I have been told that fertilizer is food for my plants, and that plants must have it every day, just as people need to eat every day, is that correct?

This question has been answered in several of Dr. Mittleider’s books, and the short answer is no. But let me explain further by quoting Larry A. Sagers, Utah State University Horticulturist-in-residence at Thanksgiving Point, and Deseret News Garden Columnist, who says it very well:

“Fertilizers are nothing more than the nutrients that plants utilize to manufacture their food. They are not plant food but are minerals that plants use for manufacturing their food. Plant food comes from combining water and carbon dioxide in the presence of sunlight and chlorophyll.”

The mineral nutrients do need to be in the soil, and they must be water soluble, in order for the plants to absorb them through their root systems, but you certainly don’t need to “feed them” every day. Remember that fertilizers are salts – whether from an organic or mineral source – and “adding them when they are not needed contributes to salt build-up in the soil and can kill the plant. Follow manufacturers’ directions. Do not assume that twice the recommended amount will make plants grow twice as fast. It is easy to add more nutrients if needed, but getting rid of the excess is more challenging”.

Mr. Sagers goes on to point out that “Fertilizer will not cure any plant ills except for lack of nutrients. Fertilizer never cures plants that are suffering from poor drainage, insect infestations, diseases, or over-watering.”

The one important thing to be aware of in this matter is that quite often a nutrient deficiency is mistakenly diagnosed as a disease. Such things as Black-heart Disease in potatoes, and Whiptail Disease in brassicas are actually nutrient deficiencies of boron and molybdenum respectively, so you should learn to recognize nutrient deficiency symptoms before dismissing a problem as a disease. The Garden Doctor series is the best source available anywhere for giving you this very important knowledge.