I’ve gotten this question many times: why are my tomato leaves turning white? I grow tomatoes every year and have personally experienced just about every possible problem they can throw at you, including their leaves turning white. The good news is that the most common causes of leaf whitening on tomatoes are easily walked back and fixed. The bad news is that this damage may partially stunt their growth moving forward, so the sooner you can correct the issue, the better off your plants will be. In this article, I’ll break down the reasons why tomato leaves turn white from the most likely to the least likely cause.
Why are your tomato leaves turning white?
There are four primary reasons for tomato leaves turning white. They include planting unhardened plants, exposing tomatoes to cold temperatures, nutrient deficiencies in the soil, and fungal diseases. We’ll take a deep dive on each of these issues and how to fix them if it’s possible to fix them.
Tomato plant not hardened off before planting
Probably the most common reason that gardeners experience tomato leaves turning white is due to not hardening off their tomato plants before planting. Whether you’ve started your own tomato seeds indoors or purchased some from a nursery, they’ve been in a fairly consistent environment – the same temperature and the same amount of limited direct sunlight. If you plant your tomato starts outdoors right away with no adaptation period, the sunlight and temperature variations can cause your plants damage.
Hardening your tomato plants is a process by which you move your starts outdoors for a few hours every day and then move them back indoors in the afternoon and evening. This helps your plants get used to being outdoors.
In the case of sunscald on unhardened tomato plants, my recommendation would be to put something up next to your plants that helps shield them from the afternoon sun. I don’t recommend digging your plants up and moving them back indoors. Doing so may cause irreparable damage.
As gardeners, we’re always eager to get going with our gardens every spring. But something we should all consider is that just because our final frost date has passed doesn’t mean that every plant can go in the ground immediately. Tomatoes are hardy down to 33 degrees Fahrenheit, but they tend not to thrive when temperatures drop below 50 degrees. Tomato leaves turning white in the early spring and late fall are likely doing so just because temperatures at night are beginning to drop.
If possible, you can set up a greenhouse around your tomato plants to increase nighttime air temperatures around them and begin to reduce the damage that’s causing your tomato leaves to turn white. If it’s early spring and your plants are small, you can cut a gallon milk jug in half and place the top portion over your tomato plants to form a makeshift greenhouse.
Nutrient deficiencies turning tomato leaves white
If your plants were properly hardened off and you’re certain that sun and temperatures are not the causes of your tomato leaves turning white, it’s time to move on to the next most likely cause: nutrient deficiencies. Tomatoes, like all plants, need a balance of nutrients in the soil in order to grow. Tomato plants growing in soil that is low in phosphorus and nitrogen may grow leaves that turn either yellow or white. Calcium and magnesium deficiencies can also cause this problem.
Normally I don’t recommend purchasing store-bought fertilizers. I take a more holistic approach to my soil: I don’t till it and I add tons of organic material over the winter months. This results in garden soil that is nutritious and healthy. But if you suspect that your tomato plants are being stunted and damaged by insufficient nutrients, the quickest way to rescue them is by purchasing a tomato-specific fertilizer from your local garden center or nursery. Always strive to use organic-certified fertilizers.
The least common but most challenging reason for tomato leaves turning white is a fungal disease. The most common fungal infection that damages tomato leaves actually isn’t present on the leaves but in the roots. Root rot is an issue caused by excessive water in the soil that allows root-damaging spores to rot out the tomato’s roots.
Provided your tomato plant isn’t too far gone, you can correct root rot. For the first week after planting your tomatoes outside, they should be watered fairly heavily, every other day or so. After that first week, you should reduce watering to no more than once a week unless you live in an extremely hot, arid environment. The soil around your tomatoes can and should dry out just a bit between waterings.
If you suspect root rot, allow the soil to dry out fully for a few days, and then begin a more appropriate watering schedule of about once every week or two. The reduction in moisture will hinder the development of root rot fungus.