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Plant nutrients

Plants absorb nutrients from the soil that are essential for growth, development, and survival. These nutrients can be divided into primary (or macro), secondary, and micronutrients. Plants take in these nutrients through their roots. Some nutrients may move freely throughout the plant, while others cannot. If a nutrient can be moved, the plant will be able to provide newer parts with nutrients taken from older tissue. When the plant is unable to move nutrients and cannot take up anymore from the soil, a lack or deficiency may develop. When a plant lacks certain nutrients, it may show symptoms such as stunted growth, yellowing, or smaller fruits. However, most of these symptoms are similar to those caused by plant diseases, insects, changes in air circulation or soil, and so on. It is important to check the plants for other causes and to test the soil, before adding more nutrients.


Nitrogen (N) is the most important nutrient for plants. It is found in the soil and helps plants grow (photosynthesis), produce fruit, tissue growth, and helps form proteins and chlorophyll. This nutrient is also an ingredient for plant protoplasm or the living part of the cells.  The plant can move the nitrogen around, providing newer growth with more nitrogen by taking it from older growth. A lack of nitrogen appears as a general yellowing of the plant, less and smaller fruits, leaves may start growing up, and a reduction in growth. Too much nitrogen is unhealthy for the plant as well. When a plant contains too much nitrogen, root growth is stunted, fruits take longer to ripen and they will have a shorter storage life.


Potassium (K) is another primary plant nutrient since it is very important for plant growth and development. Plants require potassium in large amounts for growth and reproduction. Potassium regulates the CO2 uptake by stomata, triggers the activation of enzymes, influences protein, and starch synthesis, affects water uptake and respiration, and is essential for the production of Adenosine Triphosphate (ATP). A potassium deficiency is hard to notice. Signs are found on (older) leaves, such as brown spots or brown veins.


Phosphorus (P) facilitates growth and development. Phosphorus is especially beneficial to plant roots, needed for storage and transfer of energy, division of cells, respiration, and to help the plant convert other nutrients into units for growth. Because phosphorus helps plants develop and grow better, they are more protected from diseases. Plants require phosphorus from seedling to maturity. Phosphorus is an important requirement of genes and plays a role in the transfer of genes from one generation to the next. This plant nutrient is also essential for the production of Adenosine Triphosphate (ATP). When a plant lacks phosphorus, it may take longer to mature and will not grow to its normal size. Shorter plants and darker leaves are symptoms of phosphorus deficiency, as well as bronze coloration under the leaves.


Calcium (Ca) is important for activating enzymes, holding together the cell walls of plants and other cellular activities. Ca makes sure the plant is strong and can stand up straight. Calcium can not move freely through the plant, therefore, when a plant runs out of calcium it can not take from older tissue and move it to newer tissue. Water carries calcium through the plant; when plants get too little water, the plant may not get enough calcium. Symptoms of a calcium deficiency include distorted growth of new tissue, leaf curling, death of root tips, and death of leaf tips. In rare cases, an excess of calcium can lead to the plant not being able to take up any of the other plant nutrients important for its growth. 

Magnesium (Mg) is important for photosynthesis since it enables chlorophyll to absorb light energy needed for this process. This nutrient also facilitates cell division, stabilization of cell membranes, the formation of proteins, respiration, carrying phosphorus in plants, and (phosphate) metabolism. Magnesium can move freely through the plant, moving from older parts to newer tissue. Older and low leaves turning yellow, red, purple, or brown is the first sign of magnesium deficiency. 


Sulfur (S) is important for plant proteins, enzymes, hormones, vitamins, the formation of certain oils, making it a key factor in determining the nutritional value of the plant and its fruit and vegetables. S is also important for nitrogen metabolism, photosynthesis, and helps improve winter hardiness. Sulfur cannot move within a plant, making symptoms of Sulfur deficiency usually show up in younger leaves first. These symptoms include pale green or yellow leaves, stunted growth, and a smaller plant in general.  


Iron (Fe) helps a plant carry important elements through its system, is vital in the production of chlorophyll (and consequently carrying oxygen through the plant and giving the plant its green color), and enzyme functions. Iron deficiency shows up as leaves turning a sickly yellow color. Symptoms of iron deficiency include yellowing of newer leaves, less fruits, dark green veins, brown leaf edges, and death of leaves.


Boron (B) controls the transfer of energy (or sugars) into the growing parts of the plants, helps in seed development, pollination, the formation of cell walls, and the maintenance of membranes. B is especially important for the health and growth of crops. Boron deficiency results in stunted growth, poor pollen vitality, empty pollen grains, reduced number of flowers, and yellowing of lower leaves. 


Zinc (Zn) helps in the formation of chlorophyll, it’s a building block for many enzymes and proteins. It also plays a role in many processes, such as the production of growth hormone and stem elongation. Zn also helps plants withstand cold temperatures. A zinc deficiency is one of the most common nutrient deficiencies and can reduce yield greatly before any visual symptoms appear. Zinc deficiency symptoms include stunted growth, short and narrow veins, brown spots on the leaves, and death of the affected parts. 


Manganese (Me) is important for chlorophyll synthesis, regulates the splitting of water molecules during photosynthesis, regulates carbohydrate metabolism, immobilizes free oxygen radicals, and influences the uptake of other nutrients. Manganese deficiency can appear in the form of a pale green color between leaf veins, brown spots on leaves, or withering leaves. Manganese deficiency affects younger leaves first.


Copper (Cu) plays a key part in the formation of chlorophyll, several enzyme processes, photosynthesis, respiration, and the metabolism of carbohydrates and proteins. A plant cannot move the copper through its system, so when a deficit develops, it will affect newer leaves first. Copper deficiency symptoms include discoloration, the formation of smaller new leaves, spots on the leaves, leaf wilting, pale pink color between veins, and shorter stem lengths. A copper excess can burn root tips and prevent other nutrients from being absorbed by the plant. 


Molybdenum (Mo) is a mineral from which plants need the smallest amount. Mo assists a plant in turning nitrogen into essential compounds, such as amino acids and chlorophyll. Molybdenum is mobile within the plant, so it can move freely from older parts to new tissue. Molybdenum deficiency affects older and middle leaves first. Symptoms of Molybdenum deficiency include leaves turning pale, death of leaves, misshapen leaves, and flowers failing to form.

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Photosynthesis

What is photosynthesis?

Photosynthesis is a process where plants transform photon (light) energy into chemical energy needed for growth. In contrast to most other living creatures, plants use carbon oxide (CO2), along with water, light, and minerals to fuel their growth and energy needs. They convert this into oxygen and organic compounds. You could say that photosynthesis is the most important factor for most life on Earth since without photosynthesis there wouldn’t be oxygen. The light energy is absorbed by a photosynthetic reaction center, a combination of several proteins, pigments, and other compounds that can be found throughout the plant, but mostly in the leaves. Photosynthesis can be described as the following chemical equation:
 

6CO2+12H2O+light -> C6H12O6+6O2+6H2O
 

Where 6 carbon dioxide molecules combine with 12 water molecules and light energy and are then converted into 1 carbohydrate (glucose) molecule and 6 oxygen molecules and 6 water molecules.

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Ultraviolet (UV) light

Ultraviolet (UV) light

Ultraviolet (UV) light falls outside the visible light range, or PAR, between 100 and 400 nanometers. This type of light can be divided into UV-A, UV-B, and UV-C.
 

UVA lies between 320 – 400 nm and is also called Near UV
UVB lies between 290 – 320 nm and is also called Middle UV
UVC lies between 100 – 290 nm and is also called Far UV
 

The correct implementation of Ultraviolet light can have many benefits. Fighting diseases (such as Mildew) and better smelling and tasting produce are among the benefits of UV light. UV light will help initiate and strengthen a plant’s physical and chemical defense mechanisms and antioxidants including terpenoids, alkaloids, lycopene, anthocyanins, trichomes, phenols, quinones, carotenoids, beta-carotene, and glycosides. These compounds protect your plants, since most of them are toxic to insects and disruptive to the DNA of microorganisms found in molds, pathogens, bacteria, and viruses. These antioxidants also influence the physical and nutritional value of plants, making plants more colorful, and taste and smell better! Treating plants with UV light correctly can prevent fungal diseases such as Botrytis (Gray Mold) and Powdery Mildew from further spreading and surviving by up to 99%1, 2.
 

1 Suthaparan, A. & Stensvand, A. Suppression of Powdery Mildew (Podosphaera pannosa) in Greenhouse Roses by Brief Exposure to Supplemental UV-B radiation. Plant Dis. 1653–1660 (2012).
2 Suthaparan, A. et al. Suppression of Powdery Mildews by UV-B: Application Frequency and Timing, Dose, Reflectance, and Automation. Plant Dis. 100, 1643–1650 (2016).

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Different types of grow light

Different types of grow lights

Home and professional growers have used a different variety of light sources that distribute their light differently. And while some are a big fan of HPS lamps, others swear by LEDs. Horticraft Holland thinks LED has many benefits over other types of light sources, which we will discuss in another article. In this article we want you to meet the different types of lamps growers use.
 

High Intensity Discharge (HID) lamps

High Pressure Sodium (HPS) lights are the most common type of supplemental grow light for professional greenhouse growers. HPS lights emit a mix of yellow, orange, and red light, making HPS lamps great for the flowering phase, but not so great for the vegetative phase of your plants. Metal Halide (MH) lights are used with HPS since these emit more blue light and are thus useful for the vegetative phase of the plant. HPS lamps produce a lot of light, but also a lot of heat. The bulbs can reach very high temperatures (as high as 450ºC or 842ºF) and lights should not be placed too close to the crops or anything flammable. HPS bulbs have a lifespan of about 10.000 hours and should be replaced every 12 months.
 

Metal Halide (MH) lights are mostly used during the vegetative phase because MH lamps put out the light in the blue and green range of the spectrum. That’s why you’ll see MH and HPS used in combination, MH will be used during the vegetative stage and when it’s time to flower, the MH bulbs will be replaced by HPS bulbs. Since MH lights are best for the vegetative stage, they are good for growing lettuce and spinach. MH bulbs are filled with a gas mixture of mercury and metal halides (compounds between metals and halogens). To grow with MH bulbs, you will also need a ballast and a reflector. Finding the right ballast is important since it can underpower or overpower the MH bulb. Overpowering the bulb can lead to the bulb exploding. MH lights tend to become very hot and can lead to serious burns of your canopy, but also anything flammable. MH bulbs have a lifespan of around 6.000-15.000 hours and should be replaced every 6-10 months.
 

Ceramic Metal Halide (CMH) lights have a balanced output, since they have a mix of blue, orange and red light. This makes CMH lights more PAR efficient than MH or HPS lights. Though, HPS still have a better red light output than CMH and are better for the flowering stage. The Color Rendering Index (CRI) of CMH bulbs is higher than MH and HPS bulbs, making your plants appear more realistic with CMH lights. This makes it easier to inspect your plants for diseases and pests, but also for their general well-being and growth. CMH lights have a higher initial cost than both MH and HPS lights, although they will prove to be cheaper in the long run. CMH lights put out a lot of heat and should be handled with caution. CMH bulbs have a lifespan of around 20.000-24.000 hours and should be replaced every 2-3 years.
 

Fluorescent lamps

Compact Fluorescent Lighting (CFL) is cheap and suitable for small grow areas or a single plant. They can be found in most hardware stores. These types of light are especially great for beginners. The “soft white” and “daylight” color temperature bulbs are best for gardening. The daylight bulbs are good for the vegetative stage, while the soft white is better for the flowering phase. CFL bulbs put out less heat than HPS bulbs and can be placed closer to the plant, making them well suited for seedlings and young plants or any other kind of low-key indoor gardening. However, the light does not penetrate deep into the canopy, making them less suitable for bigger plants and packed grow areas, and as a consequence giving you lower yields. Since the light from CFL bulbs is mostly pointed away from the plant, using a reflector can be useful to direct all light to your crops. CFL bulbs have a lifespan of around 8.000-15.000 hours and should be replaced every 6-10 months.
 

Light Emitting Diodes (LED)

Light emitting diodes (LED) use a low amount of energy and put out little heat. LED lights are made up of many small diodes and each of these can be customized to put out a specific color wavelength. This means that LEDs can be customized to a full spectrum, making them ideal for every stage of the plant life cycle. LEDs have better penetration than CFL bulbs and their light can be directed better. LEDs produce a lot less heat (usually less than 80ºC or 176ºF) and direct a lot less infra-red radiation towards your plants. Although LED grow lights are the most expensive option, they are far cheaper in the long run, since you will need less climate control, pay less for energy consumption, get higher yields and their lifespan is significantly longer. LEDs have a lifespan of around 50.000 hours and should be replaced every 5 years. 

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What is light

What is light?

Light can be described as electromagnetic energy or waves moving from one point to another. Each wave for a certain wavelength looks the same; it has the same beginning and ending, and the same height and width. Some wavelengths are shorter, meaning faster wave formation, while other wavelengths are longer (slower wave formation).

The whole range of light wavelengths is called the light spectrum. Wavelengths are measured in nanometers (nm), which is equal to one thousand millionths of a meter (10^9). For example, ultraviolet light lies between 100 and 400 nanometers, while red light can be measured around 680 nanometers.

That particular band of light that growers are especially interested in is PAR or Photosynthetically Active Radiation. PAR light lies between the range of 400 and 700 nanometers and is also called “visible light”. Plants use PAR light for photosynthesis or growth.

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PAR, PPF & PPFD

Photosynthetically Active Radiation

PAR stands for Photosynthetically Active Radiation. PAR includes the light ranging from 400 to 700 nanometers that plants use for photosynthesis. The amount of PAR is expressed as the number of micromoles (µmoles) of photons being emitted by the light source.

PAR can be used in determining the strength and overall quality of a grow light. However, it is important to note that the amount of PAR alone is not enough. With a single PAR amount, we still don’t know how much light actually reaches the plant. It is therefore important to also know the position and distance of the light relative to the plant when determining the strength of the light fixture. 

While most plants absorb and use a lot of Blue and Red light, Green gets reflected and this is the reason why most plants look green. This does not mean that plants only need Blue and Red light. Plants use all light wavelengths for different purposes, even light outside of PAR (such as Ultraviolet and Infra-Red light) are useful for plants.


Photosynthetic Photon Flux

PPF is short for Photosynthetic Photon Flux. PPF is measured in micromoles per second, or µmol/s. It expresses the number of photons or total amount of PAR emitted by a light source every second. Photons are small particles that carry the electromagnetic energy of light. The PPF value says something about the total light output that can contribute to photosynthesis.

PPF can be measured with a specialized instrument called an integrating sphere. This instrument looks like a big ball. A ray of light gets shined into the sphere, and the spherical form of the instrument will scatter the light throughout the sphere. A detector inside the sphere measures the total amount of photons emitted by the light. 

PPF does not tell you how much of the light actually lands on the plants, but it says something about how efficient a light is at creating PAR.


Photosynthetic Photon Flux Density

PPFD stands for Photosynthetic Photon Flux Density and measures the amount of PAR light actually arrives at the plant. PPFD is the number of photosynthetically active photons that fall on a given surface each second, expressed in µ/m2/s. PPFD is important when it comes to grow lights, since it measures the amount of usable light that falls on a specific location of your canopy and says something about the true light intensity of the lamp. Light is generally brightest in the center of the canopy and less bright towards the edges of the coverage area, the brightness also decreases the further the light needs to travel. The closer your LED grow lights are to your plants, the more PAR light will actually reach your plants. 

PPFD is a difficult metric to measure consistently, since it depends on many variables. Factors that contribute to PPFD are the distance between the LEDs and the plant and the loss of PPF from the vegetation canopy.

A PPFD chart will show the PPFD values of the grow light for certain points and certain heights in a grow area