Yuzu (Citrus junos)

Yuzu tree

What is yuzu?

Yuzu (Citrus junos Sieb. ex Tanaka) is a citrus that is believed to have originated from the Hubei Province, along the Yangtze River in China. It is believed to be a natural hybrid of the Ichang papeda (Citrus cavaleriei), a small wild species of lemon, and the mandarin (Citrus reticulata). This fruit was introduced to Japan over 1,000 years ago during the Tang dynasty.

Yuzu is an essential ingredient in Japanese cuisine, particularly in the Kōchi Prefecture, where it is widely cultivated. The fruit’s unique aroma and tart flavour make it a versatile ingredient that is used in everything from marinades and dressings to desserts and beverages. Yuzu is also used in traditional Japanese medicine for its health benefits, which include reducing inflammation and relieving symptoms of colds and flu.

In recent years, yuzu has gained popularity around the world for its distinct flavour and fragrance. It has become a sought-after ingredient in high-end restaurants and cocktail bars. As a result, yuzu has become an important part of global culinary culture and is now cultivated in various regions outside of Japan.

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The Secret Life of Flowers: Why Do They Close at Night?

Why do some flowers close at night?

Why do some flowers close at night?

This is an evolutionary process known as nyctinasty, which originated from the Greek word Νύχτα, which means night. Nyctinasty refers to a type of movement (nyctin) that serves a number of functions.

  • To protect the delicate pollen and reproductive parts from moisture at night as is important that pollen remain dry so that it is easily transferred onto visiting insects as they feed during the day.
  • As most pollinating insects are active during the day, there is no benefit to keeping the flowers open.
  • The petals and in some cases bracts fold over and act as a protective blanket against the nighttime cold and against herbivorous insects.

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Christmas Plants and Their Toxicity to Dogs

Christmas plants toxic and non-toxic to dogs

Christmas plants and pets

During the Christmas period, many homes are decorated with plants. Knowing which ones are safe and which ones are potentially dangerous can save pet owners an emergency trip to the veterinarian. This list includes some of the most common Christmas plants and includes the toxic properties.

Although many of the plants are labelled non-toxic, ingestion of large amounts of any plant matter can cause gastrointestinal upset.

Related: Caring for a Christmas tree

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Is Seasol Toxic to Animals?

Is Seasol toxic to animals?

Seasol is not toxic to animals and is safe to use on plants in homes with pets as long as care is taken.

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Lenticels (Bumps) on Dahlia Tubers

What are lenticels?

What are lenticels?  Ι     How is gas exchanged via the lenticels?   Ι   Lenticels on dahlia tubers   Ι   What is the difference between lenticels and gall?

What are lenticels?

Lenticels are raised breathing pores or protrusions located in the periderm (the thickened protective outer layer) and skin of certain plants and fruit. Their function is to allow the exchange of oxygen and carbon dioxide to and from the internal tissues.

The protective layer of the dahlia tuber, similar to the periderm in woody plants, is made of compacted cells that are largely impermeable to gases. Lenticels interrupt this layer, allowing for necessary gas exchange. This exchange of gases is critical for the living tissue located beneath the periderm.  Cells within the lenticels contain small spaces known as ‘intercellular spaces‘, which provide a pathway for gasses to move between the internal tissues and the outside environment.

The term ‘lenticel‘ comes from the Latin word ‘lenticula,’ which means ‘small lentil’, about the raised, lens-shaped spots on the surface of a plant stem, tuber or fruit that resemble the shape of a lentil.

What’s the difference between stomata and lenticels?

While lenticels and stomata perform similar functions, they are not the same.

Stomata (singular: stoma) are tiny pores found on the surface of leaves and young green stems. These pores are surrounded by two specialised cells known as guard cells. Guard cells control the opening and closing of the stomata. The primary function of stomata is to regulate the exchange of gases, particularly water vapour and carbon dioxide, between the plant and the environment. When stomata are open, carbon dioxide can enter the plant for use in photosynthesis, while water vapour is released into the air as a byproduct of transpiration. When stomata are closed, the plant conserves water and reduces the loss of water vapour.

LocationFound primarily on leaf surfaces (especially lower surfaces). Can also appear on young green stems.Located woody stems, fruits, and other woody parts of the plant.
StructureMade up of two guard cells surrounding a pore.Spongy areas in the periderm with loosely arranged cells, lacking
specialised cells like guard cells.
Primary FunctionFacilitate uptake of CO₂ for photosynthesis and release O₂.Facilitate gas exchange (O₂ in, CO₂ out) in woody tissues.
RegulationRegulated by guard cells based on various internal and external
No active regulation; spongy tissue remains open to the atmosphere.
DevelopmentDevelop from specialised epidermal cells.Result from the activity of the cork cambium and subsequent periderm
AppearanceTypically microscopic, requiring a microscope for clear observation.Often visible to the naked eye as small, raised, rough spots or
lines on woody surfaces.
Additional FunctionsPlay a significant role in transpiration (water vapour loss).Allow underlying tissues to respire by providing O₂ and releasing
CO₂, especially where other forms of gas exchange are restricted.


How is gas exchanged via the lenticels?

The process of gas exchange occurs through diffusion, which is the movement of molecules from an area of high concentration to an area of low concentration. Oxygen and carbon dioxide molecules move from areas of high concentration outside the plant to areas of lower concentration inside the plant, or vice versa, through the pores of the lenticels.

The rate of gas exchange through lenticels depends on several factors, such as the size and number of lenticels, thickness and permeability of the epidermis, temperature and humidity of the surrounding environment, and the metabolic activity of the plant.

In addition to facilitating gas exchange, lenticels also play a role in regulating the water balance of the plant. They can become more or less permeable to gases and water depending on the environmental conditions, helping to prevent the plant from losing too much water through transpiration.

Lenticels on dahlia tubers

When dahlias are exposed to prolonged wet conditions, the tissues in the lenticels swell and become more pronounced in a condition called ‘lenticel hypertrophy‘.  Air-filled spaces known as soil pores decline in waterlogged soil, which starves the roots and tubers of oxygen. When a plant experiences excess moisture, lenticels become more permeable, which allows for a greater exchange of gases and water vapour. This increased permeability can cause the lenticels to swell, becoming more prominent on the surface of the stem.

When dahlias endure extended periods of dampness, a phenomenon known as lenticel hypertrophy occurs, wherein the lenticels undergo enlargement and become more conspicuous – a condition often first noticed by gardeners during such wet spells. The presence of excess water causes a reduction in the air-filled cavities within the soil, termed soil pores, leading to an oxygen deficit for the roots and tubers. In response to the heightened moisture levels, the lenticels enhance their permeability to facilitate a more robust exchange of gases and water vapor. This adaptive response, lenticel hypertrophy, results in the noticeable swelling of these structures on the dahlia’s stem surface.

Anaerobic (which means ‘without air‘) respiration is a type of respiration that occurs when plants have limited access to oxygen. During anaerobic respiration, plants produce ethanol, which can build up to toxic levels in the plant tissues. Lenticels provide a more efficient and safer exchange of gases including oxygen which is necessary for aerobic respiration.

Injury to the stem can also cause lenticels to swell. When a plant is wounded, the cells in the surrounding tissue can release chemicals that stimulate the production of new cells and the formation of calluses. As this process occurs, the lenticels near the injured area may become swollen, as the increased activity of surrounding cells causes the pores to enlarge.

Lenticels in dahlias are cosmetic only and do not impact the health or growth of the plant.

Lenticels and dahlia storage

While lenticels serve an important function, they can impact the storage life of dahlia tubers. During storage, dahlia tubers respire, consuming oxygen and producing carbon dioxide and water vapour. If dahlia tubers are stored in an environment with high humidity, the lenticels can become more permeable, allowing for greater gas exchange and leading to increased water loss and faster deterioration of the tuber.

Additionally, the presence of lenticels can provide a site for infection by fungi or bacteria, which can further reduce the storage life of the tuber. In some cases, the lenticels may even serve as an entry point for insects or other pests, which can damage or feed on the tuber and further reduce its quality.

Dahlia tubers with fewer lenticels may be more resistant to moisture loss, and fungal and bacterial infections, leading to a longer storage life. Other factors such as temperature, humidity, and the presence of pathogens can also play a significant role in the storage life of dahlia tubers. Proper storage conditions, including cool temperatures and low humidity, will extend the storage life of dahlia tubers, regardless of the number of lenticels present.

What is the difference between lenticels and gall?

Crown gall, or gall, is a serious bacterial infection caused by the soil-borne bacterium Rhizobium radiobacter (syn. Agrobacterium tumefaciens) which occurs on woody shrubs and herbaceous plants. Affected dahlias develop distorted growths on the crown (base of the stem) of the tuber. Dahlias with crown gall should be carefully disposed of in the garbage, and not composted.

Take care when handling dahlia tubers to avoid damaging them, which provides an entry site for the R. radiobacter. Solarisation can help to reduce the number of pathogens in the soil.


  • Lenticels are small, corky structures that facilitate gas exchange on the surface of dahlias and other woody plants.
  • Normally, lenticels are difficult to see with the naked eye, however, when exposed to prolonged wet conditions, lenticels swell and become more visible.
  • Regular inspection of stored dahlia tubers can help prevent the spread of disease and ensure a healthy growing season.

Is Gardenia Toxic to Dogs?

Is gardenia toxic to dogs?

Gardenia is toxic to dogs. The toxic principles are crocetin, geniposide, genipin, geniposide and saponins which cause mild gastrointestinal upset, and in some cases, cardiac and nervous system disorders.

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Understanding Transplant Shock: How to Save Your Plants

What is transplant shock in plants?

What is transplant shock?  Ι  When is transplanting necessary?   Ι   How long does transplant shock last?   Ι   What causes transplant shock?   Ι   How to safely transplant a plant Ι   Desperate times call for desperate measures

What is transplant shock?

Transplant shock occurs when a plant is moved or transplanted from one location. This may include repotting a plant, moving a plant from the ground to another location, or transferring seedlings. Common signs of transplant shock include decreased growth, leaf scorch (yellowing/browning of the leaves), curling leaves, leaf, flower or fruit drop, wilting, and eventually, the plant may die.

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Is Hyacinth Toxic to Dogs?

Is hyacinth toxic to dogs?

Hyacinth is toxic to dogs, the toxic properties are insoluble calcium oxalate crystals that penetrate the delicate oral tissues causing intense pain and burning.

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The Benefits of Pinching Your Dahlia Plants

When to pinch dahlias

Why pinch out dahlias?

Also known as stopping, pinching out is a technique used by gardeners to remove the tip (apical bud) of a plant to promote the growth of lateral (side) branches, resulting in a fuller plant and more flowers. The apical or terminal bud is the bud located at the tip of the plant where elongation and new growth occur. It was initially believed that auxins,  a class of plant hormones produced in the apical bud, exerted an inhibitory effect on axillary (side) bud growth. However, recent evidence indicates that apical dominance strongly correlates with the availability of sugar. Essentially, the shoot tip’s demand for sugar is so high that axillary buds do not receive adequate sugar for growth.

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Beating Pythium Infection: A Guide for Gardeners

Pythium infection in plants

What is Pythium?  Ι   Life cycle  Ι   Dispersal  Ι   Signs of root rot in plants  Ι   How to treat root rot  Ι   Sterilising equipment   Ι  How to prevent a Pythium infection

What is Pythium?

Pythium (pronounced pie-thee-um), are parasitic oomycetes (water moulds) made up of 200 species worldwide¹, most of which are pathogenic to plants. Oomycetes along with fungi are the most common pathogens involved in root rot and damping off, both of which are highly fatal to their host.

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