One question that gets asked time and time again here on the Chilli King is why are my chilli plants turning yellow? There are a number of possible reasons listed below that can cause yellow leaves. As is often the case with diagnosing problems it is usually impossible to say definitively what the
One of the most common causes of yellow leaves on chilli/pepper plants is a lack of nutrients, particularly nitrogen. Yellowing of leaves is more common when growing peppers in pots as there is only a finite supply of nutrients in the soil or compost you used when potting the plants. In order to maintain strong growth throughout the season and maximize flower and fruit production you’ll need to regularly feed you plants.
As a general rule you should feed your chilli plants once a week as soon as they start producing flowers. While you can buy feed specifically formulated for chilli plants such as Chilli Focus which is great I tend to use regular liquid tomato feed. I water it down to half the recommended strength and feed my chilli plants once per week.
Chlorine in Water
Water from a domestic tap will almost always contain small amounts of chlorine which can cause yellowing of leaves. If you can, try to use rain water to water your chilli plants as this will be chlorine free. If you’re unable to hook up a water butt to your guttering then the easiest way is to let the water you use from the tap stand for 24 hours before being used on your plants. Letting the water stand will allow the chlorine to burn off and evaporate making it much more palatable to your plants.
Yet another cause of yellowing leaves may be over watering. Over watering can wash the nutrients out of the soil around the roots. I think a lot of people over water their chillies. As well as encouraging pests, fungus and diseases over watering can also reduce the heat levels in plants.
Even if the top of the pot looks dry if you stick your finger in the soil you’ll be surprised how moist the compost can be just a few centimeters below the surface. The best method I use to see if my plants need watering is to lift the pot and gauge the weight of the plant/pot. Do it every day and you’ll soon get a feel of when the plants are very dry and in need of a water.
Chilli plants are resilient plants and thrive in warm climates with minimal rainfall. I am a firm believer that it is better to under water chilli plants as opposed to over water them.
I’ve also noticed that plants which I leave outside at night tend to be more susceptible to yellowing leaves. Chilli plants love warm temperatures so don’t take too well to drops in nighttime temperatures which can be all to common here in the UK, even in the middle of Summer. It may be a bit of a pain but I now tend to move all of my plants inside each evening and then put them out again each morning!