" Red light and the effect on plant growth | Herbal House NZ

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What is red light and what is its effect on plant growth?

You might already know a little about the light spectrum and how it affects plants, but today we’re going to dive into red wavelengths specifically.

Plants are very sensitive to the red-light spectrum (600-700nm). If you grow with lots of red light, you’ll find that your plants are pretty tall with lots of branches. When growing outdoors, plants will be used to receiving a lot of red light in the summertime. Red spectrum grow lights can help your plants to produce a hormone called meta-topolin which prevents chlorophyll being broken down. This means your plants will stay green and healthy in the Spring and Summer as without chlorophyll, your plants will struggle to convert the light into the sugars it needs to thrive.

What does red light do to plants? 

There are several ways red light impacts your plants. One of the major bonuses is that it can send a message to your plants when it’s the right time to start flowering. If you’re looking to manipulate your plants into having a longer flowering period, you can use red spectrum LED grow lights during the periods of darkness they’d typically get in natural growing environments.

It’s worth remembering however that if you extend the flowering period, you’ll be waiting long before you can harvest your crops.

Red light for plants can also influence the flavor of the crops as it can increase the concentration of certain oils within the plant. Leafy plants exposed to more red light may have a slightly more bitter taste.

Exposing your plants to excessive amounts of red light can reduce the number of ‘female’ seeds your plant produces. This means you’ll be less likely to be able to collect seeds from your plant to continue germinating new plants.
if only red light is used, your plants can become spindly and frail. Sure, they might be tall and have lots of branches, but these branches – and the leaves attached – can be pretty thin and undesirable.

It’s for this reason that we recommend combining red and blue light for plants.

How does far-red light affect plant growth 

Far-red (700-850nm) is at the end of the light spectrum for plants. While previously it was assumed that plants only used red light for growth, research now suggests they can actually respond to wavelengths up to 780nm.

But what does this response entail? 

Far-red light can create a shade avoidance response within your plants. Unlike your sun-loving friend that will have to continuously move their sunbed out of the shade, plants just stretch and extend their leaves and branches into the sunshine.

As well as stretching, far-red can promote flowering and leaf expansion – giving your plants a much larger surface area to absorb the photons they need for photosynthesis.

In our other articles, we’ve discussed the photosynthetic active radiation range, often referred to as PAR. Some research suggests far-red light can even help to enhance the effectiveness of the PAR spectrum.

Blue light vs red light for plants 

Rather than comparing the two light waves, it’s much better to combine the two to create fresh, green and healthy crops. There is such a thing as too much of a good thing, and your plants won’t reach their potential if you don’t use a combination of blue, red and green wavelengths.