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Yellow leaves on a plant can look beautiful, and I’m embarrassed by the number of times I’ve thought ‘wow, look how pretty tha-‘ and then the leaf drops off.
First things first – don’t panic when you see a yellow leaf. Your plant is not necessarily dying. But this does need to be said:
A yellow leaf on a house plant is unlikely to turn green again UNLESS the yellowing is caused by a nutritional deficiency, which if rectified, could cause the green colour to return.
Usually though, say goodbye to the green. Hell, make your peace and put the whole leaf's affairs in order. Never mind. (Hopefully) there are plenty more where that came from.
Nutritional deficiencies in plants are far more likely to be caused by age or root issues UNLESS you strictly use distilled water to water your plants, in which case, you need to get yourself a hydroponic fertiliser.
What causes a plant’s leaves to turn yellow?
The yellowing of plant leaves is called chlorosis, and it’s caused by a variety of issues:
I have a whole article that goes into detail about why plant leaves turn yellow, and it has a lot to do with root issues, but I’ll whizz through it here too:
If you let your plant dry out too much, the roots will shrivel up and die. The root system is the primary way that plants get water and nutrients, so if the roots are dead, the plant will be soon too. You can re-root the plant and help it recover though.
Overwatering turns the potting medium into oxygen-less mud. As the soil dries out, air pockets form that allow the roots access to oxygen. If the soil isn’t allowed to dry out properly, then two issue arise:
- The roots have no access to oxygen and will die in time
- The anaerobic bacteria that thrive in this environment multiply quickly and cause root rot.
As the soil compacts over time, less and less oxygen is available to the plants, again resulting in an increase in the number of root rot-causing bacteria.
You can add soil amendments to your potting mix to increase the aeration, such as perlite and/or orchid bark.
It might also be that your plant is root bound to the point that the soil and oxygen have been displaced by plant roots, in which case you need to repot your plant in a bigger pot.
If you feel like your soil is only compacted due to the effects of regular top watering, you can use a chopstick (or moisture metre) to fluff it up again – just be careful not to damage the roots too much.
Poor drainage will result in overwatering and therefore root rot over time, so make sure you have adequate drainage:
Plenty of people claim that they have plenty of happy plants in plant pots that don’t have drainage holes, but the cold fact remains that it’s WAY more difficult (if not impossible) to thoroughly water a plant if there are no holes in the bottom.
To avoid overwatering you’d have to measure the exact amount of water you need and hope to spread it out evenly in the soil. Having holes in the pot to allow excess water to drain away is a much better solution.
This serves no purpose other than to create a perched water table in your pot. Gravel can’t hold water – all it’s doing is taking up space that could have been used for potting mix.
You can't use gravel as an alternative to holes in your pots - all that happens is the water will collect at the bottom and have nowhere to go.
The next time you water the gravel-filled reservoir at the bottom will fill up until it reaches the soil and you’ll have a muddy mess.
I usually recommend that we tailor our potting mix to our watering style – chunky for overwaterers, denser for underwaterers.
However, there is a thing as too dense – make sure you use something designed for house plants. Soil designed for use outdoors is much denser because the soil dries out much faster (especially in windy/hot weather).
Don’t assume you have alkaline soil, just because you have yellow leaves – buy a soil pH test kit (don’t trust the ones on moisture metres – buy test strips).
Ideally, soil pH should be between 5.5 and 7.5. If it comes back higher than that, you can add soil amendments like sphagnum moss and sulphur. You can also use an acidifying fertiliser.
It can take a few weeks for the soil’s pH to adjust so be patient.
The most common nutrient deficiencies that cause chlorosis are iron and manganese – both of these may be present in your fertiliser but bear in mind that they are unable to be absorbed by the plant if the pH is too high.
Other common deficiencies that cause yellow leaves are:
- Nitrogen – old leaves yellow first, yellow spreads from the inside of the leaf outwards
- Potassium – yellow moves from outer edges in
- Magnesium – veins remain gree, but yellow spreads from inner leaf to edges
- Iron – yellowing of leaf veins
Not all fertilisers are made the same, and many (especially, I’m afraid, the more natural ones) don’t have a complete of the micronutrients that plants need.
If you’re worried that your fertiliser isn’t complete, you can use hydroponic nutrients, which contain the complete profile of macro and micronutrients that your plant needs.
This is especially important if you water using distilled water.
Most sucking pests can cause yellow leaves as they suck the chlorophyll out of the plant.
Yellow leaves caused by nutritional deficiencies may turn green again
The issue is, as ever, that even with the guidelines above, it can be difficult to ascertain which nutrient your plant is lacking.
In this case, I'd recommend using a hydroponic fertiliser. Soil fertilisers, especially natural ones, tend to only concentrate on the NPK values (nitrogen-phosphorus-potassium) which would be akin to us only considering our macros (fat-carbohydrates-protein) when trying build a healthy diet.
We also need to consider micronutrients, like iron and potassium – and so plants. Since hydroponic fertilisers assume that there are no micronutrients in water, fertilisers contain all of the required nutrients.
If you used distilled water and have been seeing a lot of yellowing leaves, it is likely due to the lack of minerals in the water.
Should you get your plants the nutrients it needs before the leaf is too far gone, then the leaf may very well return green.
If I find the cause of the yellowing leaves, will they go green again?
Errrr, probably not. I’m not going to say definitely not, because if you catch it early enough, you may be able to get some chlorophyll back into the leaf. Chances are though, your plant has already written that leaf off.
In some cases of nitrogen deficiency, you can reverse the damage, but it’s unlikely that you’d catch it early enough.
You can, however, prevent any further yellowing by identifying the issue and rectifying it. Your plant wants to get better, you just have to help it.
By the way, some plants put out yellow leaves at a rate of knots. I have two Philodendron Selloum which ALWAYS have at least one yellowing leaf. They're perfectly healthy, and are putting out new growth, but they're always sacrificing one leaf or another. Has anyone else experienced the same?
I’m not sure if it’s to do with the type of plant because they both had a hairy start in life. One was from a big supermarket and was wrapped in plastic and sat in a draft, and the other I bought from Wilko. As an outside plant. It was outside. In England in October. The poor lamb.