Why does Weed'n'Feed granular turn my lawn black on application?

Hi Marie,

The active ingredients in the Weed n Feed Granular are sulphate of iron and sulphate of ammonia. When applied to a moist lawn area in which there are weeds and left for 2 days, the iron has a salt burn effect so that the flat weeds receive a relatively severe burn compared to the vertical blades of grass. After 2 days of having the product on the leaf blade you will notice a black tinge to the grass. After a thorough watering you will find the grass will green up again in about 5 days. Hopefully it will rain, which will certainly help to green up the grass in a shorter period of time.