Plow & Hearth
Vegetable leaves turning white

Are your vegetable leaves turning white? That is a little disconcerting, yes? White is definitely not the color you are expecting or desiring from your plants! We want them a nice healthy, bright green right?

Why are plant leaves turning white?

There are a couple reasons why your plant leaves turn white. It only comes down to a few reasons. I will give you the summary version here then we will go into more detail below. One. Your plant could have a fungus. Two. It could be sunburnt. That is about it. See. Simple answers. Maybe not so simple fixes.

Fungus (Powdery Mildew)

There is a fungus called Powdery Mildew. It actually just developed on my rosemary. I thought it was dust from building the new greenhouse-but I was wrong. It was doing fine until I moved it into the greenhouse-where already (it is February) that little room is getting humid and toasty.

The mildew is easy to spot because it is bright white and you can actually wipe it off with your finger. And NO plant is immune to it. Good news first. It is rarely fatal to the plant. Yeah! The downside for me is I want to cook with those rosemary leaves-which are now covered in white mildew. 

If you allow the mildew to go too long, your leaves will turn yellow or brown and curl. I discovered in my research that mildew is formed when the humidity is high <Waving my hand right here>, light is low, temperatures are moderate <Another hand wave. It has been around 70-75F.> and the vegetation is dry.

Why are plant leaves turning white

Rosemary with Powdery Mildew

The first thing I did was move the rosemary container out of the greenhouse and into an area that gets good circulation. It actually already looks a little better to me. The pic on the right is the improved look. Was pretty bad a few days ago. In other words, make sure your plant is getting plenty of air circulation.

Your vegetable also needs plenty of sun. Like six hours or more. If it is planted in the ground, can you trim trees and shrubs around it? Try to get it a few more hours of sunlight?

Additionally, be careful you do not fertilize young plants with too much nitrogen. This makes them more susceptible. Consider using instead a time-release fertilizer or compost tea.

Your Plant Has Powdery Mildew Right Now

Do not wait too long before addressing this issue as there are not many cures for it after it has taken over. You can cut off the offending plant parts and/or use an organic or homemade fungicide (more on this below).

That’s it. I realize it’s not much of an answer but Powdery Mildew cannot really be cured. However, it can be managed as long as you proactively monitor it.

Prevention of Powdery Mildew

plant leaves turn white

· Fertilize your plants with compost tea.

· Find plant varieties that are resistant to the fungus.

· Make sure you are planting in sunny areas. (Remember at least six hours each day is optimal.)

· Space plants based on recommendations on seed packets or best practices. Actually, plant crowding can be a major factor in the development of Powdery Mildew and other fungus.

· Prune. It will give your plants breathing room.

· Spray fungicide regularly.

Natural/Homemade Fungicides

As a preventive method, spray natural fungicides on them. For example, Potassium Bicarbonate

why are my vegetable plants turning white

I did not bring up Neem Oil as I have read mixed results on its effectiveness. Now, baking soda mixed with liquid soap and vegetable oil like in the YouTube video below is supposed to be quite effective if you catch the fungus right away-or want to use it as a preventative!

This is something you will have to do on a regular basis throughout the growing season.​


Sunburn (Sunscald Injury)

why do plant leaves turn white

Why do plant leaves turn white? Maybe they are sunburnt! The main reason this happens is the plants were not hardened off long enough before planting outside. In other words, they were not given enough time to acclimate to your sun before being put out there permanently.

And do not assume that because you moved a plant from a greenhouse to the outside it did not need acclimation time. Actually, it did. Greenhouse panels tend to filter UV light whereas direct sun has no filter and beats down on the plant just like it beats down on us.

It is not just new plants that suffer from this though. If you have an extended heat wave (looking at you Phoenix!), then those plants can also get too much sun.

What can you do about it after it happens?

Not much. Cut the leaves off and love on the plant until it can grow new leaves.

Put up a UV sunshade as mentioned below.

plants leaves turning white

Prevention

If you know your plants will or are getting too much sun, consider putting up a temporary sunshade that filters the UV light. If these are new plants, start out with baby steps and only give them a short amount of time in direct sun (hardening off process). Over the course of a couple weeks, you can remove the sunshade earlier and earlier until the plants are tough enough to withstand the rays.

Conclusion

Now you know. The two most common reasons for vegetable leaves turning white are mildew or sunburn. With some proactive diligence, both are easy to prevent (says me with my powdered rosemary!). Afterwards, the damage is the damage but neither normally kills the plant-as long as you stay on top of things. Why are my vegetable plants turning white? Now you know!

* Product images sourced from Amazon.com​

Chapin 1002 48-Ounce Hand Sprayer For Multi-purpose Use
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