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How much light does my plant need?

How much light does my plant need?

From all the elements surrounding your houseplants light seems to be one of the most open to interpretation.

When you hear that your lovely brand new plant requires bright indirect light but no harsh direct sunshine what does it actually mean?

Let’s start from the basics:

Light is absolutely vital for your plants because without it, the chemical process called photosynthesis, is not able to happen. Photosynthesis happens in the green parts of the leaves, where little cells called chloroplasts produce it’s fuel.

Below you can see the very basic formula of the process:

This formula highlights that without sunlight the plant can’t produce glucose and oxygen, the fuel it needs to live.

Different plants require different intensities of light. The best way to understand your plant lighting needs is to figure out what its natural environment is. For instance, most cacti grow in a very intense bright direct sunlight in the desert and can withstand very intense scorching sun. This is because they don’t have thin, delicate leaves, which would burn. Instead they have adapted by producing thick waxy skin and large fleshy stems to reduce the loss of water and reflect the heat. Another species, such as jungle plants, usually grow on the jungle floor and receive bright, filtered light streaming through the taller plants and trees around it. Because of this they often climb the surrounding trees to reach the brighter light higher up in the canopy. Once they reach these higher heights, they will develop larger leaves as they can sustain these with the extra fuel produced from the extra light they receive.

The same applies to your houseplants. Some plants may survive in a lower light conditions, but their leaves will not grow to their full capacity, because they don’t receive enough light to supply the energy needed to sustain larger leaves.

Below I have tried to define some of the different levels of light you may find on most common indoor plant care instructions (bear in mind the further north or south you are from the equator, the less intense the sun rays are):

Bright direct light – south facing window sill or conservatory in your home. Although any light reaching your plants through the window glass is filtered, it is still extremely intensive here at noon, especially on hot, sunny days. There aren’t too many plants that can put up with this. Some examples would be cacti and some succulents that should thrive here. If the leaves of your plants (even the sun loving ones) start to lighten/yellow in patches – try moving them a couple of feet away from the window as this may actually damage your plants.  

Plants placed on the bench in front of a south – west facing window, receiving bright indirect light filtered by the row of plants on the window sill.

Bright indirect light – near by a south facing window with filtered light or alternatively a west facing window*. This is the best light condition for most jungle plants. The light is still very bright but it is usually diffused by some kind of barrier before reaching the plant. In the jungle this will usually be higher canopy plants, in your home – a sheer curtain or a few feet distance from the direct light source.

Medium light – East facing window, as well as north facing windows in summer. These will usually receive morning light and moderate light throughout the day. Perfect place for begonias, orchids or dumb canes. This light is usually best for plants with quite delicate leaves which would otherwise scorch in too bright a light. These plants usually grow on the jungle/forest floor but do not reach too greater hight.

Understanding light intensity in a south – west facing room. Plants in the window receiving bright direct light. Plants on the floor by the window receiving bright indirect light. Opposite side of the room gets medium to low light. Later on in the day some bright indirect light shines through to the opposite side due to the angle the sun comes through the window (in spring/autumn).

Low light – north facing window sill in the winter months or a fair distance from a south facing window. Despite what many websites say there aren’t that many plants that will thrive in low light conditions. Even though some plants such as Peace Lilly, Sansevieria or ZZ plant will SURVIVE in lower light conditions, they will not thrive. As long as they are getting some light they will most certainly not die, but also growth will be very limited or almost non-existent. This can be fine if your plant is already quite large and you purposely want to reduce their growth. If you place bright light loving plants in lower light conditions their growth will not only be reduced, but they may also produce so called leggy growth. This means the stems will grow long with small leaves growing few and far between.

LOW LIGHT DOES NOT MEAN NO LIGHT.

Generally speaking, plants need to be placed near a window or they will require extra light sources to grow (eg. grow lights – another detailed post coming soon).

How much light a plant receives also influences how much and how often you will need to water your plants (which I explain in more detail here).

Lastly, a little tip on how to check which way your window faces – use the compass on your phone.

iPhone 7 compass

This is NOT an exhaustive explanation. I have tried to condense this as much as possible and will try to write more about in the future. You could easily write a whole book about it.

*(in summer at midday, west facing windows may actually receive quite a bit of direct light so please watch your plants and move them away on any signs of over-exposure)

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