Question
We have a knockout rose plant planted in the backyard by previous owner. We stay at Plano (near Dallas), TX. During start of spring this April, it was very huge and we got it trimmed 3 weeks back.

It has been flowering very well, but the buds and the grown up flower is browning at the edge.
Do I need to put some fertiliser? Please I need your help.

Answer
Browning at the edges could be caused by mainly two reasons. One it needs more water or it is tip burn from too much fertilizer or if the fertilizer was applied when the wether was hot. The,last and I think this is the reason, is that there are tiny rose midges in the flower buds. When they hatch they damage the flower buds and when the flowers open they have brown edges or are even dead. Also the flower buds can be totally dead and even dried up.
I would take a bud and break it open and see if there are any tiny white worms in it. If there is then you will have to use a spray for rose midges as there are no organics that will solve the problem. Don't forget to spray all around the base of the rose bush as that is where the adults hide in the ground.
If there are no signs of worms, water very well for a week keeping the area wet to try and flush out any of the fertilizer salts that could be burning the flowers or even solve the problem of not enough water. In high heat a rose will need about 5 gallons of water every five days. That is about one large bucket of water.