We all know that plants basically make their own food using water, carbon dioxide and sunlight, but what is often overlooked is that plants also need a wide range of other nutrients to support healthy growth and prevent diseases. In this post we are going to learn about the primary nutrients that plants need, and how to spot and correct deficiencies.
The Basics: NPK
These three letters, NPK, stand for Nitrogen, Phosphorous and Potassium (Kalium, latin for Potassium). These are the big three macronutrients – the nitrogen is needed for leafy green growth, the Phoshorous for root development and the Potassium for fruit and flowers – a gross oversimplification perhaps – but a lack in one nutrient will correspond to a lack in that kind of growth.
By providing sufficient levels of these Big Three nutrients the plant is not restrained, and is able to perform to the best of its ability.
The specific signs of acute deficiency are detailed below, but inadequate levels of these three basic nutrients can cause lacklustre results, weak growth and few flowers.
These are not needed in as high of a quantity to the three above, but are still required in surprising amounts for strong growth. Magnesium, Sulfur, Iron, and Calcium are all needed in some greater or lesser degree by most plants.
These are needed in tiny quantities but are still very much needed by the plants to some degree, these include Molybdenum, Selenium, Boron, Copper, Cobalt, Nickel, Zinc and Manganese. There are some more, such as silicon, which are helpful to growth but most growers will not notice their absence.
Plants also benefit from certain additives which enhance growth but are not necessary in the strict sense. Examples can include spraying with 2% sugar solution, enzyme, amino acid and vitamin sprays or root drenches – however many of these are entirely unnecessary and can also lead to other problems (in the case of sugar spray).
Proven effective additives however include Humic and Fulvic acids, and Seaweed Extracts which enhance the ability of the plant to take up nutrients and contribute additional trace elements and natural growth regulators. Careful application of PGR’s (Plant Hormones) and natural chemicals like Triacontanol (which is found in Beeswax and Alfalfa) can also boost plant growth, but only when sufficient nutrients are already available.
All plants have evolved to be a part of a rich eco-system and many of them form strong relationships with symbiotic bacteria and fungi which enhance the root-zone surface area and help to fight off pathogenic bacteria, fungi and insects which would otherwise damage the host plant.
It is possible to add various symbiotic ‘mycorrhizal’ fungi and bacteria to the root-zone in the form of granules and soluble additives, however to maintain this micro-ecosystem it is important to not use heavy chemical-based fertilisers which can upset this balance. A rich and balanced organic fertiliser is often best, as it will also contain most of the trace elements in addition to the ‘Big Three’.
Signs of deficiency
Sometimes signs of a deficiency can also be seen when the growing environment is outside of normal parameters. Extreme heat, cold, lack of aeration, and incorrect soil pH can all show symptoms similar to nutrient deficiencies, and can also effectively cause nutrient deficiencies by preventing uptake by the plant – even though the nutrients are present in the soil.
Check the cultural conditions in addition to the nutrient levels. Overfeeding can also cause symptoms that many be mistaken for a deficiency – thus additional feeding will not help in this situation.
Here are some of the common signs of deficiency of particular nutrients:
Nitrogen : Leaves smaller and weak yellowish growth, with the newest growth generally pale (chlorotic). Can be caused by overwatering or immature compost, or simple deficiency.
Phosphorus: Foliage is dark green, but the older leaves becoming yellow between the veins. A purplish blush is often present on leaves and petioles.
Potassium: Yellowing leaf margins, with dead (necrotic) tissue toward the leaf tips and margins. Older foliage can have a mottled appearance.
Calcium: Common deficiency in Tomatoes, causing brown tips to the fruit, especially in Roma varieties. Stem tips may die, tips of younger foliage may also die and curve at the tips.
Magnesium: Interveinal chlorosis on older foliage, but with green veins. Leaf margins can dry up and curl up or down, leaf drop on older foliage.
Sulfur: Chlorosis of new foliage, but shoot keeps growing. Veins are also pale and lighter than the rest of the leaf.
Iron: Growth of new foliage continues, but becomes very pale on new foliage. The veins remain green, but the rest of the leaf is pale (interveinal chlorosis) – some necrotic tissue may be present on leaf tips. Common when pH is too high, this chlorosis can be evident when growing with buffered coir, especially with somewhat alkaline water. Water buffered Coir with 5.5pH water to avoid this problem.
Manganese: New growth looks pretty gross and has necrotic brown mottling over the leaves, with pale foliage and green veins.
Boron : Weak, weird, twisted new growth and death of the growing point. Brown patches of necrotic tissue and unhealthy looking foliage may also feature.
How to fix nutrient deficiencies fast
Sometimes it can be difficult to fix a nutrient deficiency. If it has gone on for too long, the plant may struggle to recover but continue in a zombie-like state for some time before eventually dying.
The fastest method is to start with a foliar feeding spray. Many ‘complete’ soluble fertilisers can be used in this way, at the right concentration (read the LABEL!).
It is better to use a targeted approach if you can identify the specific deficiency. If Magnesium deficiency is determined, this can be easily corrected with a spray of Epsom salts (Magnesium sulfate). If Iron deficiency is determined, then a spray of Iron sulfate will correct the immediate symptoms.
It should be noted that the root cause of the deficiency needs to be found, otherwise the problem will continue as soon as new growth emerges – or before, preventing new growth entirely. So a ‘whole-plant’ approach is needed.
Treat the whole plant – spray the foliage, and then correct the rootzone too.
The soil is usually the source of these nutrients so this will also need to be fixed. Is the pH wrong? Is there too much fresh organic matter? Is it too wet or poorly drained? Are the roots too cold? These factors and others will influence what nutrients are available in the rootzone, and how well the plant is able to absorb them. In some cases, one nutrient will effectively block the absorption of another. Too much iron, and you may create a phosphorous deficiency, for instance. If the pH is too high, Iron becomes locked out and this can be difficult to fix.
Good maintenance is the best prevention of deficiencies. A regular foliar spray with a balanced and complete range of nutrients can be the key to success. Use it at the right concentration, and when the plant is not under heat stress.
Ensuring your soil has a balanced ecosystem, and including humus or humic substances such as leonardite powder can really make a difference. Humic substances are complex organic molecules that result from the breakdown of organic matter. They can be surprisingly large molecules, and act as a buffer and mediator within the rootzone and the plant as a whole. Foliar spray containing fulvic acids can be absorbed by the plant and help nutrient absorption at the root, resulting in stronger growth in even otherwise healthy plants.
The use of seaweed extract is also highly recommended, as it contains a wide range of trace elements as well as other beneficial growth regulators that assist general plant health.
Unfortunately there is no simple, easy fix for all situations. Each plant species has its own requirements, and even within species there can be differences from plant to plant. The best you can do is to be vigilant, and pay attention to what your plants are trying to tell you.