What Is Agar: Using Agar As A Growing Medium For Plants

What Is Agar: Using Agar As A Growing Medium For Plants

By: Bonnie L. Grant, Certified Urban Agriculturist

Botanists often use agar to produce plants in sterile conditions. Using a sterilized medium such containing agar allows them to control the introduction of any diseases while rapidly accelerating growth. Other items are also added to the agar to give new plants vitamins and sugar and sometimes hormones or antibiotics.

What is Agar?

You may remember agar from your high school biology class. It can be used to grow viruses, bacteria, and even plants. This nutrient rich material actually comes from a species of algae. It is transparent, which allows the grower to view the roots of new plants. Agar is also used in some foods, fabric, and in cosmetics.

Agar has been part of scientific study for decades, if not longer. The material comes from red algae, which have been harvest in areas such as California and eastern Asia. The algae is boiled and then cooled to a thick paste. Agar as a growing medium is more useful than cooking gelatin but has a similar consistency.

It is not eaten by bacteria, which makes it more stable than regular gelatin. There are many different types of agar but plain nutrient agar is the one that doesn’t grow a particular bacteria. This makes it a good base medium for germinating plants with agar. In a comparison of agar and soil, agar reduces bacterial introductions while soil may actually favor certain bacteria.

Why Use Agar as a Growing Medium?

Instead of soil, using agar for plant growing creates a more hygienic medium. The differences between agar and soil are vast, but the biggest are that agar is semi-solid, making it easy with which to work and necessary ingredients such as nutrients and vitamins can be added in exacting amounts.

It is also transportable and you can work with very small tissue samples. Agar has been found useful for orchid culture and other specialized plant reproduction in sterile conditions. As an added bonus, germinating plants with agar produces very rapid growth as compared to soil starting.

Using Agar for Plant Growth

You can purchase agar powder for plants at many online retailers. You simply boil water and add the amount recommended and stir it well. The mixture needs to cool to at least 122 degrees Fahrenheit (50 C.) until it can be safely handled. The material will gel at 100 Fahrenheit (38 C.), so have sterile containers ready to pour in the cooling medium.

In about 10 minutes, the agar is solid and should be covered to prevent introduction of pathogens and foreign material. Tweezers of pipettes are useful for transferring the seed or tissue to the prepared agar. Cover the container again with a clear lid and place in a brightly lit, warm area for most plants. Germination varies by species but is generally twice as fast as other germination methods.

Several companies are already developing containerized agar as a growing medium for plants. It may even become the wave of the future.

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400”>Orchids are one of the most popular flowering plants the world over. Their popularity is certainly not unconnected to their eminently beautiful blooms, exotic appearance and the wide spectrum of fragrances they give off.

With over 30000 species and a possible 200000 plus number of hybrids, the inherent diversity of orchids cannot be questioned.

As a matter of fact, orchids species outnumber bird species at a ratio of over two to one.

With such large numbers, it is therefore not surprising that orchids have been found naturally growing in almost all possible habitats known to man including the tropics, temperate zones and even parts of the Arctic circle.

The greater proportion of orchids though are found growing in the tropics. Again, with such large numbers, there is certainly an orchid suitable for every collector, whether beginner or expert, and for every location, whether indoors on a window sill or outdoors in a garden.

To further underscore the availability of an orchid plant for every flower-loving person, they can be purchased for as little as $15. Popular orchid species include Phalaenopsis (which is arguably the most popular), Cattleya, Oncidium, Dendrobium, Vanda, Vanilla, Brassavola, Cymbidium, Miltonia and a host of others.

Types of Mushrooms to Grow

You have many options when it comes to types of mushrooms you grow. Growing only one type means that you typically have fewer complications and you can figure out the perfect environmental conditions for that type. Experimenting with multiple types lets you figure out what works best for you.

Blue Oysters

Blue oysters are an easy-to-grow variety and do well outdoors or on straw logs indoors. They’re a well-known mushroom, but you can’t typically find them in the grocery store, so they can fetch a decent price. They’re an ideal option for a beginner because they’re forgiving.

They have a mild flavor and tender consistency that lends well to cooking.

King Oysters

King oyster mushrooms are another easy to grow option, but they do best when grown in supplemented sawdust rather than straw. They are a bit more challenging to grow blue oysters. The flavor is worth it, though. King oysters have a rich, meaty flavor.

They have a long shelf life you can sell them up to two weeks after properly harvesting. However, since they have a long shelf life, that also means they can be shipped long distances. You’ll face competition from overseas growers.


Let’s be clear up front: chanterelles are not easy to grow. They’re more for the farmer who is looking for a challenge or has some space to play around and see what they can produce. But if you can get them to sprout, you’ll have no shortage of buyers.

Lion’s Mane

Lion’s mane mushrooms will set you apart because most consumers can’t find these beautiful fungi. You can harvest and deliver straight to the customer, but you do need to be careful because they have delicate teeth.

Lion’s mane is delicious, with a buttery, lobster-like flavor, and growing it will produce huge yields.

Wine Cap

Wine cap is a great option if you’re looking for a mushroom you can grow in the soil outdoors. It has a lovely red cap that looks good in your display and the nutty flavor makes it a favorite with buyers.


Shiitake mushrooms are a perennial favorite with buyers, but they are a bit harder for new growers. If you can figure out how to grow them, there’s a high demand out there. They’re well-known and well-liked, so selling your mushrooms won’t be a problem.

What Does It Mean To “Fix” Nitrogen?

When it comes to getting nitrogen from the air to the soil, some plants have special superman powers. These nitrogen-fixing plants use the bacteria to take nitrogen gas from the air and put it in their roots.

In particular, plants like legumes such as peas and beans are particularly adept at fixing nitrogen into the soil. That means they leave nitrogen in their roots behind in the ground. Most plants only uptake nutrients, but legumes kindly leave something behind.

This has an immediate benefit to the plants that are growing, but best of all, it helps nourish the next crop planted in the same location.


  • 1 History
  • 2 Etymology
  • 3 Composition
  • 4 Uses
    • 4.1 Culinary
      • 4.1.1 Asian culinary
      • 4.1.2 Other culinary
    • 4.2 Microbiology
      • 4.2.1 Motility assays
    • 4.3 Plant biology
    • 4.4 Other uses
  • 5 See also
  • 6 References
  • 7 External links

Agar may have been discovered in Japan in 1658 by Mino Tarōzaemon ( 美濃 太郎左衞門 ), an innkeeper in current Fushimi-ku, Kyoto who, according to legend, was said to have discarded surplus seaweed soup (Tokoroten) and noticed that it gelled later after a winter night's freezing. [7] Over the following centuries, agar became a common gelling agent in several Southeast Asian cuisines. [8]

Agar was first subjected to chemical analysis in 1859 by the French chemist Anselme Payen, who had obtained agar from the marine algae Gelidium corneum. [9]

Beginning in the late 19th century, agar began to be used as a solid medium for growing various microbes. Agar was first described for use in microbiology in 1882 by the German microbiologist Walther Hesse, an assistant working in Robert Koch's laboratory, on the suggestion of his wife Fanny Hesse. [10] [11] Agar quickly supplanted gelatin as the base of microbiological media, due to its higher melting temperature, allowing microbes to be grown at higher temperatures without the media liquefying. [12]

With its newfound use in microbiology, agar production quickly increased. This production centered on Japan, which produced most of the world's agar until World War II. [13] However, with the outbreak of World War II, many nations were forced to establish domestic agar industries in order to continue microbiological research. [13] Around the time of World War II, approximately 2,500 tons of agar were produced annually. [13] By the mid-1970s, production worldwide had increased dramatically to approximately 10,000 tons each year. [13] Since then, production of agar has fluctuated due to unstable and sometimes over-utilized seaweed populations. [14]

The word "agar" comes from agar-agar, the Malay name for red algae (Gigartina, Gracilaria) from which the jelly is produced. [15] It is also known as Kanten (Japanese: 寒天 ) (from the phrase kan-zarashi tokoroten ( 寒曬心太 ) or “cold-exposed agar”), Japanese isinglass, China grass, Ceylon moss or Jaffna moss. [16] Gracilaria lichenoides is specifically referred to as agal-agal or Ceylon agar. [17]

Agar consists of a mixture of two polysaccharides: agarose and agaropectin, with agarose making up about 70% of the mixture. [18] Agarose is a linear polymer, made up of repeating units of agarobiose, a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. [19] Agaropectin is a heterogeneous mixture of smaller molecules that occur in lesser amounts, and is made up of alternating units of D-galactose and L-galactose heavily modified with acidic side-groups, such as sulfate and pyruvate. [20] [18] [19]

Agar exhibits hysteresis, melting at 85 °C (358 K, 185 °F) and solidifying from 32–40 °C (305–313 K, 90–104 °F). [21] This property lends a suitable balance between easy melting and good gel stability at relatively high temperatures. Since many scientific applications require incubation at temperatures close to human body temperature (37 °C), agar is more appropriate than other solidifying agents that melt at this temperature, such as gelatin.

Culinary Edit

Agar-agar is a natural vegetable gelatin counterpart. It is white and semi-translucent when sold in packages as washed and dried strips or in powdered form. It can be used to make jellies, puddings, and custards. When making jelly, it is boiled in water until the solids dissolve. Sweetener, flavoring, coloring, fruits and or vegetables are then added, and the liquid is poured into molds to be served as desserts and vegetable aspics or incorporated with other desserts such as a layer of jelly in a cake.

Agar-agar is approximately 80% dietary fiber, so it can serve as an intestinal regulator. Its bulking quality has been behind fad diets in Asia, for example the kanten (the Japanese word for agar-agar [4] ) diet. Once ingested, kanten triples in size and absorbs water. This results in the consumers feeling fuller. This diet has recently received some press coverage in the United States as well. The diet has shown promise in obesity studies. [22]

Asian culinary Edit

One use of agar in Japanese cuisine (Wagashi) is anmitsu, a dessert made of small cubes of agar jelly and served in a bowl with various fruits or other ingredients. It is also the main ingredient in mizu yōkan, another popular Japanese food. In Philippine cuisine, it is used to make the jelly bars in the various gulaman refreshments or desserts such as sago gulaman, buko pandan, agar flan, halo-halo, and the black and red gulaman used in various fruit salads. In Vietnamese cuisine, jellies made of flavored layers of agar agar, called thạch, are a popular dessert, and are often made in ornate molds for special occasions. In Indian cuisine, agar agar is known as "China grass" and is used for making desserts. In Burmese cuisine, a sweet jelly known as kyauk kyaw (Burmese: ကျောက်ကျော, [tɕaʊʔtɕɔ́] ) is made from agar.

Agar jelly is widely used in Taiwanese bubble tea. The bubble teahouses such as Gong Cha and Chatime can be seen in Australia, the United States, the United Kingdom, Middle East and many Asian countries.

Other culinary Edit

In Russia, it is used in addition to or as a replacement for pectin in jams and marmalades, as a substitute to gelatin for its superior gelling properties, and as a strengthening ingredient in souffles and custards. Another use of agar-agar is in ptich'ye moloko (bird's milk), a rich jellified custard (or soft meringue) used as a cake filling or chocolate-glazed as individual sweets. Agar-agar may also be used as the gelling agent in gel clarification, a culinary technique used to clarify stocks, sauces, and other liquids. Mexico has traditional candies made out of Agar gelatin, most of them in colorful, half-circle shapes that resemble a melon or watermelon fruit slice, and commonly covered with sugar. They are known in Spanish as Dulce de Agar (Agar sweets)

Agar-agar is an allowed nonorganic/nonsynthetic additive used as a thickener, gelling agent, texturizer, moisturizer, emulsifier, flavor enhancer, and absorbent in certified organic foods. [23]

Microbiology Edit

An agar plate or Petri dish is used to provide a growth medium using a mix of agar and other nutrients in which microorganisms, including bacteria and fungi, can be cultured and observed under the microscope. Agar is indigestible for many organisms so that microbial growth does not affect the gel used and it remains stable. Agar is typically sold commercially as a powder that can be mixed with water and prepared similarly to gelatin before use as a growth medium. Other ingredients are added to the agar to meet the nutritional needs of the microbes. Many microbe-specific formulations are available because some microbes prefer certain environmental conditions over others. Agar is often dispensed using a sterile media dispenser.

Motility assays Edit

As a gel, an agar or agarose medium is porous and therefore can be used to measure microorganism motility and mobility. The gel's porosity is directly related to the concentration of agarose in the medium, so various levels of effective viscosity (from the cell's "point of view") can be selected, depending on the experimental objectives.

A common identification assay involves culturing a sample of the organism deep within a block of nutrient agar. Cells will attempt to grow within the gel structure. Motile species will be able to migrate, albeit slowly, throughout the gel, and infiltration rates can then be visualized, whereas non-motile species will show growth only along the now-empty path introduced by the invasive initial sample deposition.

Another setup commonly used for measuring chemotaxis and chemokinesis utilizes the under-agarose cell migration assay, whereby a layer of agarose gel is placed between a cell population and a chemoattractant. As a concentration gradient develops from the diffusion of the chemoattractant into the gel, various cell populations requiring different stimulation levels to migrate can then be visualized over time using microphotography as they tunnel upward through the gel against gravity along the gradient.

Plant biology Edit

Research grade agar is used extensively in plant biology as it is optionally supplemented with a nutrient and/or vitamin mixture that allows for seedling germination in Petri dishes under sterile conditions (given that the seeds are sterilized as well). Nutrient and/or vitamin supplementation for Arabidopsis thaliana is standard across most experimental conditions. Murashige & Skoog (MS) nutrient mix and Gamborg's B5 vitamin mix in general are used. A 1.0% agar/0.44% MS+vitamin dH2O solution is suitable for growth media between normal growth temps.

When using agar, within any growth medium, it is important to know that the solidification of the agar is pH-dependent. The optimal range for solidification is between 5.4–5.7. [24] Usually, the application of potassium hydroxide is needed to increase the pH to this range. A general guideline is about 600 µl 0.1M KOH per 250 ml GM. This entire mixture can be sterilized using the liquid cycle of an autoclave.

This medium nicely lends itself to the application of specific concentrations of phytohormones etc. to induce specific growth patterns in that one can easily prepare a solution containing the desired amount of hormone, add it to the known volume of GM, and autoclave to both sterilize and evaporate off any solvent that may have been used to dissolve the often-polar hormones. This hormone/GM solution can be spread across the surface of Petri dishes sown with germinated and/or etiolated seedlings.

Experiments with the moss Physcomitrella patens, however, have shown that choice of the gelling agent – agar or Gelrite – does influence phytohormone sensitivity of the plant cell culture. [25]

Other uses Edit

  • As an impression material in dentistry.
  • As a medium to precisely orient the tissue specimen and secure it by agar pre-embedding (especially useful for small endoscopy biopsy specimens) for histopathology processing [26]
  • To make salt bridges and gel plugs for use in electrochemistry.
  • In formicariums as a transparent substitute for sand and a source of nutrition.
  • As a natural ingredient in forming modeling clay for young children to play with.
  • As an allowed biofertilizer component in organic farming. [27]
  • As a substrate for precipitin reactions in immunology.
  • At different times as a substitute for gelatin in photographic emulsions, arrowroot in preparing silver paper and as a substitute for fish glue in resist etching. [28]

Gelidium agar is used primarily for bacteriological plates. Gracilaria agar is used mainly in food applications.

In 2016, AMAM, a Japanese company, developed a prototype for Agar-based commercial packaging system called Agar Plasticity, intended as a replacement for oil-based plastic packaging. [29] [30]

Watch the video: Easy recipe of potato dextrose agar PDA media to grow fungi