Growing tomatoes is one of the most rewarding things you can do. There’s nothing quite like the taste of ripe, red tomatoes that you’ve picked from your own garden. However, tomato plants can have certain problems, and one of them is the tomato leaves turning white. Why does this happen, and what can you do to fix it?
Tomato leaves can turn white when the plant is under stress, receives too much sun without being hardened off, has a nutrient deficiency, or is being attacked by pests. There are ways that you can fix these problems, which we’ll discuss in more detail.
This might sound a little odd because tomato plants do like growing in full sun. However, when the plants are young and haven’t been hardened off properly, the leaves can get scalded by the hot midday or afternoon sun.
The symptoms of sun scald include:
- The leaves start turning white at the edges, and eventually, the whole leaf turns white.
- Leaves start to dry up and become brittle.
- Eventually, the leaves will fall off the plant.
How to Fix the Problem of Sun Scald
First, you want to ensure that you harden off any young plants that you’re about to plant in the garden. This includes those you’ve started indoors and any that you’ve purchased from your local garden center.
Hardening off refers to exposing your new plants to full sun in small time increments each day and then gradually increasing the time until they’re out in the sun full time. Here’s the step-by-step process:
- Start hardening off your plants at least two weeks before you want to leave them outdoors permanently.
- Put your plants outside either on a cloudy day or place them in a shady spot for around 2 to 3 days.
- On the following day, give your plants some morning sun for around half an hour.
- Continue to increase the amount of sun exposure by around 15 to 30 minutes every subsequent day. Do this for around ten days or so.
- By this stage, your tomato plants should be able to handle full sun exposure. If you do notice any white spots on the leaves, bring the plants into the shade or cover them with a shade cover in the afternoon.
If the established tomato plants in your garden are showing signs of sun scald, it’s a good idea to provide them with some shade around midday and in the early afternoon.
Powdery mildew is a fungal disease that is often associated with zucchinis and summer squash. However, it can infect tomato plants as well.
The symptoms to look out for are:
- White patches on the leaves and stems that look powdery.
- These patches will spread quickly across your plant.
- You might also notice some black, sooty patches developing, which are the fungal spores.
- Eventually, the affected leaves will die and fall off the plant.
How to Fix your Powdery Mildew Problem
Powdery mildew is one of those diseases that can be difficult to control, especially if it is well-advanced. Prevention is usually better than a cure for this disease. As it thrives in warm, humid conditions, make sure that you only water your plants at the root level and avoid getting the leaves wet.
Here are some ways that you can treat powdery mildew as soon as it appears:
- If only a few leaves are affected, cut these off and dispose of them in the trash.
- Prune off the bottom leaves of your plants to avoid contact with the soil where the fungal spores may be living.
- Another good idea is to mulch around your plants with a thick layer of straw or hay. This prevents any fungal spores from being splashed onto the plants while you’re watering or when it rains.
- Spray your plants with a sulfur-based fungicide. Make sure you do this on a cloudy day so as not to burn the plants. Repeat the application every 7 to 10 days or after it has rained until you have the problem under control.
- If you’re having a persistent problem with powdery mildew in your garden, select mildew-resistant varieties to plant instead.
There are a variety of sap-sucking insects that may infect your tomato plants. This could result in your tomato leaves showing white spots.
To see whether pests are attacking your plant, look for them underneath the leaves, on new growth, and sometimes, along the stems.
The most common pests that will result in white spots forming on your tomato leaves are aphids. These tiny green sap-sucking insects are particularly fond of tender new growth, so you’ll easily see them on the new tips of your tomato plant.
How to Treat an Infestation of Aphids on Your Tomato Plants
Luckily for you, aphids aren’t really all that difficult to get rid of. Here’s what you need to do:
- If there are only a few aphids on your plants, you can effectively hose them off.
- Alternatively, you can spray your plants with a horticultural oil such as neem oil. Essentially, the oil will coat the aphids, and they won’t be able to breathe. Make sure you mix the oil with water as per the recommendations on the pack.
- You can also plant some decoy plants around your tomatoes. These are plants that are highly attractive to aphids and will keep them off your tomatoes. Marigolds are particularly good for this, and they add some attractive color to your vegetable garden.
Tomatoes are heavy feeders, and if you haven’t given them a regular dose of a balanced fertilizer, this may cause the leaves to develop white spots or patches with green veins. A lack of nitrogen and phosphorus is particularly responsible for the whitening of the leaves.
The lack of minerals such as manganese and calcium is also known to cause white spots on leaves. This may be the case if you have impoverished or heavy soils. Soils that consist of heavy clay often tend to bind the nutrients, making them unavailable to the growing plants.
How to Fix Nutrient Deficiencies in your Tomato Plants
Nutrient deficiencies are fairly easy to fix by giving your tomato plants a regular dose of a balanced fertilizer at least once every couple of weeks. Here’s what to do:
- Choose a fertilizer that is specifically designed for tomato plants or other fruiting crops.
- Check the pack to ensure that the fertilizer has an adequate amount of nitrogen and phosphorus as well as trace elements of calcium and magnesium.
- Apply to your plants, following the recommended quantities and frequencies on the pack.
Just like a lack of nutrients can affect the health of your tomato plants and cause the leaves to turn white, too much fertilizer can also be a problem. This is because the salts in fertilizers can build up in the soil and effectively burn the roots. This can especially be true for plants that are grown in pots.
How to Fix Overfertilizing Problems in Your Tomato Plants
If your plants have been subjected to too much fertilizer, the solution is quite simple. You want to drench the soil with water so that the excess salts get washed out of the soil.
Overwatering or Underwatering
Just like you can under or overfertilize your tomato plants, you can also over or underwater them. The idea is to get the balance just right if you want to avoid the leaves turning white.
If your plants are growing in well-drained soil or in a pot with a good quality mix, you shouldn’t have a problem with overwatering as tomatoes can be quite thirsty plants. However, if the soil that your plants are growing in gets waterlogged, it’s likely that they’ll get root rot. Once this happens, there’s not much that you can do to save the plant.
Underwatering your tomatoes is more likely the cause for leaves turning white because, without adequate water, the roots can’t take up the nutrients that the plant needs to stay nice and green. Therefore, with a lack of both water and nutrients, the leaves will start to die off.
How to Water Tomato Plants
The solution to underwatering your tomatoes is fairly simple. You just have to water them more often. However, you need to find an easy way to determine when your plants need water.
Setting a regular watering schedule can be detrimental because it may not supply the necessary water to your plants if and when they need it. But, there is a solution. You need to check the moisture level in the soil. Here’s what to do:
- Stick your finger into the soil at the base of the plant. If the top one or two inches of the soil is dry, then it’s time to water. If the soil is still damp, then check the following day again.
- Alternatively, you can purchase a moisture meter that will tell you whether the soil is dry or damp.