RELATIVE HUMIDITY The term ‘relative humidity’ (RH) refers to the amount of water vapor in the air and is usually expressed as a percentage (e.g. 50% RH). This can have a major impact on how cannabis plants grow. Low humidity means less water in the air and results in increased evaporation and water use. Excessive humidity comes with its own problems, including creating an ideal environment for pests, mildew, and mold to grow. One key factor related to humidity that is often left out of the conversation is vapor-pressure deficit (VPD) – the difference between the maximum water vapor the air can hold at a given temperature and RH. Although not all growers measure VPD, it significantly influences stomata activity and is directly related with transpiration rate and metabolism. A VPD that is too high means drier air and increased evaporation and transpiration. Too low a VPD can lead to slowed transpiration and reduced growth. Since slowed transpiration reduces nutrient uptake, both too high and too low of a VPD may appear as nutrient deficiencies. It is VPD that drives transpiration and nutrient uptake in plants; the uptake of water at the roots is determined by the loss of water through the shoots, and the loss of water through the shoots is determined by how much water is in the air. Humidity levels influence the rate of water evaporation from the leaves of cannabis plants, which directly affects the tension and suction created within the plant. Higher humidity levels can reduce the rate of evaporation, potentially impacting the negative pressure and water transport efficiency within the plant. CARBON-e DIOXIDE Carbon dioxide is essential for photosynthesis. Light energy is used to convert CO2 and H2O into sugar and oxygen. As the CO2 concentration increases, the rate of photosynthesis increases until a saturation point where no more CO2 can be absorbed. The guard cells (stomata) previously mentioned are specialized to regulate gas exchange, working to optimize the movement of oxygen, water, and CO2 in and out of the shoots. Plants cultivated outside typically don’t need supplemental CO2 (because nature knows what it’s doing). Indoor growers however, may find themselves needing additional carbon dioxide to maximize yields and improve plant growth and development. Without fresh air for plants to exchange oxygen for carbon dioxide, the CO2 concentrations can become low, hindering photosynthesis and dramatically reducing plant growth. Although CO2 is a naturally occurring gas that both humans and plants use, it is invisible and odorless and can be fatal at high-levels. If you’re supplementing carbon dioxide in your grow room, ensure there are no leaks in any CO2 devices and always use a CO2 monitor and alarm. 0.02% Life unsustainable 0.03% Life OK 0.04% Current ambient atmospheric co2 0.04%-0.1% =400-1000ppm standard indoor co2. 0.1%-0.2% =1000-2000ppm (prolonged exposure drowsiness). 0.2%-0.4% = 2000-4000ppm (Headaches, fatigue, stagnant, stuffiness, poor concentration, loss of focus, increased heart rate, nausea). 1% is toxic 5% quick death. AIRFLOW Outdoor plants are constantly exposed to natural elements, and that includes wind. Airflow ventilation is one of the often-forgotten environmental factors in healthy cannabis growth and development. Like all environmental factors, we want to “recreate” beneficial stressors that the plant would be exposed to outdoors. Like human bone that becomes stronger in response to stress from resistance we call exercise, stems increase in rigidity and structural integrity in response to stress from air flow. Plants that lack airflow are prone to developing weak stems, leaving them tall, skinny, and unable to hold bud weight as the plant grows. Excessive air flow, on the other hand, which constantly bends the entire plant, could lead to stunted growth or even broken shoots. Thankfully, you don’t need a wind sensor to achieve optimal air flow; a light breeze that just makes the leaves wave or dance gently can assist in the development of strong, dense shoots. A little too much though can stress so be careful not to overdo it too hard for too long as it will eventually stress. Stagnant air within the grow space can also increase the risk of pests, mold, and mildew. Some pests hide under leaves, along stems, and even in the soil itself. A small fan providing a gentle breeze is often enough to prevent a stationary environment, build stem strength, and reduce the chance of pests or pathogens. Proper air circulation and CO2 exchange facilitated by negative pressure contribute to stronger and healthier plants. Good air flow with constant fresh air is essential for maximizing the growth and yield of your indoor plants.. To achieve and maintain negative pressure in your grow tent, several key factors and components come into play. Understanding how these elements work together is essential for creating negative pressure inside your grow tent.Start by selecting an exhaust fan with an appropriate CFM (cubic feet per minute) rating for your specific grow tent size. The CFM rating determines the amount of air the fan can move per minute, and it’s crucial to choose a fan that can sufficiently exchange the air within the tent to create negative pressure. Install the exhaust fan at the highest point in the grow tent to effectively remove warm and stale air from the space. Mounting the fan near the top allows it to expel the warm air, which naturally rises.The negative pressure then automatically draws in fresh air from the lower intake points. Depending on the size and airflow requirements of your grow tent, consider adding a lower intake fan to facilitate controlled air exchange. An intake fan can help regulate the inflow of fresh air and contribute to maintaining balanced pressure within the tent. Want the exhaust higher CFM than lower Intakes, this is what will give us a negative pressure The passive air intake point in the lower portion of the tent allows fresh air to enter passively. Properly positioned and sized passive intake openings ensure a steady flow of fresh air, contributing to the creation of negative pressure when combined with the exhaust fan’s airflow. Co2's density is such gravity pulls it to the bottom 2-3 inches of any enclosure. Adjust passive intake accordingly, and be as close to the floor as possible. I use a 4" intake passive injecting co2 rich air through the 100 gallon, this pours CO2-dense air around plants in a rough 360 degrees arc from a central point, when the main exhaust kicks in and negative pressure goes from the lower intakes will draw air through the rootzones, oxygenation of rootzones, wicking moisture. Keeping RH 40%-45% on exhaust keeping air on the dryer side, now that the plant is big that fan is never off at night but it keeps that air with lots of space for more moisture from the plant and more moisture from the soil. The faster you can cycle water, more nutrients you can uptake. Slight negative pressure is good for maximizing the yield of a growth regime. It makes it easier to control the temperature, humidity, CO2 levels, and other contaminants of the tent. Well, too much of everything is always bad. And the same does for negative pressure as well. So, how would you understand whether the negative pressure exceeded the limit? The simple trick is- if the tent itself seems to pull itself inwards, the negative pressure is still under the tolerable limit. If the pressure gets as high as it bends the poles inwards, that’s where the danger limit starts. So, if you see the poles bend inwards, the negative pressure is something to worry about. Otherwise, if it’s the tent itself if pulled inwards slightly, you don’t have to worry about it. The cohesion-tension theory explains how negative pressure enables water movement from the roots to the leaves of a cannabis plant. As water evaporates from the leaf surfaces through stomata, tension is created, generating a suction force that pulls water upwards through the xylem vessels. This process relies on the cohesive forces between water molecules, forming a continuous column for efficient water transport. In cannabis plants, xylem vessels serve as the conduits for water transport. These specialized cells form interconnected channels that allow water to move upwards from the roots to the leaves. The negative pressure generated through the cohesion-tension mechanism helps drive the water flow within the xylem vessels. Negative pressure facilitates the movement of water from the soil, through the roots, and up to the leaves of cannabis plants. It helps maintain proper hydration and turgor pressure, ensuring the cells remain firm and upright. This is crucial for healthy growth and structural support. Negative pressure transports water and aids in the uptake and transport of dissolved nutrients within the cannabis plant. As water is pulled up through the xylem vessels, essential nutrients and minerals are transported along with it, supplying the various tissues and organs where they are needed for optimal growth and development. ROOTS OXYGEN As well as releasing oxygen created during photosynthesis, plants need to absorb oxygen to perform respiration – i.e. to make energy. Since plant roots are non-photosynthetic tissues that can’t produce oxygen, they get it from air pockets in the soil or grow medium. These air pockets can vary in size based on the makeup of the growing medium, and also on the water saturation levels of the medium. Root oxygenation and soil aeration play an important role in both transpiration and cellular respiration in all plants. This means that plants are highly dependent on the growing medium that holds the optimal amount of oxygen within. Make sure not to overwater, as roots in compacted soil or fully submerged in water with low O2 can cause irreversible damage if left unchecked. This is why even when growing hydroponically, when the roots are submerged in water, it’s important to have an air pump to incorporate adequate O2 to the roots. Grow mediums like coco coir and soils that contain perlite promote aeration and are less prone to overwatering. TEMPS Whether it’s sunlight outdoors or artificial lights indoors, when light heats the air temperature, soil temperature also rises. But it’s not only the air that influences the soil temperature; the grow medium, plant depth, and moisture level can also change how well the soil releases or retains heat. Not all growers monitor soil temperature, but roots are the reservoir system of water and nutrients, and if they are the wrong temperature, things can deteriorate quickly for any plant. Roots are a living part of the plant and therefore have an optimal temperature range in which they thrive at water and nutrient uptake. Although every plant varies, root temperatures above 88°F & below 55°F (above 31°C and below 12°C) can result in stunted growth and ultimately plant death if exposed for too long. 73-76, Avoid going over 77F as common bacterial growth explodes above 77, if disease strikes it's going to strike 10x faster above 77F. WATER Water is one of the most important factors of cannabis growth and development; both transpiration and photosynthesis involve water. Irregular watering can lead to irregular plant growth and development. Too little water and your plant can become dry, brittle, and stressed. Too much water and your plant’s roots can be deprived of important oxygen, and even drown. One of water’s most important purposes is the transportation and movement of nutrients and minerals, which are typically absorbed in the roots and distributed throughout the rest of the plant. The faster the plant can rid itself of water through transpiration the faster it can uptake more water to get more nutrients to where they need to be, by creating a negative pressure we optimize turgor pressure increasing nutrient uptake, by sticking to VPD we optimize transpiration rate and maximize stomatal openings, with sound frequency we open them further. NUTRIENTS Plant growth and development depends on nutrients derived from the soil or air, or supplemented through fertilizer. There are eighteen essential elements for plant nutrition, each with their own functions in the plant, levels of requirement, and characteristics. Nutrient requirements generally increase with the growth of plants, and deficiencies or excesses of nutrients can damage plants by slowing or inhibiting growth and reducing yield. Many deficiencies can be recognized by observing plant leaves. When most people hear the word “fertilizer” they think of synthetic fertilizers, but the word fertilizer refers to any substance or mixture added to soil or a growing medium that increases its fertility or ability to sustain life. Some fertilizers are synthetically produced, and others are mixtures of decomposed organic waste such as worm castings or bat guano (aka bat poop), which are rich in essential nutrients. Plants require eighteen elements found in nature to properly grow and develop. Some of these elements are utilized within the physical plant structure, namely carbon (C), hydrogen (H), and oxygen (O). These elements, obtained from the air (CO2) and water (H2O), are the basis for carbohydrates such as sugars and starch, which provide the strength of cell walls, stems, and leaves, and are also sources of energy for the plant and organisms that consume the plant. Elements used in large quantities by the plant are termed macronutrients, which can be further defined as primary or secondary. The primary nutrients include nitrogen (N), phosphorus (P), and potassium (K). These elements contribute to plant nutrient content, the function of plant enzymes and biochemical processes, and the integrity of plant cells. Deficiency of these nutrients contributes to reduced plant growth, health, and yield; thus they are the three most important nutrients supplied by fertilizers. The secondary nutrients include calcium (Ca), magnesium (Mg), and sulfur (S). The final essential elements are used in small quantities by the plant, but nevertheless are necessary for plant survival. These micronutrients include iron (Fe), boron (B), copper (Cu), chlorine (Cl), Manganese (Mn), molybdenum (Mo), zinc (Zn), cobalt (Co), and nickel (Ni). 18 elements essential for plant nutrition, and classify the essential elements as macronutrients or micronutrients. Macronutrients: used in large quantities by the plant Structural nutrients: C, H, O Primary nutrients: N, P, K Secondary nutrients: Ca, Mg, S Micronutrients: used in small quantities by the plant Fe, B, Cu, Cl, Mn, Mo, Zn, Co, Ni Nitrogen: found in chlorophyll, nucleic acids, and amino acids; component of protein and enzymes. Phosphorus: an essential component of DNA, RNA, and phospholipids, which play critical roles in cell membranes; also plays a major role in the energy system (ATP) of plants. Potassium: plays a major role in the metabolism of the plant, and is involved in photosynthesis, drought tolerance, improved winter hardiness, and protein synthesis. Nitrogen availability limits the productivity of most cropping systems in the US. It is a component of chlorophyll, so when nitrogen is insufficient, leaves will take on a yellow (chlorotic) appearance down the middle of the leaf. New plant growth will be reduced as well and may appear red or red-brown. Because of its essential role in amino acids and proteins, deficient plants and grains will have low protein content. Nitrogen excess results in extremely dark green leaves, and promotes vegetative plant growth. This growth, particularly of grains, may exceed the plant's ability to hold itself upright, and increased lodging is observed. Nitrogen is mobile both in the soil and in the plant, which affects its application and management, as discussed later. Phosphorus is another essential macronutrient whose deficiency is a major consideration in cropping systems. It is an essential part of the components of DNA and RNA, and is involved in cell membrane function and integrity. It is also a component of the ATP system, the "energy currency" of plants and animals. Phosphorus deficiency is seen as purple or reddish discolorations of plant leaves, and is accompanied by poor growth of the plant and roots, reduced yield and early fruit drop, and delayed maturity. Phosphorus excess can also present problems, though it is not as common. Excess P can induce a zinc deficiency through biochemical interactions. Phosphorus is generally immobile in the soil, which influences its application methods, and is somewhat mobile in plants. Potassium is the third most commonly supplemented macronutrient. It has important functions in plant metabolism, is part of the regulation of water loss, and is necessary for adaptations to stress (such as drought and cold). Plants that are deficient in potassium may exhibit reductions in yield before any visible symptoms are noticed. These symptoms include yellowing of the margins and veins and crinkling or rolling of the leaves. An excess, meanwhile, will result in reduced plant uptake of magnesium, due to chemical interactions. The mobility of a nutrient in the soil determines how much can be lost due to leaching or runoff. The mobility of a nutrient in the plant determines where deficiency symptoms show up. Nutrients that are mobile in the plant will move to new growth areas, so the deficiency symptoms will first show up in older leaves. Nutrients that are not mobile in the plant will not move to new growth areas, so deficiency symptoms will first show up in the new growth. Nutrient mobility varies among the essential elements and represents an important consideration when planning fertilizer applications. For instance, NO3- nitrogen is very mobile in the soil, and will leach easily. Excessive or improper application increases the risk of water contamination. Meanwhile, phosphorus is relatively immobile in the soil and is thus less likely to runoff. At the same time, it is also less available to plants, as it cannot "migrate" easily through the soil profile. Thus, P is often banded close to seeds to make sure it can be reached by starting roots. Nutrients also have variable degrees of mobility in the plant, which influences where deficiency symptoms appear. For nutrients like nitrogen, phosphorus, and potassium, which are mobile in the plant, deficiency symptoms will appear in older leaves. As new leaves develop, they will take the nutrients from the old leaves and use them to grow. The old leaves are then left without enough nutrients, and display the symptoms. The opposite is true of immobile nutrients like calcium; the new leaves will have symptoms first because they cannot take nutrients from the old leaves, and there is not enough in the soil for their needs. In general, plant nutrient needs start low while the plants are young and small, increase rapidly through vegetative growth, and then decrease again around the time of reproductive development (i.e., silking and tasseling). While absolute nutrient requirements may be low for young plants, they often require or benefit from high levels in the soil around them. The nutrient status of the early seedlings will affect the overall plant development and yield. Plants entering the reproductive stages have high nutrient requirements, but many of these are satisfied by redistributing nutrients from the vegetative parts. Nitrogen: nitrate (NO3-) and ammonium (NH4+) Phosphorus: phosphate (HPO42- and H2PO4-) Potassium: K+ Calcium: Ca2+ Magnesium: Mg2+ Sulfur: sulfate (SO4-)