and develop necrotic spots.
As the deficiency gets more severe the leaves develop chlorotic spots. Mottled patches of red and yellow appear between the veins, which remain green, accompanied by red stems and petioles. More severe deficiencies result in slower growth, especially when plants are in the vegetative stage. Severe K shortages cause leaves to grow smaller than usual.
Larger fan leaves have some dead patches, or necrosis, on their margins. These leaves eventually turn brown and die off. Plants with K deficiencies tend to be the tallest.
Excess K causes fan leaves to show a light to dark yellow or white color between the veins. K is mobile.
Silicon and potassium work together to build stronger plant cell walls. This creates a barrier against insects and fungi. Dyna-Gro Pro-TeKt provides silicon which increases the plants ability to tolerate drought and heat as well as strengthen the overall plant.
Role in plant nutrition
K is found in the whole plant. It is necessary for all activities having to do with water transportation, as well as all stages of growth; it’s especially important in the development of buds. K aids in creating sturdy and thick stems, disease resistance, water respiration, and photosynthesis.
Problem Solving
Although symptoms of minor K deficiency affect the cosmetic look of the plant, it does not seem to affect plant growth or yields.
Water-soluble fertilizers containing high K fix the deficiency. Bloom fertilizer usually contains high K levels. It is used in the formulas to balance the pH. Highly alkaline K is used to bala
nce acidic P. Wood ashes deliver K quickly.
Liquefied kelp, bloom fertilizers and wood ash are commonly used and work quickly to correct K deficiencies, as does potassium bicarbonate (KHCO3), potassium sulfate (K2SO4) and potassium dihydrogen phosphate (KH2PO4). Potassium silicate (K2SiO3) can be used to supply silicon and has 3% K in it. Granite dust and greensand take more time to get to the plant and are not usually used to correct deficiencies, but to prevent them.
Damaged leaves never recover, but the plant shows recovery in four to five days with applications of fast-acting products.
General Discussion
Cold weather slows K absorption, as does too much Ca or NH4+. High levels of Na displace K.
SILICON (SI)
Siicon (Si) deficiency is very rare.
Si has not been proven to be necessary for plant growth. However, the presence of Si promotes the development of strong leaves, stems and roots. It also increases resistance to fungal and bacterial diseases and insect infestation. The plant also exhibits an increase in photosynthetic activity and overall yield increases. Si is not mobile.
Si helps the plant overcome different stresses that occur and helps to protect the plant from pests and diseases. It aids in growth, development, yield and disease resistance. It is used to strengthen stem and branch structure.
Problem Solving
Diatomaceous earth can be added to the planting mix. The Si is dissolved by acids into a form the roots can absorb.
Liquid Si is found in Si supplements. It is immediately available to the plants.
General Discussion
Si is abundant in nature, but it is not included in hydroponic fertilizers, so it should be used as a supplement.
SULFUR (S)
Sulphur (S) deficiency is rare.