When your plants start to show signs of poor health, such as yellowing or withered leaves or stunted growth, it may be tempting to try and diagnose a nutrient deficiency as quickly as possible so that you can start treatment right away.
Going on visual appearances alone, this will quickly become complicated, as many common nutrient deficiencies in plants share the same or strikingly similar symptoms. In addition, your plants are more likely to be suffering from a combination of nutrient deficiencies or toxicities at the same time as opposed to a single one, which makes it even tougher to diagnose this accurately.
That said, there are a number of potential causes when it comes to signs of poor plant health, such as incorrect pH, water quality issues, pests and more. In this post, we'll go into more detail on each of these potential causes, which you should look into before attempting to diagnose or treat a standalone nutrient deficiency.
Before we get into our list of all the things you should check before starting any nutrient deficiency treatment, it's important that we briefly look at what a nutrient deficiency is and how it may come about.
For plants to achieve optimal health, they need to have access to a balanced range of nutrients. Whether you're growing your plants in soil or hydroponically, you need to make sure that not only are they able to get the right amount of nutrients, but they also need to be getting the right balance of nutrients.
When it comes to this balance of nutrients, your plants will need larger amounts of a set of nutrients known as the macronutrients. These macronutrients include nitrogen, potassium, phosphorus, calcium, sulfur and magnesium.
In addition to these, your plants will also need access to micronutrients, so named as these are needed in much smaller quantities. The micronutrients include boron, copper, iron, manganese, molybdenum and zinc.
If you're growing in soil, your plants will get their nutrients from fertilisers, as well as the natural composition of the soil. In hydroponics, your plants will most likely get their nutrients from a premixed nutrient solution and additives.
There are many reasons why your plants could suddenly start displaying symptoms of a nutrient deficiency and poor health. We'll be going through some of these major causes below.
Plant pests and diseases can cause many issues for your plants, and some of these will alter the visual appearance of your plants. Before you assume that a nutrient deficiency is the culprit behind your plants' unhealthy appearance, it's worth looking for any clues that you might be dealing with a pest or disease instead.
Some pests can cause worrying symptoms, such as holes in leaves or dried, discoloured leaves. These pests include cabbage worms, spider mites, whiteflies, cucumber beetles and other types of worms. The easiest way to identify pests is to do a visual examination of your plants, looking out for the pests themselves, as well as other visual clues, such as insect eggs or bite marks.
Each pest will have their own prevention or 'treatment' method, so it's best to do your research or contact your local grow shop once you've identified the pest you're dealing with.
When it comes to plant diseases, many of these will also affect your plants' appearance. You may see things like yellowing areas on your leaves, dark spots, wilted leaves, stunted growth, necrosis or holes in leaves. Some of the most common plant diseases include mosaic virus, grey mould, bacterial spot or blight and angular leaf spot.
All of these will have different causes as well as different treatment methods. Since these diseases will have their own symptoms, take a look at a disease guide (see further resources below) to help you identify the right one. If you're having trouble identifying the disease that's affecting your plant, it may be worth calling in a plant health expert or taking images of your affected plants to your local grow shop.
This section is only relevant to those growing in soil or potting mixes, but there are a few things to keep in mind.
Firstly, you should check that you aren't over- or underwatering your plants. Some symptoms, such as leaf discolouration or stunted growth, could be caused by soil that is waterlogged or too dry and compact. Either of these conditions would make it much harder for your plants to get the nutrients they need and could lead to other plant health issues as well, such as root rot in the case of waterlogged soil.
Secondly, it's important to know that the natural nutrient composition of your soil will change over time, where certain nutrients may become depleted with subsequent crops. Much of this comes down to the type of soil you've chosen as your growing medium, as each of these will have their own properties, such as drainage and the ability to withstand weather extremes, as well as their natural ability to hold or lose particular nutrients. In addition, certain types of soils can be more acidic or alkaline (see our section on pH below), which will also have an effect on nutrient uptake.
If you're growing commercially, it's critical that you commission a soil analysis before planting an expensive crop. This will help you understand the nutrient composition and properties of the soil you're working with and to identify any necessary treatments or additives that could be used to improve the overall balance.
No matter how you choose to grow, the water you use can affect your plants' overall health. That's because both your water's quality and its contents can have an impact on your crops.
On the one hand, water can contain contaminants, and these can cause an array of issues, such as reducing irrigation flow and inhibiting the control of pathogens.
On the other hand, if you're using municipal water, such as hard water, this may already contain certain nutrients like calcium and magnesium. If you're making use of premixed nutrient solutions, these additional levels of nutrients in your water could cause imbalances and, potentially, a deficiency or toxicity. In addition, the extra calcium increases the risk of calcium sulfate precipitates building up, which could cause equipment blockages.
As with your soil, it's a good idea to commission a water analysis. This could help you prepare for and avoid potential plant health issues, such as a nutrient deficiency, as well as help you consider alternative options, including nutrient mixes for hard water or water treatment processes like reverse osmosis or deionisation.
For more on water quality and its effect on plant health, take a look at our further resources below.
Temperature can also have an effect on your overall crop health. If you'd like to know more, we cover root zone temperature extensively in our guide on pH, EC and temperature - measuring and adjusting your fundamental parameters.
In a nutshell, temperature - specifically your root zone temperature - can affect your plants' ability to reach optimal health. This is due to the fact that two critical chemical processes take place in the roots of your plants: water and nutrient absorption. You need to have the correct root zone temperature in order for these processes to occur efficiently.
Root zone temperature particularly affects the rate at which your plants' roots are able to absorb the nutrients they need. If your root zone temperature moves out of an optimal range - we recommend 18 – 22 °C (65 - 72 °F) for your nutrient solution or irrigation water - this means that your plants' roots will be unable to deliver the appropriate levels of water and nutrients to the rest of the plant.
In addition, root zone temperature can impact oxygen availability and solubility. If it's too warm, you could risk starving your roots of oxygen as warm water cannot hold as much dissolved oxygen as colder water. If the root zone is too cold, this could shock your plant roots, decrease plant metabolic rates and stunt plant growth.
You can easily check your root zone temperature with a handheld meter or pen; we recommend that you measure this parameter on a regular basis so that it never climbs outside of the optimal range for your plants.
Since you're probably already worrying about a nutrient deficiency if you're reading this post, it should seem like a no-brainer that you would take a close look at your nutrient dosing.
No matter how you're growing your plants, you need to make sure that you aren't over- or underfeeding them. Either of these situations will lead to a range of symptoms, such as scorched-looking plants or slow, stunted growth.
The way you check nutrient strength is to measure a parameter called electrical conductivity (EC). EC measures the total amount of food (or nutrients) that is available to your plants. We've already mentioned that your plants need access to nutrients, but these will only become available for absorption in the form of ions. Nutrients become ions when they've dissolved in water, and each of these ions carry an electrical charge, which creates the potential for electricity to move through that solution.
While measuring the EC won't tell you the composition of available nutrients, it will give you an idea of the strength of your dosing. Each type of plant will have a preferred EC range in which it will thrive; outside of this, you could start seeing symptoms of poor plant health. Some plants also have different preferred EC ranges depending on where they are within their growing cycle. This is why it's so important to do your research before planting a particular crop.
You can measure EC using an EC pen or meter. If you're using organic fertilisers in soil, keep in mind that these take time to break down into nutrients. Nevertheless, this is another parameter you should check on a daily basis, as this value will fluctuate regularly.
For more on EC and how to lower or increase it, check out our guide to pH, EC and temperature.
Potential Hydrogen (pH) rounds out our trio of fundamental parameters that you should be checking on a regular basis.
In terms of how it affects plant health, the pH of your growing environment determines whether nutrients will be available to your plant for uptake. pH is a scale that's used to determine the acidity or alkalinity of a solution or substance. A measurement of 0-7 is considered acidic, while 7-14 would be alkaline; a pH of 7 is considered to be neutral.
Each nutrient will have a preferred pH range in which it will become available to your plants. Outside of this range, it will be locked out from your plants, which may lead to a potential nutrient deficiency or toxicity. You can see all the major nutrients, as well as their optimal pH ranges, in the chart below.
Although each plant species will have their own optimal pH range as well, we generally recommend a 5.8-6.5 pH range for those growing hydroponically, or a 6.5-7 pH range for those growing in soil.
Soil has a natural buffering ability when it comes to pH, but using certain fertilisers or additives could create vast changes when it comes to acidity or alkalinity. When you're growing hydroponically, there is no buffer, so there's far less room for mistakes. Either way, regularly measuring pH with a pH meter or pen should be high up on your list of daily growing tasks.
For more on pH and how to increase or lower this in your growing environment, check out our guide to pH, EC and temperature.
As this article demonstrates, there are a number of potential causes when it comes to your plants showing signs of poor health. It may be tempting to simply jump in and treat the deficiency that most closely resembles the symptoms you're seeing, but it's important to ascertain whether there might be something else going on, such as incorrect pH or a compromised water supply.
However, if you're growing a cash crop, it's never worth taking a gamble when it comes to your plants' health. In this case, you should call in a plant health expert to come and assess the precise issue so that you can tackle this effectively.
If you'd like to know more about any of the factors we've covered above, here are some of our favourite resources: