Chilli Flower Drop Off

Chilli Flower Drop Off and Chilli Plant VPD

There are a number of factors that govern whether a Chilli Flower stays on the Branch

The Quick and Most Usual reason is growing indoors produces too low humidity that causes the plant to stay in Vegetative state, try allowing fresh air so the plants feels more like outside if growing indoors

The full explanation always starts with; We all get annoyed at Chilli Plants dropping their flowers and there are causes for this that we can try to control

Firstly, though a little contradiction - Chilli Plants produce lots of pods, that have lots of seeds to grow lots of plants that will grow lots of flowers - in essence chilli plants play a number game and the more they produce the greater the chance of survival and as such they will always produce a little more flowers than they use - so where as a few flower drop offs are natural, a lot falling off is something to do with the following

Factors Governing Flower Drop Off

Infertile Flowers
Humidity - VPD

Chilli Plants have grown in different places round the world, and some have been cultivated to the extent that they are very versatile plants such as the Jalapeno which will grow in almost any environment on the planet except freezing cold, but the Gentlemen in Finland are working on that problem!

However, the majority of them are still classed as wild seeds as opposed to domesticated - this transition can take many many generations before it happens and with the increase of supply of different types the importance of understanding the difference is becoming more important


This is more of a general rule for most Tropical Based Plants that the temperature variation between the coldest part of the day and the hottest shouldn’t exceed 10c

The Plants have evolved by relying on a stable temperature variation

This is particular important to note in Greenhouses and Windowsills where the Glass can trap and store heat releasing again at night creating a big swing in variation

All of this causes the plants genes to be switched on and off confusing its growing cycle and so causes the flowers to have nutrients interruption and alas they die and drop off


There are some that say over feeding the plant can cause flower drop off, I am not a big fan of this idea as the plant as with all plants have a defence mechanism for getting rid of too much nutrients - namely depositing the excess in the leaf and then dropping the leaf

Obviously we are not talking about excessive feeding either where white salty deposits occur on the top of the soil

I do believe that providing the plant with right nutrients at the right time - just as it is important to provide the plant Nitrogen for Green growth, it does require Potassium

Potassium doesn’t make more flowers what it does do is control the cell formation of the plant and makes up  more than 50 plant enzymes

Firstly, a healthier plant cell structure promotes better use of water air and nutrients - the cells travelling have a better balance of these rather than an imbalance

Imbalanced plant cells will then fail to deliver nutrients to the flowers when they require and cause flower drop off

Secondly, enzymes are used by plants to control what is growing and what is not, they control the whole system in affect and what happens and when

When there is a shortage of a nutrient to be able to make these enzymes then obviously they cannot control their respective responsibility creating an imbalance and possible flower drop off

Potassium provides the plant to produce healthy cell structure and enzymes, so ensuring the plant can be balanced in growth and reduce flower drop off

Infertile Flowers (Pollen)

I have placed this section in-between the nutrients and Humidity because both of these play a major part in the fertility stage

As discussed above it is the balanced plant that provides all parts of the plant with nutrients when it needs them in a continuous conveyor belt ensuing a constant cycle of growth

When this is imbalanced due to a lack of nutrients or humidity the plant will not produce pollen and therefore the flower is dead before it started and will eventually drop off

So it is important to appreciate the relationship the plant has with its environment to create a balanced system and hence healthy flowers


This subject is incredibly difficult to explain and understand, and as such I am only going to discuss the effects it has on the plants

Dry Air has low humidity and wet air has high humidity - ideally the relative humidity around the plant should be 60 - 70% which would make it wet air

In basic form, when the air is too dry and the relative humidity is low at 50% or lower the plants start to breathe out too much to compensate for lack of water in the air, this makes the plant concentrate on breathing more creating an imbalanced system that disrupts the growing cycle and hence flower drop off

High humidity - more than 80% will not be a problem in the UK as a general rule as we dont have that type of weather pattern

The relationship between the humidity around the plant and the  plant itself is called VPD or Vapour Pressure Deficit


VPD can be defined as the difference (or deficit) between the pressure exerted by water vapour that could be held in saturated air (100% RH) and the pressure exerted by the water vapour that is actually held in the air being measured.

The VPD is currently regarded of how plants really ‘feel’ and react to the humidity in the growing environment.

From a plant’s perspective the VPD is the difference between the vapour pressure inside the leaf compared to the vapour pressure of the air. If we look at it with an RH hat on; the water in the leaf and the water and air mixture leaving the stomata is (more often than not) completely saturated -100% RH.

If the air outside the leaf is less than 100% RH there is potential for water vapour to enter the air because gasses and liquids like to move from areas of high concentration (in this example the leaf) into areas of lower concentration (the air).

So, in terms of growing plants, the VPD can be thought of as the shortage of vapour pressure in the air compared to within the leaf itself.

Another way of thinking about VPD is the atmospheric demand for water or the ‘drying power’ of the air. VPD is usually measured in pressure units, most commonly millibars or kilopascals, and is essentially a combination of temperature and relative humidity in a single value.

VPD values run in the opposite way to RH vales, so when RH is high VPD is low.

The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant.

As mentioned above, VPD provides a more accurate picture of how plants feel their environment in relation to temperature and humidity which gives us growers a better platform for environmental control.

The only problem with VPD is it’s difficult to determine accurately because you need to know the leaf temperature.

This is quite a complex issue as leaf temperature can vary from leaf to leaf depending on many factors such as if a leaf is in direct light, partial shade or full shade.

The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy.

For humidity control purposes it’s not necessary to measure the actual leaf VPD to within strict guidelines, what we want is to gain insight into how the current temperature and humidity surrounding the crop is affecting the plants.

A well-positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions


I have experimented with nutrients and found the pods shape and size is affected when over fed, rather than flower drop off

The plant will produce a high yield of flower heads based on genetic and the amount of light available

The fertility rate of each flower and whether it turns into a pod or not is in my opinion highly dependent on Humidity and nutrients

A good soil choice and chilli focus will be good for most chilli plants as a standard guide, adding other nutrients and soil types is then just adding to the availability and without over feeding will boost pod production

HOWEVER - Humidity I know will affect the production of fertile flowers and a lack of pollen to produce the pods

So when growing indoors where the environment is man made and less natural the above imbalances will cause flower drop off

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