Q. What is the best fertilizer to use in my garden and landscape? There are so many choices.
A. Your question is difficult to answer because it assumes that nutrients alone (supplied out of a bag or bottle) can provide everything a plant needs for optimal growth. This assumption is based on the law of minimums, proposed by a scientist named Justus Von Leibig in the early 1800s.
Leibig (called the father of modern fertilizer) believed that a plant's growth was only limited by the nutrient that was in the shortest supply. Unfortunately, Leibig forgot about the most basic necessity for a healthy plant, which is the soil and the beneficial microorganisms in the soil for the plant to grow. Adding fertilizer to a plant that is grown in poor soil is like adding seasoning to a poor quality steak burned to a crisp. It's still a steak, but it is just not very good to eat.
You never can go wrong using compost or composted manure as a fertilizer for all your crops. Finding a source of good compost or composted cow manure can be tough unless you make your own compost or know of sources of this material. Don't buy pre-filled bags of this stuff as the actual amount of material in the bags is minimal. One exception is bags of worm castings, which are available at some garden centers or nurseries. With that, you put about 1 to 2 inches of castings, fresh compost, or rotted manure around the plants or on the garden twice each year.
Even mulching with rotted leaves leftover from last year will do wonders for plants this year.
In theory none of these materials should work because the composition of actual nitrogen, phosphorus, and potassium is quite low compared to conventional fertilizers sold at the stores. There are countless studies that show that these natural materials do in fact work very well. This is because the microorganisms contained in these materials work with the soil and the plant to enhance growth. Think about it: Forest trees, for example, drop leaves in the fall which recycle nutrients back to the tree as they slowly decay, no extra fertilizer needed.
This doesn't mean that I don't use conventional fertilizers sold in larger bags at the garden centers, especially for larger areas where it is not as practical to use natural organic materials.
I use either 10-10-10 or 12-12-12 (the numbers are usually on the front of the bag) fertilizer for larger perennial garden areas or lawn. Use two to three actual pounds of dry fertilizer per 10-by-10-foot area of garden or lawn.
You can weigh it out on a bathroom scale, or you can fill a third of a 11.5-ounce coffee can (the smaller cans for real coffee) and scatter over a 10-by-10-foot (100-square-foot area)
There are countless ways to fertilize garden plants. I try to use more natural materials when I can for a more sustainable garden.
The Plant Medic, written by Ricky Kemery, appears every other week. Kemery retired as the extension educator for horticulture at the Allen County Purdue Extension Service. To send him a question, email firstname.lastname@example.org.