Fertilizer – Mixing Your Own

Q: I had a soil sample from my vegetable garden tested by the Extension service. The resulting report recommended I use ammonium nitrate (34-0-0) and 5-10-15 fertilizer. However, when I went to several garden centers they did not carry the 5-10-15 fertilizer. Where can I get some of this stuff?

A: Fertilizers with a 5-10-15 or 6-12-12 analysis are usually recommended for vegetable gardening. They allow an initial feeding with phosphorus and potassium (the last two numbers on the bag) followed by more nitrogen (the first number) when the garden plants have grown for a few weeks. Urban and suburban garden centers cater mostly to people interested in feeding only their lawn or landscape. The nurseries receive little demand for 5-10-15 so they may not order it regularly.

However, if you don’t mind doing a little mixing, Dr. David Kissel, head of the state soil testing lab, says you can make a fine substitute for 5-10-15. All you need is the following: ammonium nitrate (34-0-0), triple superphosphate (0-46-0) and muriate of potash (0-0-60). Most nurseries have all three.

In a plastic tub, mix a half pound of ammonium nitrate with one pound each of the superphosphate and the potash. The result is a fertilizer with a nutrient analysis of 7-18-24. Notice that the ratio between the three nutrients is close to 1 – 2 – 3….and that is the same nutrient ratio as the recommended 5-10-15 fertilizer (1-2-3).

Now you’ll have a fertilizer of the right ratio…… but it is a bit more concentrated than 5-10-15. No problem: just apply it at one-half to two-thirds the rate you were given on the soil test report.

I’m sorry you didn’t get what you needed the first time but at least now you have a way to mix up what you set out to get.