Taking care of potted plants

how long have they been in the pots?

Adding manure once a month may be too much for your plants. I would feed them some epson salts mixed with water maybe once a month. Manure is pretty strong and I would only use it mixed in with the dirt when I first plant.

Are they indoor plants that you bring outside in warm weather? Most house plants are tropical and will not fair well in strong sunlight. They need shade or filtered sunlight.

The size of the pots may be too small for the size of the roots, and, as a result of the roots being cramped in the constricted space, they are unable to properly absorb the nutrients in the fertilizer and the water. I suggest that you transplant the flower plants into larger pots with fresh potting soil.

Thanks Ms.Chubby58 for the useful guidance.

Thanks Mr.Flipturn. Its a very good guidance. I'll transplant as guided by you.

most likely they need re-potting

Plants also will slow down growing when it's too hot. If you transplant to larger pots, try and get lighter colors ( or paint outside of pots) darker colors absorb the sun almost turning your flower pots into cooking pots!