Actually, it is quite easy to over fertilize. How do you know if you've done so?
One of the first things that starts to happen when you've over fertilized is that they leaves start getting a much darker green, even to the point of being a bluish green. They will also start to get a leathery feel to them. The upper most leaves will start to wilt and be limp to the touch. After almost 2 weeks you will notice that the edges of your leaves will start to discolor and look burnt.
So if you have over fertilized, what should you do?
Flushing the soil is about the only thing that you can do, and this does not always work depending on how badly damaged your plants are when you realize they have been over-fertilized. But it is worth giving it a shot.
To flush the soil you will want to first rinse all the plants to be sure there is no residue of the fertilizer on the leaves otherwise the fertilize will rinse off them with the next rain and get into the soil, resulting in a repeat of the over-fertilization of the soil.
You will need a soaker hose. Set up your hose around the soil that has been over fertilized. be sure when you turn on your hose that the water comes out at a rate that allows it to be soaked into the dirt instead of puddling on top of it. Continue watering like this for 10 to 15 minutes. Repeat this process again in 2 hours and throughout the day.