Tomato troubles

By Don Davis
Published: July 8, 2008

Tomato plants are the main attraction in gardens this month, and they were the subject of many questions in recent days. Here are some examples.

I have mulch left from last year in my yard. Is it OK to use it on tomatoes and other vegetables? I think it is shredded hardwood.
— B.F., Hurt
Vegetables, including tomatoes, will grow just fine with shredded hardwood mulch. It is what we always use in several of our children’s gardens at local community centers.

My Big Boys, Better Boys, Early Girls and Supersonics have yellow leaves at the bottom near the ground. The plants are mulched, and they have dozens of green tomatoes hanging on their vines. I water them every two days. What’s going wrong?
— D.M., Amherst
You could be watering too much. Clay soil holds water for a long time, and watering once a week is more than enough. Another possibility is fertilizer. Tomatoes stressed by lack of nitrogen turn yellow toward the bottom. A third thing to consider is early blight. This disease starts in June and the first symptoms include a yellowing of lower leaves.

Six of my 250 tomato plants look sick, and I need advice. The tops of the plants are curled and knotted, and down at the bottom they look normal. They have dark green color. The six plants in question are all side by side, not scattered through my garden.
— F.B., Lynchburg
Leaves like the ones you describe could be caused by weed killers drifting on the wind, though I think your plants have a virus disease. More than 30 kinds of viruses can infect tomatoes, and there is no cure available. Your best option is to destroy the affected tomatoes right away, hoping the viruses do not spread further. Most modern hybrid tomatoes carry virus resistance, but it is only for one virus (tobacco mosaic virus). Viruses are spread by aphids, thrips and leafhoppers, all of which are abundant now.

My tomato flowers are drying and falling off, and no green tomatoes are forming. They are growing in big pots, and I gave them Miracle Gro at planting time, followed by 10-10-10 in the middle of June. Why are the flowers drying?
— V.C., Lynchburg
Your plants have a condition called blossom drop. Most commonly, it is caused by hot weather. We had many days with temperatures in the 90s, and that is too hot for tomatoes. Other causes of blossom drop are too much and too little water and fertilizer.

I want to know what to do about blossom end rot. If you can give me some help, I would appreciate it.
— N.L., Amherst
The two things to do are cover the root zone with mulch and water often enough to provide an even supply of moisture. These actions will improve uptake of calcium by tomato roots and prevent blossom end rot.

The leaves on my tomatoes are curling, and I want to know why. They are green but tightly curled.
— A.B., Lynchburg
This phenomenon is called leaf roll. It is caused by too much or too little water. Some tomato varieties show more leaf roll than others.