I forgot to mention that the containers are 15 gallon and the only pestiside that I've used is insecticidal soap.

The most common cause of yellowing leaves is over-watering especially in containers and especially with poor draining soil. It is by far the common cause. The next most common cause is nutrient deficiency, esp. nitrogen.

Otherwise we'd need to see a picture of the plants and leaves to rule out disease problems. Can you post pictures of them?

Dave

I've been watering 2-3 times a week and am using organic tomato plant food spikes. I have no idea how to post pics on this site...

Sarah

Here's help to post images
http://forums.gardenweb.com/forums/load/hosta/msg0513322013993.html?14

Here is a link that might be useful: how to post images

"Watering 2-3 times a week" can still be too much if the plants don't need it. The soil moisture content determines when the plant needs water, not any set schedule. If the soil down at the root level is kept too wet then the roots rot and the leaves turn yellow. Learn to stick your fingers deep into the soil to check for moisture before watering.

And every time you water the nutrients wash out of the container with the water. Container plants need regular and consistent feedings to replace the lost nutrients. Spikes aren't going to provide that for long.

Organic fertilizers only work if there is enough soil bacteria to convert them to a useable form for the plant. In containers filled with sterile potting mix there is little if any soil bacteria.

Dave

Hello again Dave.
I think your right about over-watering. I just went out and looked at my plants again and the romas, which are in a plastic container, are a lot more yellow than the yellow pears which are in a ceramic pot. Basically when I planted them, I looked on CA Tomato growers website which said that once a tomato plant has fruit on it, it likes a little water every day (which seemed like a lot to me) but I was waiting until top soil felt dry to water (hence 2-3 times a week). Apparently I need to feel farther down into the soil. And the spikes claim to work for 6-8 weeks but they may be over estimating? Thanks for the advice! I've never had a green thumb but I'm trying. So I'll try less watering and more plant food :)