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Are You Being Tricked By Nutrient Toxicity?

Date: 16-11-2021

Whether it’s overfeeding the family goldfish or overwatering the lawn, we’ve all been there. No matter how well-intentioned, too much love is exactly that - too much. The same rings true for hydroponic growing. When you increase nutrient dosages, you aren’t necessarily doing your crops any favours, in fact, you could be inadvertently killing them. 

Let’s break this down a little more: 

One of the biggest advantages of growing hydroponically is that you get full control over all your plant’s inputs. Unfortunately, this can equate to more mistakes, especially for beginner growers. 

When you have a nutrient present in your system in a large enough excess, your plant’s ability to absorb other essential nutrients is reduced or blocked completely. This can cause a number of symptoms and it’s very important you are able to not only recognise them but differentiate them from symptoms of plant deficiency and disease. This is because using a treatment to fix a deficiency when you actually have a problem with toxicity will almost definitely make things worse and can even kill your plants entirely.  

If we ran through the symptoms of toxicity for every nutrient, this email would drag on forever. Today, we’re going to focus on macronutrients but stay tuned as we will definitely cover micronutrient toxicity in a future newsletter. 

Here are the signs you should look out for: 


Nitrogen (N): If you could only read one paragraph from this email, this is the one. If you are experiencing nutrient toxicity, nitrogen is likely the culprit. Nitrogen toxicity can show up in a couple of ways. Foliage may be lighter in colour than you expected (especially leaves lower down on your plant as these are usually the oldest). You may also notice stunted growth with plant stalks being shorter and skinnier than expected. Moving down the plant, you may notice a very dense root system. 


Phosphorus (P): Phosphorus toxicity is quite rare, but will usually present as a copper or zinc deficiency as too much phosphorus prevents the plant’s ability to intake these nutrients. Look out for plants with stunted growth and abnormally green or purple pigmentation on the undersides of foliage. 

Potassium (K): Potassium toxicity is usually indicative of stunted growth and small leaves. You may also notice yellowing on the tips and edges of your plant’s foliage. Look out for signs of deficiency in the following nutrients: magnesium, manganese, iron and zinc as the uptake of these nutrients are blocked by excess potassium. 


Calcium (Ca): Calcium toxicity usually presents as a manganese or potassium deficiency. Look out for stunted, unusually horizontal plant growth and foliage that has either crinkled up or formed a rosette. Pay attention to older foliage as well, looking out for white spots near the veins of your plant’s leaves. 


Magnesium (Mg): Magnesium toxicity can be hard to spot but will often look like a calcium deficiency. Keep a keen eye on younger leaves first, as these will be lighter in colour than expected. They may also look a little bit ‘blotchy’ in appearance, and you may see the edges of foliage curling upwards. 


Sulfur (S): Sulfur toxicity is uncommon and presents similarly to nitrogen toxicity. Subtle differences between nitrogen and sulfur toxicity exist and include plant stems that are woodier than they would usually be. You may also notice thicker, discoloured  foliage.

Now that you know what signs to look out for when you suspect nutrient toxicity, we can run you through how to correct it. 

Once you have identified the nutrient that is present in toxic levels, you’ll need to get onto correcting it very quickly. 

Unlike nutrient deficiencies where correction happens slowly, a problem with toxicity means time is of the essence. 

The first step in correcting toxicity is to flush out your system. 

Drain all water from your system and reintroduce pure (pH 7), distilled water. If you’re not able to use distilled water you can use filtered or reverse osmosis supplied water as a second best option. You can add a flushing agent as well if you’d like to, we recommend CYCO Kleanse (we’ll link it below).

Monitor your plants very carefully as you may need to repeat this process due to excess nutrient stored inside the plant. 

If you manage to catch a build up of nutrient quickly enough, your plants should see a full recovery. If your plants are going to recover, you should begin to notice signs of improved health in about a week. 

Once you’re sure your plants are going to recover, you can begin to reintroduce a modified nutrient regime. Start with ¼  of manufacturer prescribed dosage, increasing this by another ¼ each week until you’re back to standard dosage.