Photograph © Kerry Michaels
A friend of mine, who is brilliant, accomplished and lovely, has absolutely no sense when it comes to plants. She claims it's her thumb that is the killer, but I don't think so. As a former plant slayer (ok, I currently have a few dead ones in my driveway), I speak with some authority on this topic.
You have to learn how to take care of plants and want to spend the time it takes paying attention to them and meeting their needs. I have to admit that this isn't always fun. Plant care is not (usually) rocket science, though it definitely is based in science, it is also art mixed with intuition and salted with love. More than anything though I think it is paying attention.
If you are growing plants in containers, I can not stress enough the importance of feeding them. There are some exceptions (most herbs), but most plants and I will hazard a guess that all annuals (ok, there are exceptions like morning glories and nasturtium) need to be fertilized and it needs to be done fairly often. It is hard to write general rules about feeding your plants because it depends on if you mixed a slow release fertilizer in with your potting soil. But here is a rule of thumb--feed your plants with a diluted liquid fertilizer every other week.
But back to my friend. She planted her tomatoes without using any fertilizer at all. Just stuck them in an pot and hoped for the best. I think I'll sneak over there and feed them.