Thanks for the question.

The change in leaf color from green to red edges and then to yellow indicates that the green chlorophyll is breaking down. This typically is due to the plant being under some type of stress. Usually leaf yellowing indicates that over watering is occurring. However it appears that you’re being very careful in your watering. Dips in temperature can also lead to red and/or purple coloration at the leaf margins. I suspect that you were keeping your geraniums inside over the winter? If by chance you brought them outside too early with respect to overnight outside temperatures, this might have caused these red edges. Clearly one of the most temperature sensitive regions of a leaf would be its outside edges. Overwatering a geranium can also lead to red leaf margins. Nutrient deficiencies also can cause stress in the plant. The following will provide you further information on these and related points:

https://www.gardeningknowhow.com/ornamental/flowers/geranium/geranium-yellow-leaves.htm - :~:text=One of the most common,the plants to dry out.

https://homeguides.sfgate.com/geranium-leaves-turning-red-96380.html

https://www.gardeningknowhow.com/ornamental/flowers/geranium/red-leaves-on-a-geranium.htm

https://www.google.com/search?cs=0&q=How+do+you+fix+red+geranium+leaves%3F&sa=X&ved=2ahUKEwiustDO_b_4AhXNjIkEHUyiDLgQzmd6BAgHEAU&biw=1193&bih=597&dpr=2 - kpvalbx=_Y3qyYuj4KtDXkPIP9aOf0AI16

My suggestions:

1). Assuming that it is practical and feasible, repotting your geraniums would be a good starting point. In so doing, shake off most of the dirt from the roots and make sure that there is a healthy root system.

2). Use fresh potting soil in this repotting.

3). Be sure that the pots are well draining.

4). If you are keeping the geraniums inside, place the pots in areas that are well lit. If you are keeping your pots outside, place them in an area where they are not constantly in bright sunlight.

5). After repotting, use a powdered fertilizer such as Miracle-Gro. However in preparing this, mix the powder in water in an amount of powder that is half that recommended. You don’t want to overwhelm the plants in their new homes.

6). Leaves that are yellow or brown can be removed from the stem. It’s bit trickier for leaves just having red leaf margins. Leave them attached in hopes that the entire leaf will become uniformly green. Be prepared for this not occurring. If no improvement is seen after two weeks or so, the leaves can then be also removed.

Please feel free to get back to us if you have any questions.

Good Luck.

Glad to be of assistance.  Geraniums are great plants.  I have over 50 growing inside and outside my house.

Thanks so much for your advise! 

Susan

Just, please, feel comfortable in getting back to us if you have any further questions.