I attended a free tomato class at my local nursery which is called Walter Andersen Nursery. The class was very informative. After the class, two other guys and I stayed to ask the presenter a bunch of questions so it was basically a one on one class. I learned about blight that day and thought that my patio tomato had it. I took this picture (it’s on top of my worm bin) and brought it into the store to find out what was wrong.
I hope the picture is clear enough for you to see the black spots with some yellow color nearby. It turned out that this was due to over watering. This was also a main theme in the class. They said that we should check our tomatoes in the morning and check to see if the leaves are wilted. If they are, then give them a deep watering and let them go until they wilt again in the morning. I learned that tomatoes will wilt throughout the day as a defense mechanism against sun burn on the fruit and stalk of the plant. This leads people to believe that the tomatoes need to be watered when they probably don’t need to.
I was told that I should be watering tomatoes in the garden about once a week depending on how hot it gets in the coastal San Diego region. For potted plants, it will be more often since the water runs out of the pots. This is definitely not a rule, so check your plants in the morning and decide if they need to be watered. You can also stick your finger into the soil to see how much moisture there is. If it is dry 2 inches deep, then it’s time to water.
I would like to add that during my past 3 seasons of gardening, I have been watering close to everyday and still ended up with monster tomato plants with tons of delicious fruit. So don’t feel the need to change your style if it’s working. I am trying it out this year and you will be able to see the results.
Here is a nice link about Recognizing Tomato Problems