Fertilizer Shelf Life

Asked April 21, 2017, 8:33 AM EDT

Does fertilizer have a shelf life? Specifically; I have individual bags of nitrogen, phosphorous, & potassium. They are somewhere between 20-30 years old. They have been kept dry. Can I use them? Another question if you don't mind; the last two years our garden has produced apparently healthy plants but without any produce to speak of. Do you think the recommendations will correct this or do I have another potential problem? Thank you for your consideration

Wayne County Michigan

5 Responses

If stored properly (cool and dry) fertilizers can have an indefinite shelf life. However, I would recommend contacting the manufacturer of the fertilizers and ask them. If you had a soil test done, the recommendations will correct soil deficiencies. If not, I recommend obtaining one: www.msusoiltest.com The other factors that can affect vegetable production are disease and insect problems, temperature, moisture and pesticide use. Here is some additional information on vegetable gardening:

Thank you for the quick response and information. I did have a soil test done....sorry, I thought you probably had access to it. Problems are low potassium (85 ppm) and high magnesium (196 ppm). Soil PH is 7.4.
Any further thoughts?

Send me your 6 digit code and I'll review your soil test for further recommendations. Thanks.


The recommendation for your garden is 3-4 lbs of nitrogen, 2 pounds of phosphate, and 4.6 pounds of potassium/1000 sq. ft. Complete fertilizers have all three nutrients in varying concentrations. Since fertilizers never have 100% of the nutrient, calculations are necessary to determine the amount to use. The easiest thing to do is to use a fertilizer that comes close to ratios you need which is spelled out in Option 1, 2, and 3 in your soil test. You mentioned you had individual fertilizers. To determine how much of each you need divide the yearly recommendations by the concentration on the label. For example:

A source of nitrogen only that is commonly sold is urea which is 46-0-0 which means that it is 46% nitrogen. To determine the amount of nitrogen you need: 4 lbs (N) รท .46 (concentration) = 9 (8.7) pounds of urea/1000 sq. ft. per year. Two thirds (6 lbs) are applied before planting and one third as a side dressing in June. Using this formula you can determine the amounts needed for phosphorous and potassium. The phosphorous and potassium can be added all at once before planting.

Your pH is a on the high side for vegetables. They prefer a pH of around 6.5. I would incorporate about 5 lbs of sulfur/1000 sq.ft. before planting for 3 years Refer to the fact sheet available in your soil test report.

Your organic matter is 4.8% (average 4-9%). I would add organic matter (compost, manure) it bump it up little.

Follow the recommendations for 3 years and then repeat the soil test.

Soil is 1/3 of the puzzle. Make sure the garden gets adequate moisture and that it is planted in full sun. Mulching is also very beneficial.