How to Prevent Fruit Rot in Hydroponic Systems

How to prevent fruit rot in hydroponic systems is something growers need to prepare for and know how to manage when it happens. More importantly, it helps to understand what causes it and how to prevent it from happening in the first place; prevention is always better than cure.

Successful hydroponics is the healthy nourishment of plants based on a balance of things all working harmoniously together. But sometimes, this can become imbalanced, and rot can develop in our plants. 

What are the Fruit Rot Symptoms in Hydroponic Systems?

Fruit rot in hydroponic systems is also known as Blossom-End-Rot or BER. There is no mistaking that there is something wrong with the plant when it sets in.

In otherwise healthy plants, fruit rot generally starts around the time the fruit of the plants is around the halfway-grown stage. The appearance is of water-soaked abrasions or bruising, which are a very light brown and which, when untreated, become more significant and much darker, with a leathery texture. There may be a couple of these areas on the fruit, or the blight may cover half of it. The spots then dry out completely and develop a more flimsy appearance, paper-like and a lighter colour.

Once this has established itself, the plant will become vulnerable to other diseases and blights, and if not treated, this could cause all sorts of unsightly infestations, starting at the fruit.

What Are the Causes of Fruit Rot?

Fruit rot happens when the fruit grows faster than the amount of available calcium. Some plants are more susceptible due to the genetics of the plant itself, although climate does play a part. 

Calcium is one of the macronutrients supplied to plants within the nutrient solution. Low pH levels are another cause of this disease. Yet another cause is too dry or too wet conditions.

All the elements used in the hydroponic process (both macronutrients and micronutrients) need transporting to all parts of the plant that need them, and they each have their role to play in the plant’s growth and successful development. 

Some elements are easier to deliver throughout the plant than others. Calcium is not particularly good at finding its way quickly to where it’s needed. Its delivery to the plant is somewhat sluggish, so if the water, or the nutrient solution, is interrupted for whatever reason, then this is where calcium delivery can be stopped or drastically curtailed, and this is when fruit rot can set in.

Because plants can outgrow the supply of calcium, it isn’t surprising that those plants which grow more quickly than others are more susceptible to the disease.  

On a chemical level, other things which can influence this include a high salt (EC) concentration or ammonium used in the nitrogen within the nutrient solution (nitrogen being an essential nourishing macronutrient in the hydroponic process). 

The Cause of Fruit Rot in Hydroponic Systems

The blemish known as ‘tip burn’ is another result of the shortage of calcium in the uptake supply of plants in hydroponics and is very much associated with fruit rot.

Because of this lack of calcium, it can take a while to discover fruit rot or tip burn. We can check and double-check and find that there is undoubtedly a good supply of calcium within our nutrient solution or even more than normal levels of calcium. 

While tip burn occurs in lettuce, strawberries, greens and herbs, fruit rot will affect tomatoes and peppers (capsicum) more than other vegetables. 

A constant supply of calcium helps the growing parts of plants, as, once established in other regions, the calcium stays there and never leaves that part of the plant. Therefore a continual supply of calcium is always needed for as long as the plant grows. The older leaves retain a healthy amount of calcium in plants with fruit rot, and the younger leaves consistently demonstrate the disease.

Both tip burn and fruit rot result from this calcium transport and delivery failure. Xylem and phloem are two types of tissue within a plant responsible for the healthy transportation of nutrients. Xylem tissues transport water and dissolved nutrients to the leafier parts of the plant. Xylem and phloem transport the minerals and sugars around the plant where they’re needed.

Transpiration is the natural, continual process of losing water from the leaves to the air, creating an absence of water which stimulates the xylem tissues’ delivery system to replenish it. As calcium travels via the xylem tissues, anything which can cause water loss will also cause a loss of calcium nourishment for the plant. The same goes for anything which endangers the xylem tissue itself.

Calcium moves sluggishly or not at all. When transpiration occurs, calcium escapes into the atmosphere with water. Therefore to ensure a reasonable rate of calcium delivery, you need to have a rate of transpiration which is uniform and constant, with no sudden spikes or peaks in its speed. Because when this rate suddenly increases, the supply of water (and calcium) from the xylem cannot keep up with it, increasing the danger that tip burn or fruit rot can set in.

The transpiration rate can be kept steady by keeping the humidity below 90%. You should also note that the effect of a gentle breeze on the surface of the leaves, as caused by oscillating fans, will also help this process, summoning the water-borne calcium brought by the ever-industrious xylem tissues.

There is a direct correlation between low amounts of the micronutrient boron and low calcium uptake in the plant; therefore, you should check for the concentration of boron within the nutrient solution in the plant’s root system.

So as you can see from all the above, it isn’t just the level of calcium in your nutrient solution which determines how susceptible a plant is to fruit rot and tip burn. Other factors also allow (or restrict) calcium uptake within the plant, controlling how likely your plants will succumb to these diseases.

How to Prevent Fruit Rot in Plants in Hydroponic Systems

You can prevent fruit rot in plants in hydroponic systems or minimise it by taking several courses of action. 

Fruit rot likes conditions of high humidity. The disease particularly likes it when high humidity and high temperature prevail together, so it’s best to take preventive measures against both. 

Check EC levels in your hydroponic system; high levels of EC within the nutrient solution can lead to a lower uptake of calcium if your nutrient solution is too salty. A quality conductivity meter like the Bluelab Truncheon will prove invaluable.

You can reduce fruit rot using a Calmag supplement mixed into your nutrient solution or as a foliar spray applied directly to your plants. You should make a point of spraying the green fruits of the plant because if you spray just the leaves, it will not affect the spread.

Apart from other factors inhibiting calcium uptake within the plant, there is always the possibility of too little calcium within the system, merely an inadequate amount of it in the nutrient solution. But – and this is almost universally true – because the nutrient solution we use is produced commercially to exacting standards, the chances of this happening are next to impossible.

Problems with calcium uptake in plants may be due also to a high incidence of sodium, potassium, ammonium or magnesium in the nutrient solution. And the high salinity already mentioned may be due to low temperature in the plant’s roots and high humidity, leading to the sluggish movement of fluids in the plant.

Reducing the salinity (as measured by EC levels) in your nutrient solution will lead to increased water uptake, and more calcium can transport to the plant areas that need it most. These are the newest developing parts and potentially the fastest growing, whose growth rate is always in danger of outstripping the supply of calcium via the uptake process.

One beneficial tactic is to lower the EC levels during the night. Calcium is concentrated and transported into the growing leaves much more at night than during the day, so reducing the EC levels at night can help the uptake process.

There are plants which have been specially ‘bred’ so that they have a genetic predisposition to flourish without succumbing to either fruit rot or tip burn. These specially bred strains are known as cultivars. So a straightforward expedient is only to grow those cultivars which have been bred specifically for this purpose. 

You should also note that the well-balanced nutrient solution that you bought may, through time, have turned into something far less balanced if the excess solution is allowed to drain back into the reservoir. Over time some impurities may get into the mix as well. So after a while, you’ll find that it isn’t the well-balanced solution you originally bought. That’s why it’s always advisable to keep testing it regularly. 

Environmental factors play their part. Watch out closely for those conditions which tend to foster calcium disorders, such as incorrect temperature and high humidity. 

Water stress happens when the supply to plant roots reduces or transpiration levels increase drastically. It seems as if it occurs suddenly but in reality, it has been building up for a while owing, if truth be told, to the grower’s negligence.

As mentioned above, the provision and careful placing of fans that provide a gentle breeze across the leaves to aid transpiration is another suitable measure to prevent fruit rot and tip burn.

Follow this sound advice, and you will probably never need to ask how to prevent fruit rot in hydroponic systems or be bothered by these perplexing and unsightly diseases which may ruin your entire crop.