I have several tomato plants in containers which have been doing quite well until recently. I think my problem is either the high temps (90's with high dew points), watering or nutrition (that narrows it down!) but I hope the experts here can lend a hand and perhaps offer a plausible cause.

I have watermelon beefsteak, org delicious and fireworks, all which are relatively large varieties, as well as a few smaller ones. The problem is the leaves seem to be curling and are getting a bit light in color. They are not withering just yet, but certainly not looking as healthy. I trim the lower leaves off, use a drip irrigation system and leave it running for 15-30 min daily. The water is quite cold. Otherwise, I may use a watering can to coat the topsoil keeping it moist. All the pots have drain holes, they contain potting mix and compost. I mixed in a bit of osmocote on the top layer and about a week ago supplied all plants with some fish emulsion. See attached photos for details. The 2 pics on the right show a lighter shade than the left. Hope someone can determine the issue here. thanks a bunch

The growing method you describe has several possible stress causes in it: containers, containers of unknown size, the growing mix you are using, the frequent shallow watering leading to shallow rooting, keeping surface soil wet causing even more shallow rooting, the feeding regimen you are using, etc.

I would suggest some reading over on the Container Gardening forum here and a review of the 'growing in containers' discussions on this forum since trying to grow in containers is a unique form of growing tomatoes with its own set of needs. The search will pull them up for you to browse through.

For example, common recommendations are containers of 12-15 gallons minimum, soil-less potting mixes only, weekly feeding with a full spectrum, well balanced fertilizer, adding beneficial soil bacteria if using organic fertilizers so they can work (otherwise you need to use synthetics), less frequent but deep watering to maintain consistent soil moisture levels, etc.

From the color in the photographs your plants could really use a good feeding. In a container you can't count on compost for nutrients since there is minimal if any soil bacteria.

Dave