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Among professional marijuana growers, osmosis has been a household name for some time, but for many novice growers it may still be a big question mark. So what exactly is that, that osmosis? And how does osmosis work to ensure that cannabis plants can absorb sufficient water and nutrients?
Osmosis is based on the principle that the walls of plant cells allow some substances to pass through, but not others. The cell walls are for that semi (partly) permeable (permeable). An example: when we put a bladder with a sugar solution in a container of water, the bladder will swell. The sugar solution attracts water. The more sugar there is in the solution in the bladder, the more water will be attracted and the higher the pressure in the bladder will rise.
In plants, osmosis ensures, among other things, the firmness of the cells. So much water is absorbed until the plant cells are ‘sucked up’ and the stem and leaves can stand upright. If there is too little water available, the plant cells release the water slowly but surely. The firmness is lost and the plant starts to hang…
Reverse osmosis
A second way to make a plant lose its firmness is to ensure that the osmosis works in the other direction. If the water that is given to the plant contains too high a concentration of substances, the plant will not absorb water, but rather release it and therefore become less firm. An example is adding too high a dose of fertilizer to plants. Over-fertilization will cause plants to dry out and burn…
A second important function of osmosis is the piggybacking of salts (nutrients) with the water that ends up in the plant cells through osmosis. The nutrients are necessary for all kinds of growth processes to take place. Furthermore, the salts ensure that different types of plants develop different properties.
Law of the minimum
In general, plants need the following substances dissolved in water: nitrogen, phosphorus and sulfur to build cells. Magnesium for building chlorophyll (leaf green). Potassium, calcium and magnesium for the osmotic processes. Water for construction, for the transport of nutrients and for strength, and iron, boron, copper, manganese and zinc as building material.
Most plant nutrients are sufficiently present in our ordinary tap water, but not all of them. The law of minimum plays a major role in plant nutrition. The law of the minimum means that the substance present in too small an amount is a limiting factor in the health of the plant. There are so-called deficiency diseases when a plant is deficient in one or more nutrients. For example: a deficiency of iron results in almost completely white leaves.
This plant is clearly deficient in nutrients. Photo: SD_FlowerPower, Shutterstock
In the case of deficiency diseases, it is not only about the direct effect (an unhealthy plant does not grow well), but also about a reduced resistance. If there is a deficiency, the chance of infections by fungi and pests increases. In order to grow plants in a healthy way, we therefore need supplements to the substances that occur naturally in our water. This mainly concerns nitrogen (the abbreviation for the chemical name of nitrogen is: N), phosphorus (abbreviated to: P) and potassium (K). A sophisticated combination of these substances for both the growth and flowering phases is available in grow shops and is becoming a NPK solution named.
carrot hairs
Water and the nutrients (salts) dissolved in it are absorbed through the root hairs of the plant. The condition of the subsoil plays an important role in this. A firm soil gives little space for water to reach the root hairs, a loose soil gives much more space, while rock wool substrates, for example, can guarantee a very good supply of water and nutrients.
The transport of water and nutrients ensures that the substances mainly end up in the leaves. Two forces are responsible for this: the suction of the leaves and the root pressure
The root hairs are therefore very important. When they do not work properly, the plant does not receive enough water and fertilizers. Thus, growth is inhibited. Root hairs are very sensitive, they can be easily damaged by exposure to air and light. Moreover, you destroy them by careless transplanting or by exposing them. The absorption of water and nutrients costs the plant energy, so it needs oxygen and glucose. Finally, temperature is a limiting factor. Even if you provide enough water and nutrients, if the soil temperature is too low, the growth of the plant will be stunted.
Root hairs are super important, but also super delicate. Photo: Dmytro Tyshchenko, Shutterstock
The transport of water and nutrients ensures that the substances mainly end up in the leaves. Two forces are responsible for this: the suction of the leaves (they lose moisture through evaporation, creating suction) and the so-called root pressure. Root pressure can be observed when, for example, we cut off a branch from a tree in the spring. Fluid will then come out of the wound. We call this the bleeding of the plant. The suction power of the leaves depends on the evaporation of water by the leaves. The stomata are responsible for this evaporation process.
CO2 absorption
These stomata can open and close. In addition to evaporating water, they also take care of the absorption of carbon dioxide (CO2) from the air. They also ensure the removal of the oxygen produced. In general, the stomata will be open when it is light (which also ensures CO2 absorption and optimum suction power of the leaves) and closed when it is dark (no CO2 absorption and evaporation is needed).
However, if the air becomes too dry (dry, hot summer afternoons!), the stomata can also close during the day. A clean environment (because of the ‘silting up’ of the stomata) and sufficient potassium (nutrient!) are necessary for the stomata to function properly. And optimal climate control of course!
[Openingsfoto: Eric Limon, Shutterstock.com]
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