There is probably something wrong with soil ph, i think this is the consequence of nutrient lock out. Specifically, curling of leaves upwards and yellowing is a sign of boron deficiency but there could be a lot more going on.
Since i doubt you can change the soil easily, i suggest a foliar fertlizer with micronutrients as first aid. Then try to measure soil ph and adjust accordingly if possible.. This could also be attributed to water shock if you've had a lot of rain, plants would be unable to take nutrients and look like this.

Too much moisture in the soil, causes nutrient lockout and yellow chlorotic looking leaves. Many in North America have been having that problem this year because of the excess rain and cool evenings this past spring + early summer.

Let the soil dry out more between waterings, the plant will definitely green and perk back up afterwards. Might take a week or two before you see results.

A mild shot of ferts "may" not hurt, but that depends on how rich your current soil is. I would hold off just a short while longer though, in my experience plants don't take ferts too well when they are in this over-watered chlorotic state.

Edit: and yank the weeds, they compete a lot more than most people think ;)

This post was edited by sjetski on Sun, Jun 23, 13 at 20:00

Like said above I would let the soil dry out COMPLETELY before watering again. They'll bounce back.

If possible test the soil pH before it is too late. I had similar problem and found it was related to soil pH.

Caelian