The bottom leaves on my geraniums begin to wilt and then turn yellow and then die. Why is this happening? I only water when the soil dries out and fertilizer once a week. I pinch off the leaves and other leaf develops the same symptoms. Any help would be appreciated. Thanks.
Yellowing leaves are often a sign of a watering issue. There are other possibilities, but watering problems is one of the more common ones so I would always start by ruling that out first.
My guess is too much water--when you say you only water when the soil dries out, are you just looking at the surface of the soil? The surface will dry out fairly quickly, but if you stick your finger an inch or so into the soil you'll probably find it's still quite wet. You need to wait until it's drying out a couple inches down before you water again, otherwise the roots are staying a lot wetter than they want to be. Also if your pot doesn't have a drainage hole, or if you have it in a saucer and let water sit in the saucer after you've watered those can contribute to overwatering as well.
Underwatering also has similar symptoms, although many more people kill their plants with too much water, that's why I suggested it first. But if your plant is a bit too big for the pot it's in, then there might not be enough soil to hold water so it may be spending most of its time too dry.
One other possibility would be too much fertilizer, once a week could be fine or it could be too much, depends on what the package directions are. My guess is if you're using it at the max concentration that's probably a bit much, but if you're diluting it a lot then it may be fine. However, over time fertilizer salts and other salts from hard water, etc can build up in the soil, so if it's been a while since you changed your potting mix that's also possible. Especially if you water by "topping it off" rather than by letting a lot of water flush through the pot, that can make the salts build up faster.
Hopefully that gives you a few places to start. It would also help if you could post a picture, preferably one that shows the wilting/yellowing leaves as well as giving us a sense of the size of the plant relative to the pot.
Just realized that I'd jumped to a conclusion that you had these in a pot...if they're planted in the ground then I still think it's probably a watering issue, but obviously some of the things I said about pots and saucers, etc would not be relevant.
I agree with Ecrane as far as the watering and fertilising goes, the problem may be that you are also allowing water to get onto the foliage and this causes them to go yellow and die off, these plants normally like baked sunlight and the soil to get quite dry before they need watering again, also IF as Ecrane has suggested and they are in pots, have you got a saucer under the pot where the pot then sits in water for long periods as the compost will act like a sponge and stay wet for ages too, good tip also from her is about the compost, has it been renewed before planting as these plants will need new compost every year as the roots will deplete any nutrients that were in the compost after a year of growing. hope all this helps but as Jasperdale has said too, let us know which kind of geraniums are you growing as there are so many, then we could help you further,
good luck. WeeNel.