One of my sunflower leaves turned yellow and dried since 2 days ago. The bottom leaves became crispy and the top leaves slightly curled. I did watering it daily so I am not too sure is it over or underwatered. I touched the soil on top and bottom it's dried so I assumed it lack of water. I tried gave it additional water and moved it under shade. The other sunflower had same problem yesterday. Most of the bottom leaves dried up within half day, although additional water slow down the problem but I can see the top leaves started to turn yellowish too.

It's flowering soon, how can I save it?

Hi and welcome. Looks like you are trying to grow those in tiny containers with no drainage - A death sentence for a big, lusty plant like a sunflower.

Hurry and pot them up into flower pots about 4 times that size, with drainage holes in the bottom and good potting soil with some fertilizer.

The one with the browning leaves might already be dying from root rot, but the other one looks like you might save it.

They will need at least a 5 gallon pot. With drainage holes. To grow to any size. Fertilizer, and well draining soil, also.

Thanks guys!