Why are my Chilli leaves turning yellow?

Looking into yellowing

Even with the best care in the world, when growing Chillies, you will always have some new mystery appearing out the blue. For me, the latest is that a couple of my seedlings have developed yellow leaves. It is a bit strange, as it only involves three plants and has only happened in one growing station. It’s time to look into why this has happened.

My research has revealed that the causes of leaves turning yellow are wide and varied. Yellowing of leaves can be caused by factors such as nutrition, watering, disease, pests and temperature. Judging by what I have read, I don’t think it is disease that has caused the yellowing on my plants. On my plants, the leaves are yellowed on the outside. They are otherwise quite healthy. With diseases, it seems you need to look for a yellow to brown mottling and leaves to be wilting. Examples of these diseases are bacterial leaf spot, wilt and phytophthora blight.

Luckily, none of my plants have any of these symptoms, so I could only believe it had to be something else.  The only way to reach a final conclusion was by a process of elimination.  I examined each of the remaining potential causes and arrived at what I think is a logical finding. Here’s how I did it

So what else could it be?

Causes of yellowing

The first thing I looked into is pests. Aphids can cause yellowing of leaves. Again, I don’t think this is the cause.  Aphids are a constant problem in Chilli growing. They are something I have to deal with all the time. I believe however, while I am unable to stop them completely, I do have a reasonably robust way of keeping them under control. At least once a week, I completely submerge my seedlings in a mixture of water and an aphid control concentrate that I recently started using. It seems to work reasonably well

The next thing I considered is fertilisation.  I doubt it is the cause. I feed my seedlings with Chill Focus, which has been diluted to half strength. Where the manufacturer recommends feeding young plants with 5ml per litre of water, I cut that in half to feed my seedlings until they are potted on for the second time. It’s not good for seedlings to give them too much fertilizer. I believe this half concentration is all the seedlings need in their development.  They are currently only two inches tall. When they get to four inches, my same size as pot rule will apply, and they will be potted on for the second time.

So, that narrows it down to watering and temperature.  It must be one of the two. I somehow doubt the problem is temperature related. At this time of year, my main concern is keeping the seedlings warm enough. For them to thrive, they require a temperature of between 20 and 25 degrees Celsius. They are in a grow tent and are kept warm with a tubular heater and heat mats, so can’t see that is the problem.  I monitor the temperature in the grow tent, and it seldom exceeds 23 degrees Celsius.

My suspicion is it comes down to watering. I have had a few occasions gone a bit far with letting the soil in certain pots dry out before watering.  The result was that the seedlings started wilting. I did this because I had overwatered the soil and wanted to dry it to cure the problem. Unfortunately, it meant I went from one extreme to the next. This probably put the seedlings under stress, and they have shown their displeasure by turning yellow

Finally

According to my research, the condition is called Chlorosis. According to some sources, it may also be caused by watering plants with tap water, particularly when chlorine levels are high. Just recently, I switched to only using rainwater or purified water to water my plants, so if this was a contributing factor, I have that one sorted

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Dealing with ailing seedlings

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