If you have recently transplanted or brought your pepper seedlings outdoors and put them in full sun, their leaves may turn white.
Leaves turning white on pepper plants is usually caused by sunscald – which is quite common with seedlings that have been recently put outside. It is important to harden off seedlings first to prevent sunscald, but sometimes, it still can happen if it's super hot and sunny the day after planting.
Sunscald occurs when tomato, pepper, and vegetables and plants are exposed to the direct rays of the sun during hot weather without first being acclimated to the sun. Sunscald is basically a sunburn.
Pepper plant leaves are particularly sensitive to direct sun after being grown indoors. It's important to harden them off by putting them outside in incremental periods of time so that they can get used to the strong rays of the sun. We like to put ours in dappled shade for a few hours the first day, then move them into the sun for an hour the second day, two hours the third day, and work our way up to a couple full days of sun before transplanting into the garden. This helps the leaves build up "sunscreen" and resistance to the hot sunlight.
All seedlings started indoors greatly benefit from hardening them off! So don't just transplant them in full sun, make sure to work them up to it first!
It's also important with peppers to wait until temperatures have warmed up to at least 50-60˚ F at night before transplanting outdoors. Peppers tend to have stunted growth for several weeks if they are exposed to temperatures below 50˚ F (unless you grow the Rocoto pepper, which likes cooler temps!).
Don't worry, if they do get cold, but don't freeze, they will start to grow again after a few weeks of warm weather. It just takes time for them to recover. So we like to wait until it's really warmed up before bringing out our sensitive pepper plants.
Peppers do best when they get to enjoy a period of adjustment to the outdoor growing environment - so don't forget to harden them off!
Don't OVERWATER Peppers!
Overwatering can cause yellow leaves on pepper plants. Peppers hate wet feet and if their soil is soggy for long, they'll start to droop, the leaves will turn yellowish and pale, and they will stop growing. Let them dry out between watering!
Peppers can also get Powdery Mildew, causing their leaves to turn white:
Pepper leaves turning powdery white late in the season can also be caused by powdery mildew, a common fungal disease that affects lots of plants. Powdery mildew can be caused by weather – and sometimes occurs with warm, dry days followed by cool, moist nights. If your plants are crowded, or if excessive amounts of high-nitrogen fertilizer are used, this can also create prime conditions for powdery mildew. Water at the base of the plants to keep water from getting on leaves, and don't over-do it with fertilizer. If your pepper plants do get the white powdery mildew on their leaves, some people suggest spraying a solution of 1 part milk to nine parts water to help combat it.
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