Everything You Ever Wanted to Know About Nutrient Lockout

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Before I scare the bejesus out of you with a tonne of information you were perfectly content not to know, I just want to clarify something.

Nutrient lockout isn’t that big of a deal for house plants.

If you do a lot of research into it, you’ll come across people monitoring their pH levels continually, with fancy equipment like probes etc.

This is necessary if you’re growing produce, especially if that’s your profession. The rest of us probably don’t need to bother.

That being said, testing the nutrient water before you fertilise isn't a bad idea.

Nutrient lockout affects EVERYTHING in plants, and if you’re banking on your plants producing delicious, aromatic fruits in large amounts, then it’s worth it to invest in 24-hour pH monitors and test your pH every time you water.

But as you probs agree, that’s not really something house plant people need to worry about.

For one thing, we don’t require our plants to fruit at all, never mind in vast quantities.

But most importantly, they don't go through the water that crops do, so you're unlikely to see significant enough change in the pH to warrant testing the pH more than, say, every couple of months.

I never test the pH of my water, though I really should.

I used to check it, but the readings were always spot on so I stopped. My plants didn’t show any signs of nutrient deficiency – happy days.

However, the water in our new house is…different.

It doesn’t taste quite as nice, and it makes my coffee curdle. I’ve been vegan for many years, so I was well versed in which milks I could use in my coffee without it curdling but that’s all gone out the window. I have to buy barista oat milk now. It tastes good but £2.10?? My smoothie soy milk is 50p!

Anyway. I should really check the pH. I have all the stuff, I’m just lazy.

I’ve not noticed any negative changes in my plants, but I’m doing better at caring for them so they’re currently looking pretty good.

What is nutrient lockout?

Nutrient lockout is when you add nutrients to a plant but the plant can’t absorb them because the pH of the nutrient solution is too high or too low.

The water or soil needs to be at a pH of between 5.5 and 7.5 for most plants. Different nutrients are more readily absorbed at different pHs.

For example, some nutrients are fine being absorbed at a pH level of 5, but others aren’t.

If we keep the pH between 5.5 and 7.5 most nutrients will able to be absorbed in some capacity.

It’s not optimal for all of them, but there will be some availability of all of the nutrients.

How do you know if you have nutrient lockout?

Nutrient lockout causes nutritional deficiencies in the plant.

First, you’ll need to be certain that the symptoms are indeed nutrient deficiency. Check that your watering, roots, and humidity are all in decent knick before treating for nutrient lockout.

That being said, treating nutrient lockout isn’t harmful, it’s just…more likely to be something else, especially if you’re new to caring for indoor plants.

The symptoms of nutrient lockout/nutritional deficiencies are:

  • Nitrogen – old leaves yellow first, yellow spreads from the inside of the leaf outwards
  • Potassium – yellow moves from the outer edges in
  • Magnesium – veins remain green, but yellow spreads from the inner leaf to the edges
  • Iron – yellowing of leaf veins

You may also see:

  • Leaf spotting
  • Lack of growth
  • Curled, browning leaves

If you’re not sure if you have nutrient lockout, you can test the pH of your soil and water. If they’re out of the 5.5-7.5 range, you’ll know that nutrient lockout is the culprit (or is imminent).

You can test it anyway, whether your plants show symptoms or not. It’s fun playing scientist.

Be sure to put your sample in a plastic, not glass receptacle. I’m not sure why (and Google won’t say definitively) but a guy on YouTube said it very sternly so…Imma trust him.

How do I fix nutrient lockout?

There are various things you can try to fix nutrient lockout.

Some companies sell microbes and lime additives to help balance your pH, but in house plants, that’s not really necessary.

Instead, you can really thoroughly water your plants with plain water.

Test the water first, and correct the pH if necessary using pH up/down.

ph up/down for use in hydroponics

Water so that the soil is totally saturated. If your plants are in leca, then let them sit in plain water for a couple of weeks.

Test the soil after a couple of weeks, and flush again if it’s still too low/high.

After that, you can add nutrients as normal, but be sure to test the pH. It doesn’t matter how often you feed, if the plant can’t access the nutrients it won’t make any difference.

How do I prevent nutrient lockout?

Test your soil and water regularly. That’s the easiest way.

I currently have one of those pH test kits where you put it in the vial and add the stuff and then match up the colour BUT I might get one of those probes just to make it a bit more convenient.

They're not *super* accurate, but for a casual house plant hobbyist, they're all you need.

Organic farmers rely on natural methods to keep their soil’s pH balanced. They add various microbes to the soil to help keep the pH in the right range.

All added chemicals will affect the pH of your soil, so think twice about using things like hydrogen peroxide and systemic pesticides unless you really need them.

Sphagnum moss is pretty acidic – around 3-4 – so if your pH is too high, try adding some into your soil.

I'm not saying don't use them, but if you're having pH issues and you're using a lot of chemicals that kill the microbiome of your soil...that may be your issue. 

Another thing to do is read the instructions on your nutrients if they’re ones you have to mix yourself. I use the FloraGrow series, and you have to add Micro (purple) first, then ther others, to prevent nutrient lockout. You have to add them to water, you can’t pre mix them, again to prevent lock out.

General Hydroponics 3 step Flora System fertiliser

What’s the difference between nutrient lockout and burn?

Nutrient lockout can cause burn, but lockout is the same as the situation of the plant not being able to absorb the nutrients from the soil/water. Burn is the result of the lockout.

Just to make things a little bit more confusing, burn can also happen when the plant is getting too much fertiliser. They don’t make it easy, do they?

The problem is, even if you water with pH-tested nutrients, over time salts can build up in the soil and cause the pH to increase/decrease over time. Test your soil as well as your nutrients, I suppose is the lesson here.

How long does it take to recover from nutrient lockout?

It’s less devastating in house plants than crops, because you can just snip off the offending leaves and be done. Usually, the next leaf to unfurl will be fine (or the next one after that, depending on when it developed).

Sometimes leaves can recover from nutrient lockout, but it depends a lot on the resilience of the plant and how quickly you caught it. In general, yellow leaves don’t turn green again.

Final thoughts

Tl:dr if your plants look hungry even though you feed them regularly, check the pH of your soil. Just because you’re adding nutrients to the soil doesn’t mean your plant is absorbing them.

There are other benefits to keeping the pH of your substrate balanced, besides nutrient absorption.

I already mentioned the microbiome of your soil, but balanced soil also promotes the growth of things like mycorrhizal fungi, that will act as root extensions for your plant.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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