Flowering annuals such as geraniums are best fed weekly ...at least every 10 days to two weeks to promote continued lush flowering. A 15/30/15 will do nicely.
(Miracle Gro is one such)
If its a particular hot day, water the plant first...then give it the fertilizer liquid.

Geraniums are one of the easiest to divide. Just take the plant out, and with hands, pull the roots apart and plant into fresh potting mix. Water the plant the night before and water immediately after transplating. Your geranium's container should drain well.

Do it on a cloudy day so the plant, once out of its container, doesn't get hit by too much sun or heat.

Jeanie,
Thank you so much. I love Geraniums and will try doing as you stated.
God Bless!
Betty in Florida