Jorge, Plants

Green plants appear green due to a pigment called chlorophyll that primarily absorbs blue and red wavelengths of the visible light spectrum, but reflects a portion of green wavelengths. This green light enters our eyes and hits the light-sensitive retinas, in which there are cone cells, that once stimulated, sends a signal to our brain that interprets the information, giving the colour green. Therefore it can be stated that the colours of an object is dependent on what colours are reflected (or transmitted) back to our eyes. (Technically speaking,  visible wavelengths have no colour. Colour is created in the brain.)

Most humans are trichromats, and possess three types of cone cells sensitive to red, green and blue light, named L M and S respectively. Each cone allows us to distinguish around a hundred shades, so the total number of combinations is at least a million. Colour is determined by our brains that interpret the different ratios of these three colours.

The visible light spectrum ranges from approximately 400nm to about 700nm. Our brain attaches different colours to different wavelengths with blue at about 475nm, green at about 510nm and red at about 650nm. Picture Credit: Vanessaezekowitz (2007) licensed under CC BY-SA 3.0.

Not all humans, or all animals, perceive colour in the same way. Dichromats, such as dogs, possess two types of cone cells and can distinguish blue and yellow, but not red and green. Their vision is similar to some colour blind humans, who only have two working cone cells due to either an absence or a malfunction of a third type of cone cell. Not all colour blind humans are the same as they can have different combinations of working cone cells (or none at all), and thus are unable to see different colours, resulting in different colour spectrums.

Some animals are tetrachromatic and able to distinguish to four primary wavelengths of light. Birds, for example, are even able to view ultraviolet light, which is beyond the visible light spectrum. (Interestingly, humans with Aphakia can also view ultraviolet as their lens has been surgically removed. For the rest of us, our lens blocks this light.)

Some women are tetrachromatic as they possess four types of cone cells, which allows them to see a hundred million colours. The extra cone cell has its origin in their fathers’ colour blindness, who possess two working cone cells and one mutant one. This mutant one is passed on to the daughter, who then has four cone cells. It is probable that tetrachromats have to train themselves to see such an array of colours, as the natural world will not have such a diversity of colours for the brain to learn to use the fourth cone. As such, it is likely that most will go through life without recognising their potential.

The absorption spectrum of a bird’s (Estrildid finches) four cone cells.

So tetrachromats, both human and non-human, can distinguish many more hues of green than  the rest of us, and plantlife may appear very different. For animals like birds this may be very useful for distinguishing between plants to find sources of food or shelter.  For the rest of us, our trichromatic vision proves very useful in allowing us to quickly identify between opportunities for profit and sources of danger, such as when fruits are ripe.

Plants need to absorb light in order to carry out photosynthesis to produce glucose, which can be used for metabolism and growth, or stored as starch. Photosynthesis is a chemical reaction that inputs sunlight, water and carbon dioxide and outputs glucose and oxygen. It is a two step process, comprised of light-dependent and light independent reactions. In the former sunlight plays a key role by providing the chlorophyll with energy to kickstart the complicated chemical reaction.

In green plants, there are two types of chlorophyll: chlorophyll a and chlorophyll b that both absorb different spectrums of light. They both complement each other with a absorbing more red light and b absorbing more blue, and this allows the plants to fulfil its energy requirements. As you can see in the graph below, chlorophyll still absorbs green light but not to the same extent as they do red and blue.

Picture Credit: Daniele Pugliesi (2008) modified by M0tty licensed under CC BY-SA 3.0.

However, this is not the full story. The above graph represents the absorption spectra of extracted chlorophyll molecules. As part of a plant, chlorophyll never exist alone but are bound to molecules that influence what it absorbs, and as such plants absorb about 70% of green light.

There are other pigments (accessory pigments) inside green plants that play a role in photosynthesis such as carotenoids. They primarily absorb green and blue, but reflect yellow, orange and red. It is these pigments that give many plants’ leaves their autumnal colours, and signal the presence of ripe fruit, once the amount chlorophyll is reduced. These accessory pigments are useful as they allow the plant to capture more of the sun’s energy by broadening its absorption spectrum.

So, what about plants that aren’t green? While all plants that photosynthesise contain chlorophyll a, they can contain many different types of accessory pigments, giving them different colours. For example, many reddish-purple plants contain the pigment anthocyanin in such abundance that acts to mask the green chlorophyll pigments.

So, why do plants use red and blue light more so than green? And why do they not absorb all visible light (and henceforth appear black)?

It is believed that today’s plants evolved from a common ancestor (green algae) that used chlorophyll to photosynthesise. Why no alternative dominant pigment emerged is an unanswered question, although many hypotheses have been proposed. Evolution is a product of multiple processes such as random mutation, random selection and natural selection, and henceforth plants can’t design or choose the best pigment to use. It is therefore probable that once chlorophyll proved successful no new alternative dominant pigment emerged, thus enabling green plants to dominate the landscape. Although, there is a possibility that (primarily) utilising a narrow band of wavelengths (red and blue) for photosynthesis is mechanically superior, and this allowed early organisms to outcompete other lifeforms.

For more discussion on why plants use chlorophyll, and are henceforth green, can be found here, here and here.

Why do plants use the visible light spectrum for photosynthesis?

In general, plants only absorb trivial amounts of light outside of the the visible light spectrum. This is because the sun produces the most light in the visible light spectrum, and chlorophyll have evolved to utilise it. (If you look at the graph above, chlorophyll a’s absorption spectrum is almost exclusively confined within the visible light spectrum.) There are other mechanical reasons for this. Visible light is perfect as it provides just enough energy without causing damage to the plants’ cells. By contrast, ultraviolet is damaging and infrared contains insufficient energy. In addition, a lot of ultraviolet light is blocked by the ozone layer.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

Flowers, Gardening, George, How To, Infographics, Planting, Plants

No plants will survive very long without good watering, and it’s even more crucial for potted plants. They may not have the same access to rainwater, drainage or natural water reserves depending on where they are placed. So here is our handy infographic to remind you how to water pot plants for great growing!

If you’re looking to give your potted plants a fabulous new home, then you’re in luck. At Primrose we have an incredible selection of all kinds of planters available.

How to water pot plants

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Catch up on the previous post in the series: How to Repot a Plant.

Next up is Part 4: How to Choose the Right Planter for Your Garden.

George at PrimroseGeorge works in the Primrose marketing team. As a lover of all things filmic, he also gets involved with our TV ads and web videos.

George’s idea of the perfect time in the garden is a long afternoon sitting in the shade with a good book. A cool breeze, peace and quiet… But of course, he’s usually disturbed by his energetic wire fox terrier, Poppy!

He writes about his misadventures in repotting plants and new discoveries about cat repellers.

See all of George’s posts.

Gardening, George, Grow Your Own, Hedging, How To, Plants

Caring for topiary

Growing topiary is one of the most magical arts you can master as a gardener. We all love the huge hedge animals and blooming box clouds. But maintaining and caring for topiary plants can be a lot of effort, so we’ve broken down the steps into our top tips. Keep this checklist handy as you get to work on your creations!

  1. Plant your high hedges wide as they’ll need a lot of root space.
  2. Topiary needs aerated soil so make sure it doesn’t become waterlogged. Use good compost, bark mulch and grit.
  3. Feed your plants with slow release fertiliser granules, and Growmore once every spring.
  4. Water regularly over summer and give a light watering in winter.
  5. Sterilise your cutting equipment with antibacterial spray to avoid transfer of disease.

Clipping topiary hedges

  1. Clips your plants into shape once or twice a year. During summer is the best time to do this – start after frost season is definitely over and finish up by September.
  2. Only cut the topiary on an overcast day as bright sunlight will scorch the leaves.
  3. Experts recommend trimming first with power tools for speed, then cleaning up with sharp shears.
  4. If you’re training growing branches then use soft twine so it doesn’t cut into the wood.
  5. Watch out for signs of disease. Box hedges are particularly affected with box blight and box suckers. Yew can be hit with phytophthora root rot.
  6. If your topiary has been neglected then hard prune it in early spring to get it back into shape. Then give it plenty of feed and mulch.

Topiary maintenance

We hope these tips will get you started on the path to topiary perfection. If you have any other points on how to care for topiary then please share in the comments below!

George at PrimroseGeorge works in the Primrose marketing team. As a lover of all things filmic, he also gets involved with our TV ads and web videos.

George’s idea of the perfect time in the garden is a long afternoon sitting in the shade with a good book. A cool breeze, peace and quiet… But of course, he’s usually disturbed by his energetic wire fox terrier, Poppy!

He writes about his misadventures in repotting plants and new discoveries about cat repellers.

See all of George’s posts.

Composting, Gardening, Jorge, Plants

mycorrhizal fungi
A mycorrhizal fungus as viewed under the microscope. Picture credit: Dr. David Midgley (2007) licensed under CC BY-SA 2.5.

Mycorrhizal fungi rootgrow has become a common feature of garden centres of late, and has been advertised as a product that can greatly boost your plant’s health. But does it really work? And when should I apply it?  Before delving into such questions, it would be worthwhile to explain what are mycorrhizas.

What are Mycorrhizae?

The etymology of Mycorrhiza comes from the Greek mykos “fungus” and riza “root”. And this is precisely what mycorrhizae is, a symbiotic relationship between fungi and plants. It occurs in nearly all plant life on land and is thus suspected of being one of the key factors that allowed plants to colonise the land.

The relationship is symbiotic as the fungi and plant provide one another with nutrients that each are maladapted to garner independently. It has its origin in the fact each are different types of organisms, with fungi being heterotrophic and plants autotrophic. Heterotrophs, such as humans, absorb their nutrients from organic sources, but can’t produce energy from inorganic sources. Autotrophs, on the other hand, can produce energy from inorganic sources such as sunlight. Plants do this through the process of photosynthesis that produces carbohydrates. As autotrophs, plants also find it difficult to absorb essential nutrients such as nitrogen and phosphorus.

Mycorrhizal fungi located inside a flax root’s cortical cells as viewed under the microscope.

And this is where the fungi come in. The fungi that can easily absorb such nutrients interacts with the plant’s root system, which the plant willingly allows, providing such nutrients in return for the carbohydrates that itself cannot produce.  It does this through expanding its roots’ surface area that can absorb nutrients and water. They also provide the additional benefit of increasing a plant’s resistance to pathogens, preventing root disease.

As a side-note, the mycorrhizas were once divided into broad groupings, the ecto (outside) and endo (inside) varieties, with the former (usually) coating the root cells and the latter intermeshing into the plant root cells; although today they have been divided into new sub-categories or superseded with new typings. The endo varieties are difficult to spot, while the ecto varieties presence may be hinted at with the appearance of toadstools, or coated, oddly-branched roots.

The Leccinum aurantiacum – an ecto variety of mycorrhizal fungus. Picture Credit: Tomas Čekanavičius (2006)  licensed under CC BY-SA 2.5.

Do I Need to use Mycorrhizal Rootgrow?

It is suspected that neither fungi nor plants could survive in many situations without such a relationship. Mycorrhizas is fairly ubiquitous throughout the soil, and can infect a wide range of plants, so it is highly probable that suitable plants will become infected in their lifetime. There may be some exceptions to this, such as heavily cultivated soil and isolated rocky outcrops, but more on this later.

Scientifically, there is little evidence supporting the use of mycorrhiza rootgrow. The British Standards Institution, which produce technical standards on an array of products, does not recommend using the rootgrow for planting trees as a matter of routine. At Texas A & M University, a team grew plants in soils with and without mycorrhizas and found that the infected plants grew slightly better at the planting-out stage, although any advantage disappeared completely after two seasons in the ground. This was because all the plants ended up infected with mycorrhizas anyway. Finally, a test by Which? Magazine found that the potting compost brand that contained mycorrhizas performed poorly, although such an outcome may be down to other factors.

So are mycorrhizas products any good at all? In all probability mycorrhizas products will be unlikely to confer any long term benefits to your plants, unless you have good reason to suspect that your soil is deficient in mycorrhizas. (It is important to check that your plant can benefit from mycorrhizas in the first place.)

Heavy use of phosphorus in agriculture reduces the incidence of mycorrhiza in the soil. The element is also used to ignite matches.

As already stated, heavily cultivated ground may reduce the occurrence of mycorrhizas. This is because fungicide is naturally destructive to fungi, although, interestingly, it is phosphorus-rich soil that is especially detrimental to mycorrhizas. Mycorrhizas usually function to gather this rare resource for plants, but an abundance of it, usually created by fertiliser, actually suppresses it. Why this is the case is unclear, although it can be in a sense expected, as messing with the ecosystem can have untold effects. Sadly, in this case using mycorrhizas rootgrow is unlikely to have any effect, as if the soil is not conducive to mycorrhizas, the best option will be to stop using phosphorus rich fertilizers, and wait for the mycorrhizas to return naturally.

There may be reason to use mycorrhizas in some cases, perhaps for isolated plants, and plants that are indoors (although such cases are unlikely to be common).

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.