One of the 5 strains of heirloom tomato seedlings have a leaf problem

by Cindy Whiting
(Quesnel, BC, Canada)

Q. My tomatoes are about 8 weeks old. Just one variety has an issue. First, the veins in the leaves are drying up and then the leaf itself curls. These plants are clearly smaller and weak looking than the other varieties. I start and grow my seeds in coir and feed with diluted Miracle Gro once a week. Soon these plants are being moved into my greenhouse. I wonder if I should separate these particular problematic tomatoes from the other healthy ones?

A. Yes, separate them to be safe.

You didn't mention what tomato variety is affected. As you may know, different varieties have different vulnerabilities. So it may be difficult to diagnose specifically the issue.

Having said that, there is some information that can be helpful.

Dried leaves on tomato seedlings. Drying leaves on tomatoes, even seedlings, can indicate under-watering or over-watering. Specifically, tomatoes grown in coir need extra monitoring. Coir's naturally-aerated structure let it hold up to 8 times its weight in water. Yet because the material is fibrous, moisture drains well to the bottom of the container. Plus, the affected variety may need a bit more (or less) water than the others.

Tomato leaves are curling. Whiteflies (or other sucking insects) can remove nutrients and cause leaves to curl downward. Treat with an insecticidal soap, like Safer Insect Killing Soap. Curling can also be caused by a virus, but because seedlings are grown in a sterile medium, viruses are not the likely cause. Leaf roll or leaf curl can also develop in cool, wet conditions.

Stunted growth on tomato seedlings. Three big culprits are most often responsible for this condition: cold temperatures, inconsistent temperatures, and nutrient deficiencies. Your affected tomatoes are in the same location as the others, meaning they are in the same temperature. They are also receiving diluted fertilizer. But double check to see if they're in a draft or by a window. Even a small difference in temperature can impact a plant's growth.

Hope this helps. Good luck and happy gardening!
Your friends at Tomato Dirt