Dear Lee, if it keeps happening it means they are in the wrong soil in the first place! They prefer a peaty (sphagnum moss) soil. The pH is very acid on this.
Try mulching with peat! A lot of people do this and think that by adding chemicals each year they can change what nature out there in the first place, nature will win!
Also a lot of people mistake Chloris of lime for what is magnesium deficiency! Try using Epsom salts at one handful 1 1/2 ounce per sq yard!
Also do not give them tap water!
Regards.
Neil.
