Cannabis is a fast growing plant species and requires generous amounts of nitrogen throughout growth and early flowering. Nitrogen is regarded as belonging to the group of three primary nutrients essential for plant growth. The other two nutrients in this group are phosphorus and potassium. These will be dealt with here separately. Nitrogen is stored mainly in the leaves and shoot tips,which is why it is inadvisable to remove healthy leaves on plants,as these are the “storage house”for important nutrients. The production of enzymes,proteins,chlorophyll and other vital ingredients for healthy development are all dependent on nitrogen. Chlorophyll lends plants their green color which is why yellowing leaves are a telltale sign of N deficiency.
A serious pest infestation of aphids,white flies,or spider mites that suck out the leaves leads to deficiency symptoms.
Too small container size for adult plants is one of the most common mistakes in cannabis growing. Especially in light intensive situations such as balcony or garden grows the plants will quickly yellow and wilt. Don’t be too lazy and repot your plants. You can do this up to the third week of flowering even.
Poor soil quality. The second major cause for a deficiency. The importance of using quality grade horticultural soil cannot be stressed enough. Do not use topsoil from the forest if you are not certain about it’s nitrogen content. Decomposed leaf material contains no nitrogen (obviously since these are the yellowed leaves shed by the trees!) and makes up for a large percentage of forest topsoil. Also loamy and sandy soil are mainly devoid of important nutrients. If you do utilize such soil in guerilla grows,etc. then make sure to supplement it with long term acting fertilizer,or enrich it with a mix of organic nutrients (bat guano,composted soil,etc.) that have sufficient quantities of nitrogen to support plant growth.
A pH imbalance will block nutrient uptake in the root zone. Make sure that you keep the pH within the acceptable range for soil or hydroponics.
Lack of fertilizing. A minimum of fertilizing on soil is usually necessary to boost plant growth,since cannabis tends to grow faster than the roots can assimilate the natural nutrients in soil. In low light situations or indoors this is less of an issue than in a greenhouse/outdoors/or in a setup using CO2. With high quality soil and a good container size you can probably do without any grow fertilizer if you are cultivating short to medium sized plants.
The lower leaves yellow between the veins until the entire leaf is eventually yellow. It wilts and dies.
The symptoms spread upwards affecting all sun leaves and then the smaller and younger leaves as well.
Plant growth is inhibited. The plants remain short and underdeveloped if nitrogen deficiency is severe in the growth phase.
During flowering early deficiency can lead to a significant decrease in yield. Plants that are in the last 3 weeks of flowering do not require nitrogen if they have remained reasonably healthy up to that point. A yellowing and shedding of leaves during the final weeks of flowering is quite natural among otherwise healthy plants and should not be held up by heroic dosages of nitrogen (which would result in many undesirable complications such as:mold,sudden stop in bud development,dying of pistils,over-fertilization,rejuvenation/leaf growth in buds).
Appearance of male flowers on female plants.
Growers are nowadays so obsessed with yield that a P deficiency has become less common. The market is overflowing with products that supposedly increase bud production. These chemical cocktails and organic wonder mixes are made with high levels of phosphorus. The trend to pump the plants full of a variety of “bud boosters”,often at extremely high dosages (ie. EC levels),is generally of more concern than combating deficiency symptoms! The good news is that cannabis can store large amount of P in it’s shoot and root tips and in the vascular tissue. But still,one should tread the middle path,as with all plant nutrients,and not overfeed the plants.
Phosphorus is required during all stages of plant development – especially during pronounced root and bud growth. It is necessary for photosynthesis and is a component of enzymes and proteins.
Poor soil quality lacking sufficient amounts of phosphorus;loamy or waterlogged soil.
A pH imbalance will block nutrient uptake in the root zone. Make sure that you keep the pH within the acceptable range for soil or hydroponics (between 5.8 and 6.8).
Lack of fertilizing. A minimum of fertilizing on soil is usually necessary to boost plant growth,since cannabis tends to grow faster than the roots can assimilate the natural nutrients in soil. During flowering the phosphorus stored in the plant is gradually used up. Low to medium range dosages of a quality grade fertilizer are sufficient to prevent any serious P deficiency in the peak period of flowering if you cultivating on soil. In hydroponics the plants have a steady supply of readily available nutrients,so it is not necessary to increase EC levels and “force”plants to produce more buds. This can backfire and lead to over-fertilization with all it’s accompanying problems. If you do want to give your plants more P without raising the EC level,then consider adding osmosis water to your tap water to lower the starting EC level. This way you can add some more fertilizer without affecting the regular EC level of the nutrient solution.
Over-fertilization. Too many salts in your medium will cause phosphate to become chemically bound and unavailable to the plants. In hydroponics you can flush the system. But in soil grows this is more of a problem since you will wash out important nutrients and cause the soil to become waterlogged.
In young plants a deficiency slows growth. The plants are underdeveloped with a poor root zone and small bluish-green leaves.
In flowering plants the leaves turn reddish-purple. This generally starts at the leaf tips and spreads towards the leaf stem. Stems may also redden. In acute cases leaves turn necrotic and fall off.
Bud growth and yield will be below average if a deficiency sets in during early to mid-flowering.
Seeded plants will have less well developed seeds.
Lack of vigor and overall lack of mold and pest resistance.
This mineral is the third in the group of primary nutrients required in larger quantities by cannabis. Potassium should be available throughout the plants life cycle. It plays a part in regulating transpiration,the manufacture of starches,sugars and chlorophyll. Potassium is therefore important for the generation of energy within the plant and enhances plant and root growth. All complete fertilizers contain potassium. Kelp or seaweed extracts and composted soil such as worm castings is an excellent organic source. Wood ash contains high levels of potassium but due to the equally high calcium content it also raises the pH and should only be used on acidic soil.
Poor soil quality.
Over-fertilization. Also here the same principles apply as with phosphorus.
A potassium deficiency sometimes resembles lack of nitrogen in the first stages of leaf deterioration. But the difference is that the leaves also develop rust-colored spots. Eventually the affected leaves wilt and drop.
The leaf tips on healthy leaves may turn brown and resemble the symptoms of over-fertilization. This is due to a disruption in transpiration (since potassium regulates the opening and closing of the stomata on the leaf surface,where water evaporates from the plant and gases such as CO2 are drawn in).
In severe cases the stems become brittle.
A deficiency is more common in older plants and therefore the flowering phase will be negatively affected. You can expect low yields.
Magnesium is the fourth most important nutrient and used in larger amounts by cannabis plants. It is also one of the more common deficiencies indoors,due to several factors that can occur which inhibit the uptake or availability of Magnesium. Growers can act preventively by adding dolomite lime to the soil mix or watering/spraying their plants with a solution of Epsom salts. If you have vigorous plants and quality horticultural grade soil with a good pH value (6.0-7.0),then it is unlikely that you will get any Magnesium deficiency in your plants. Also hydroponic setup’s seldom experience Mg deficiency since complete NPK fertilizers offer a sufficient supply of this mineral.
Acidic soil (pH 5.0-5.8).
Cold and water-logged/soggy soil.
Over-fertilization (nutrient blockage especially from high amounts of nitrate,potassium,and calcium).
“Hard”water with high calcium content can bind Magnesium in the soil (mix your tap water with osmosis water).
First indications resemble nitrogen deficiency:the lower to middle leaves yellow between the veins until the entire leaves are eventually yellow.
Rusty spots appear dotted throughout the leaves which distinguishes Mg deficiency from lack of nitrogen.
The leaf edges appear necrotic and curl up.
Some leaves develop a whitish tinge.
Symptoms spread throughout the plant by chronic deficiency.
Over-fertilization is a very common phenomenon in cannabis gardens and the #1 bud killer. We see more damage to flowering and yield through overfeeding than through any other gardening error. One of the main reasons is that the recommended dosages on fertilizers are way too high for the normal uptake of plants. Also growers fail to judge what the true plant requirements are during the grow and can be overzealous in wanting to make their plants grow bigger or better. Most people have fallen prey to the marketing of the agrochemical industry and believe that they need a cupboard full of bottles to grow successfully. The problem is enhanced by the low quality of cannabis genetics on the commercial market as many strains are too weak to grow vigorously by themselves and conditioned to respond to artificial feeding.
Generally speaking it is important to provide your Mandala seedlings/clones with good quality soil and a sufficient container size. This basically takes care of most or all of the nutrient requirements throughout the first 4+ weeks of growth. After this period you should start 12/12 and then repot your females into fresh soil. Bigger containers must be provided if you extend the vegetative time (to raise mother plants for example).
Plants with good genetics are also not dependent on being “force fed”. They develop a good root system and take care of their own needs,as long as they can find what they are looking for in the substrate. Mandala strains belong to this category since they have hybrid vigour and develop very strong shoots,leaves,and root growth. All Mandala strains can be grown indoor without fertilizing (or just minimal feedings) from start to finish if you provide good soil and the correct container size. Fertilize only if you cannot repot on time into fresh soil,if you notice slight deficiency (usually mild nitrogen deficiency shows up after several weeks growth) and need to top up nutrients,or have run into more visible deficiency problems. Large mother plants usually require moderate periodic feedings.
Non-Mandala plants with poor genetics (ie. from too much inbreeding,etc.) will be difficult to handle either way and are finicky:some require higher levels of feeding in hydroponics because they are so inefficient in nutrient uptake;others develop a salt buildup very quickly because they are underdeveloped,weak,and cannot support fast growth.
Check the EC levels of your nutrient solution first and remember that regardless of what is written on the packaging – never feed your plants with more than EC 0.6-0.8 mS/cm (indoor) to 1.0-1.2 mS/cm (outdoor) on soil! This way you will always be on the safe side. For hydroponics consider using lower EC levels (1.0-1.6 mS/cm) and flushing less,instead of heroic dosages that always push the plants to the edge. This is not only more environmentally friendly,healthier,but also means less stress and maintenance problems.
Wait until your plants show slight deficiency symptoms like lack of leaf luster or a slight yellowing of the lowest leaves. There is no point in fertilizing a healthy plant that is lush and green. Why interfere in what nature does best?
When you fertilize give the plants time to assimilate the nutrients and use them for growth. Don’t feed them every day or several times a week. Usually it takes 6-8 days for cannabis plants to fully show the effect of the fertilization if they are growing on soil. After this period of time you can make an assessment if they require a bit more or not. Cannabis grows best if it is fertilized in small portions rather than receiving a big dosage all at once.
(Note:all EC levels indicated are from the Hanna Sharp EC meter and measured in milliSiemens)
- Planting young or flowering plants into a soil mix with high levels of nitrogen.
- Failing to check the EC level of your nutrient solution in soil cultivation. If you don’t check the EC level you have no idea how high the salt concentration is that you are feeding. The EC is also influenced to a large extent by the quality of your tap water. It makes a big difference if you have tap water with an EC of 0.4 or 0.8 mS/cm. Depending on the water you therefore have to adjust the dosage of the fertilizer,so that the nutrient solution does not exceed a certain max. EC level. If the water quality is poor then you should use a household osmosis unit and mix the osmosis water approx. 50/50 with your regular water to reach a low EC starting level.
- Using the full recommended dosage of manufacturers instead of a minimal dosage to test plant response,and to see how many nutrients are really required for healthy growth.
- Fertilizing too often,such as weekly or even more frequently,which causes a build up of salts in the soil. Also the amount you water influences how many salts the substrate/soil soaks up. Never feed your plants on dry soil.
- Starting the feeding cycle too early for young plants,or feeding your plants although they show no signs of lacking any essential nutrients.
- Not topping off your hydroponic reservoir with fresh water when required.
- Working with high EC levels in hydroponics to force growth/flowering,instead of using low to mid-range EC levels and flushing less.
- Using the wrong pH/EC value of your water/nutrient solution which can block the uptake of mineral salts – thereby causing a reverse osmotic effect in the substrate. The high levels of salt pull water out of the root system of your plants. This is why over-fertilization dries up your plants.
The symptoms are quite diverse and many are often mistaken as a nutrient deficiency! This is due to a lack of gardening experience on the part of the grower,and also due to misguided information in some internet sites where uneducated tips abound.
In many cases over-fertilization is particularly caused by an excess of nitrogen. During the growth and pre-floral phase nitrogen toxicity is quite common. Growers tend to water with a complete fertilizer recommended for this phase and these products all contain a medium to high levels of nitrogen. Nitrogen toxicity begins to show through excessive stem elongation and soft tissue. The plants may appear healthy with lush growth until the negative effects start to set in. In flowering plants it can slow down flowering or even bring it to a standstill. Flowering plants may rejuvenate. Most develop leafy buds and an unusually high amount of secondary shoots (depends on cannabis variety) if nitrogen levels are too high during the pre-flowering. The more advanced stages of excess nitrogen are accompanied by necrosis on many leaves. First the leaf tips burn and dry up. Rusty brown spots appear between the veins and eventually the entire leaf turns brown and falls off.
- Bud development is halted and pistils die off suddenly as if they were pollinated.
- Leaf edges curl up (similar to when plants have a “heat stroke”) due to a disruption in their transpiration which cools down the leaf surface. This symptom is especially pronounced in the upper part of the plant close to the light source.
- Leaves discolor and quickly drop off. Some may yellow and wilt beforehand.
- Diverse symptoms appear all at once signaling a multi-nutrient blockage –mainly due to excess salts from macro nutrients (nitrogen,phosphate and potassium).
- Poor root development and stunted growth.
- Plants become susceptible to mold due to a weakened immune system and bloated cell tissue that retains more water (especially with excess of nitrogen). High EC levels are one of the most common causes for Botrytis or grey mold.
- Wilting of seedlings,freshly rooted clones,or young plants. Symptoms resemble lack of watering.
- High male ratio or appearance of male flowers on female plants.
- Bud mold (Botrytis) on flowering plants.
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In this photograph you can see the diverse symptoms of a multi-nutrient blockage. It arises when excess salts in the substrate bind secondary nutrients such as magnesium,iron,zinc,manganese,calcium,manganese and copper. Usually over-fertilizing with potassium and phosphorus,present in high amounts in fertilizers used for blooming such as the potent 13-14 PK products,causes such a nutrient blockage. The leaves develop a checkered appearance of yellow,brown,and white spots with necrotic edges and sometimes also inter-veinal chlorosis (yellowing). Sometimes weak plants or poor genetics are partly to blame.
Symptoms can spread throughout the plant stunting growth and bud development. In such cases the substrate should be flushed thoroughly. Monitor the EC value of the excess water leaching out of the substrate. Continue flushing until it reaches an acceptable level. In soil this is always a difficult situation since you don’t want to complicate matters by water-logging the soil. Flowering plants in the advanced stages of bud development may develop mold if they stand too long in soggy soil. If harvest is near you should simply stop fertilizing and live with the results. Young plants can be flushed more easily and you can also plant them in fresh soil and larger pots to let them recuperate naturally.