So why do my tomato leaves turn yellow and why are my tomatoes rotting before they are ripe?
Vegetable season is in high gear and fruit is beginning to ripen. This is the time when I start to get all the questions. Why do my zucchini drop off? Why won’t my melon set fruit? What are those worms on my peppers? I had been working on a post to address one of the most common ones on tomatoes, Tomato End Rot when I got the following question from a reader who purchased one of my Growing Juicy Delicious Tomatoes eBook from Rainforth Home and Garden. First I’ll address his question and then finish up with my thoughts on the issue of rotting tomatoes.
Here is the question from Mr. B. Crowder
What causes the base of the leaves on my tomatoes to turn yellow? How can I save the plants?
Here are my thoughts on that Mr. Crowder. In most cases yellow leaves, which begin turning yellow at the base of the plant first are due to one of two causes. Not just with tomatoes but any plant. Usually, when the older/lower leaves turn yellow it is the result of too much water in the root zone. This could be from watering too frequently but most likely it is caused by a poorly draining soil. I won’t get into the details of the plant physiology but plants don’t like wet feet. Monitor the soil moisture closer and things should improve. Tomatoes like about 1” (3cm for my UK readers) of water per week. I try to water mine once a week. Another possible cause is that as the plants get large the upper foliage begins to shade the lower leaves. This causes the lower leaves to turn yellow and drop off. This is natural and not a problem. It might help to cultivate the soil near the plants to allow better air penetration into the root zone and your plants should recover. It’s a little tough to diagnose with a short description so I hope this helps Mr. Crowder.
Of course there are several other potential reasons for yellowing leaves, (fusaruim wilt, tobacco mosaic virus, alternaria leaf spot). If Mr. Crowder wants to send a more detailed description or even a photo I’d be happy to post my thoughts.
Now for a more common problem, TOMATO END ROT
Yes, this even has happened to me.
Tomato end rot starts as a small brown spot on the bottom of the fruit and enlarges to cover the entire end of the tomato. Eventually the tomato just falls off. The root cause (pun intended) of brown rot on the end of tomatoes is low calcium levels in the plant. The most common cause of irregular calcium uptake is an uneven watering schedule. If you are watering like I advise, consistently and evenly, 1”(3cm) per week you should be okay. A good mulch layer will help even out the soil moisture levels; if you’re already using mulch, you may need a deeper layer but 4” deep maximum.
Take heart in the fact that tomato end rot will not spread from plant to plant and this problem is usually more prevalent on the first few tomatoes. As subsequent tomatoes grow they are less likely to have end rot.
Don’t think you can just spray a chemical and the problem will go away. Since low calcium is the culprit, the use of fungicides or insecticides won’t help.
You could apply a fertilizer that is high in phosphate and low in nitrogen. (3-12-3) That will help the calcium in the soil release better for uptake into the plant but chances are the plant will outgrow the problem. Next season add some well composted organic matter and some of the high phosphate fertilizer and you should be fine.
I hope this helps.
Here are a couple of other posts on tomato problems that you may find helpful too.
FYI these are all covered in my eBook Growing Juicy Delicious Tomatoes.