Correct watering does not only consist of mixing water and fertilizers according to the instructions on the label. There is a bit more behind the preparation of a well-rounded diet for our plants than it might seem at first glance.
Plants are capable of creating their own food from inorganic sources available to them. Using energy obtained from light, they convert carbon dioxide and mineral ions into more complex organic compounds.
The plants absorb the carbon dioxide through their leaves with the help of tiny pores called stomata, which at the same time allow the evaporation of excess water from the plant. The evaporated water is replenished by plants from the soil through the roots.
Constant water cycle
The evaporation process – transpiration – is indispensable for the movement of water in plants. The amount of evaporated and absorbed water depends on many factors, although the plants are able to regulate the amount of water absorbed to some extent by means of various refined mechanisms. The main external factors influencing transpiration are temperature, humidity and air movement around the plant, as well as the intensity of light.
The more inorganic substances are in the water, the greater the conductivity of the solution.
The water in the substrate contains not only hydrogen and oxygen molecules but also many mineral ions, which serve the plants as a source of nutrients. Due to the different concentration of minerals in the water inside the plant and around the roots, a phenomenon known as osmosis can occur. Osmosis is a type of passive transport in which a solvent, in this case water, passes through a semipermeable membrane from a space with a less concentrated solution to an environment with a more concentrated solution.
Thanks to the simultaneous action of all these factors and forces, the lant maintains a constant water cycle, and with it a supply of nutrients. The water content in plants is between 60 to 90 percent of their total weight; the plant will perish if the water saturation of its tissue falls below 50 percent.
When watering, you can add specialized fertilizers to the water which can positively affect the plants’ health and the quality of the harvest. When preparing the mixture, you need to pay attention to several rules so as not to disturb the balance of the complex organic system.
Water of life
Before deciding on which cultivation technique you want to use, it might be a good idea to take into account the source of water at your disposal. In general, untreated water from natural sources, such as wells and lakes, and/or rainwater is suitable for growing in soil and other organic substrates. The microorganisms present in such water will contribute to the rich microbial life in the soil and improve the nutrient uptake by the roots.
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On the contrary, growing systems using materials such as mineral wool, perlite and clay pebbles, which are of purely inorganic origin and do not contain any nutrients, are very sensitive to the presence of unwanted microorganisms in the watering solution. For these cultivation methods, it is better to purify natural water using special filters – or choose tap water, but beware of chlorine! See the box above.
Water hardness and EC
In addition to organic impurities, water can also contain inorganic substances, most often various positively charged ions of these substances. These can be beneficial in small amounts for your plants, especially calcium (Ca2+) and magnesium (Mg2+) ions, which are essential for proper plant nutrition.
Conversely, free ions of other substances, such as chlorine (Cl+) and sodium (Na+), have a negative effect on plants. A good example of water not suitable for watering is sea water, which contains a very high amount of chlorine and sodium ions in the form of salt. Increased amounts of calcium and magnesium can be found in underground water sources; these minerals are also added to tap water.
The pH value needs to be measured every time you add fertilizers, because they can often drastically affect the resulting acidity.
Exact determination of all the impurities in the water would require laboratory analysis, but there is a handy solution for home growers: a device called an EC meter, which measures the electrical conductivity (EC) of water or a nutrient solution. The more inorganic substances are in the water, the greater the conductivity of the solution. Distilled water, which is freed of all impurities by filtration, will have an EC value of zero millisiemens (0 mS). Rainwater also has a zero ion content. Water from the tap and water from wells and other natural sources may have a different EC range.
Typical confusions
Growers often mistakenly consider high EC water to be hard, and low EC water to be soft. Water hardness is defined by the amount of dissolved calcium and magnesium ions, without taking into account other impurities that have effect on increasing EC. Needless to say, adequate amounts of calcium and magnesium benefit plants, and growers sometimes even add them to the watering solution.
If your water source has EC values of 0.5 mS and higher, use specialized fertilizers for hard water or consider the purchase of a reverse osmosis filter, which will remove all impurities from the water. If the EC value of your water is higher than 1 mS, water treatment is necessary. However, remember to add magnesium and calcium back to the treated water– or use fertilizers intended for use with distilled water.
Fertilizers and pH
The acidity of fluids is commonly described by pH values, with the number 7 describing the neutral state. For the correct function of plant roots, a slightly acidic environment with a pH of 5.5 to 6.5 is most suitable, depending on the chosen growing medium and the method of irrigation. Litmus papers or an electronic pH meter can be used to measure pH.
The pH value needs to be measured every time you add fertilizers, because they can often drastically affect the resulting acidity of the mixture. It is not good to mix fertilizers and additives from different manufacturers. At first glance, they may appear similar in composition and dosage, but the recipes are different and such an imbalanced mixture could hurt the plants rather than help.
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Before measuring, always let the watering solution rest for 20–30 minutes so that the pH values stabilize, and only then, if necessary, adjust the acidity of the solution. In circulatory systems, where unused watering is returned to the irrigation tank, pH control and maintenance is essential for the success of the entire growing operation.
Watering frequency and the ratio of fertilizers
The frequency and amount of watering varies according to the growing method or system you are using, but in general, several rules apply.
Young plants and clones need a sufficiently moist substrate for the proper development of their root systems but should not be overwatered. At the same time, seedlings are not able to absorb a solution which is too concentrated. Therefore, in the first phase of growth, go for more frequent irrigation with a smaller amount of water and with no or next to no fertilizers.
As the plants gradually grow in size, their leaves are able to evaporate more water, and thus absorb more water from the roots. Their demand on the amount of nutrients also increases, so watering can contain a larger proportion of fertilizers.
As the plants gradually grow in size, their leaves are able to evaporate more water, and thus absorb more water from the roots.
In the flowering phase, plants need a different composition of nutrients, so it is advisable to choose a brand with fertilizers that distinguish between recipes for growth and flowering. As the plants gradually mature and naturally lose their leaves, their ability to transpire also decreases, and they require less fluids.
Many growers strongly believe in the benefits of a simple technique called flushing. In the last few days or weeks, they only water the plants with clean water to rinse away excess minerals and improve the taste of the buds. There have been long-standing disputes among growers over whether this method is really effective.
No matter whether or not you flush, be sure you nourish your plants with care and precision!
Beware of chlorine and chloramine
The trouble with tap water is in the presence of chemical cleansers which are added in public water treatment plants to improve water quality. The most fundamental issue for growers is the presence of chlorine. It not only kills both harmful and beneficial microorganisms but also has a negative effect on root growth and function during long-term exposure. The good news is that chlorine can be removed from water easily, by evaporation (up to 4 or 5 days; UV light, water circulation and aeration will speed the process up) or boiling (6–8 minutes); the bad news is that nowadays it is being replaced by the more stable chloramine. And chloramine can only be removed with the help of a special filter or a chemical dechlorinating agent.
Author: Filip Ostrowski
Source: Cannabis Therapy Vol. 2
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