Asked August 24, 2014, 10:37 PM EDT
Dubuque County Outside United States
I am not sure I have ever heard of corn cob fertilizer. Typically we refer to natural fertilizers from corn as "corn gluten meal". It on average contains about 9% nitrogen that plants, including fruit trees, can use as nutrients for growth.
Generally speaking, plants don't care where their nutrients come from, because they take up nutrient in the elemental form. Natural fertilizer must be broken down this elemental form by soil microbes before they are available to plants. Synthetic fertilizer are generally already in the elemental form, so they are more readily available to the plant after application.
The misapplication or abuse of fertilizers, whether it is natural or synthetic, is what leads to environmental contamination. It best to have a soil test performed by a reputable laboratory, and base you fertilizer on the results.
In all areas of landscape and gardening, plants will greatly benefit from the addition of fully decomposed compost. The compost provides a greater benefit to the soil than corn meal alone. In addition, the use of hardwood mulch around your plants, including fruit trees, provide a tremendous benefit to plant growth. In our research we have found that many types of plants do not require any supplemental fertilizer when you maintain a 3 inch layer of mulch around the plants. Using recycled yard and garden waste, in the form of compost and mulch is a much more sustainable way to garden.