Phosphorus summary

Phosphorus plays an important role in all living organisms and forms an essential element in plant and animal foodstuffs. It has a key position in cell metabolism and the plant’s total energy transfer. It is also a building block for the cell walls, DNA and all sorts of proteins and enzymes. The availability of phosphate is essential for young plants since approximately three-quarters of the total amount of phosphorus absorbed by the plant occurs before it is a quarter of the way through its life cycle! The biggest concentrations of phosphorus are also found in the self-developing plant parts such as the roots, side shoots and vascular tissue.

Phosphorus is a non-metal, chemical element which, because of its nature, is not found in its pure form because it is extremely reactive. It was discovered in 1669 by an alchemist who was condensing urine in an attempt to make gold. Phosphate compounds are rarely found in nature in the form that plants can utilise. Ground bones (bone meal) were previously used as fertilizer and they were later treated with sulphuric acid which made the phosphates a lot easier to absorb. In the second half of the 19^th century, guano, a natural phosphate fertilizer, was dug up on a large scale and used in farming. These raw materials are currently obtained from rock phosphates which are phosphate rich ores. Some of the locations where this is mined include Morocco, Algeria and North and South America. In order to make rock phosphates suitable for use in agriculture and market gardening they are first acidified and purified. In alternative agriculture they are first finely ground or heated and are then available to the trade as expanded granules.

• In the beginning the plant has a dark green color but it’s a different dark green (blue-green) from that of a K deficiency.

• Growth in height and the development of side shoots are inhibited.

• After 2 to 3 weeks dark purple/black necrotic spots form on the older and middle-aged leaves causing them to deform.

• The purple/black necrosis later spreads out to the leaf stalks. The leaves turn, curl badly and die.

Developments in chronological order:

Symptoms

Certain phosphorus symptoms that are described in the literature should not be confused with a nitrogen deficiency. In cannabis, a phosphorus deficiency is not particularly characterised by striking purple colouration of the stems and leaf stalks, but by a small plant that has purple/black necrotic leaf parts that deform the leaf and cause it to curl up later.

Development:

• In the beginning the plant has a dark green color but it’s a different dark green (blue-green) from that of a K deficiency.

• Growth in height and the development of side shoots are inhibited.

• After 2 to 3 weeks dark purple/black necrotic spots form on the older and middle-aged leaves causing them to deform.

• The purple/black necrosis later spreads out to the leaf stalks. The leaves turn, curl badly and die.

Possible causes of Phosphorus deficiency:

Because phosphate is almost always found in very low concentrations in the environment the affinity of plant cells for phosphate is very considerable and it is absorbed by the entire root.

Deficiencies are therefore quite unusual except for:

• Conditions where the pH is too high (>pH7) in the growing medium. Under these circumstance the plants can barely absorb phosphorous at all and insoluble phosphorus compounds form in the soil.

• If the growing medium is rich in iron or zinc or if it is too acidic.

• Because of soil fixation.

What should you do?

Inorganic phosphates in ion form are absorbed very easily. As far as is known, plants do not absorb phosphorous in its organic form but inorganic phosphates can be released by the decomposition of organic soil particles. Because of the residual effect of phosphate it’s often the case that the older the ground the richer it will be in phosphate. Using fertilizer that contains phosphate, after it has been established that there is a deficiency, often has little effect. This is because hardly any phosphate enters the growing medium due to precipitation or absorption and any growth disorders that occur in the young plant hardly respond at all to repair at a later date. Because of this the phosphate fertilizer should be thoroughly mixed through the soil.

• Prevention is better than cure, use good soil and/or a good fertilizer. Go to your specialist trade shop for expert advice.
• If the pH is too high it is best to use a diluted solution of phosphoric acid to acidify the growing medium. Safe pH values for hydro: 5.2 – 6.2, clay soil: 6 – 7, potting compost and sandy soil: 5.5 – -6.5.
• Alternative fertilizers that contain phosphate include: guano, blood meal, bone meal, rock phosphates, Thomas slag and semi-liquid manure. The disadvantages of these is that their phosphate content varies greatly and absorption is often only moderate. How finely the rock phosphates are ground and acidifying them before use will improve their solubility. It is best to use products where the packaging guarantees certain percentages.

Warning: Excess phosphate damages the environment and can cause all sorts of side effects such as zinc, copper or magnesium deficiencies.

Magnesium is a vital element for humans, plants and animals. Among other things it is a building block for chlorophyll in plants so it is essential for photosynthesis and it also plays an important role in a number of metabolic processes. Magnesium compounds have been used since antiquity in medicine for heartburn, against poisoning and as a laxative. Magnesium powder is used on equipment for gymnastic exercises because it makes the hands rough and absorbs moisture. Magnesium is a very light, malleable, elastic metal with a silver-white sheen that burns with a blinding light in the air. It is one of the most common elements on earth and the earth’s crust contains approx. 2.09% magnesium, but only in compound form. Magnesium compounds are frequently found in seawater, salt deposits, water from salt lakes and in some mineral waters. It is also present in tap water and, together with calcium, is responsible for the hardness of water. Inorganic, magnesium fertilizers are prepared from the same salts as are used when preparing potassium fertilizers. When grown from seeds cannabis don’t need extra nutrients for the first two weeks.

• There are no visible symptoms in the first 3 – 4 weeks, the plant continues to grow well, is dark green and looks healthy.

• The deficiency symptoms first become visible in cannabis after 4 – 6 weeks when small, rust brown necrotic spots and/or cloud-like chlorosis appear under the flowering top on the middle-aged leaves. The color of the young leaves and the development of the flowers remains normal.

• The size and number of the rust brown spots increases on the leaves while the chlorosis also spreads and becomes yellower.

• The symptoms spread throughout the plant which will now look a sorry sight.

• If it is a serious deficiency the young leaves will also become chlorotic and production will fall.

Developments in chronological order:

Symptoms

Magnesium is mobile in the marijuana plant so if there is a deficiency, the chloroplasts in the middle-aged leaves that are below the flowering top are broken down and the magnesium is transported to the young parts. This process of breaking down the chlorophyll is manifested in the rust brown spots and/or vague, cloud-like chlorotic spots between the veins. It is more difficult to extract magnesium from the older leaves because the magnesium is an intrinsic part of the organic material. A minor magnesium deficiency has little effect on flowering despite the fact that the formation of flowers makes the magnesium deficiency symptoms worse.

Development

• There are no visible symptoms in the first 3 – 4 weeks, the plant continues to grow well, is dark green and looks healthy.
  

  

• The deficiency symptoms first become visible in cannabis after 4 – 6 weeks when small, rust brown necrotic spots and/or cloud-like chlorosis appear under the flowering top on the middle-aged leaves. The colour of the young leaves and the development of the flowers is still normal.

• The size and number of the rust brown spots increases on the leaves while the chlorosis also increases and becomes yellower.

• The symptoms spread throughout the plant which will now look a sorry sight.

• If it is a serious deficiency the young leaves will also become chlorotic and production will fall.

Possible causes

Magnesium deficiencies in cannabis occur more often relative to other deficiencies. Magnesium deficiency in the root environment can also occur when magnesium levels are normal or high as well as when there is a deficiency. This is because absorption can be slowed down by all sorts of circumstances.

Some of these are:

• A very wet, cold and/or acidic root environment.

• High levels of potassium, ammonium and/or calcium (for example a lot of lime in the tap water or lime rich, clay ground) compared with the magnesium levels.

• Limited root system and a heavy load on the plants.

• High EC in the medium, inhibited evaporation.

What should you do?

• Use fertilizers that contain magnesium as a preventative measure and spray with Epsom salts as a curative measure.

• Check the temperature, humidity, EC and pH in the soil or substrate.

• Go to the shop for expert advice. They specialize in this crop and have the right products available. Correctly formulated fertilizer contains sufficient magnesium.

• If it has been established that there is a deficiency you should spray with a 2% solution of Epsom salts.

Fertilizing via the roots: Inorganic: Epsom salts on hydro, kieserite on soil. Organic: old, rotten stable or turkey manure.

• Correct possible causes: If the pH is too low (< 5) when cultivating in soil use turkey manure which contains magnesium. With hydro cultivation temporarily drip feed the nutrient solution at a higher pH of 6.5. If the EC is too high rinse and/or drip feed with just tap water temporarily. When cultivating inside keep the root temperature above 19 ?C (20-25 ?C).

A little extra magnesium won’t do any harm and excess magnesium doesn’t occur very often when cultivating with soil. If there is too much magnesium, calcium absorption will slow down and it will look like there is too much salt because growth will slow down and the crop will turn dark green.