Best NPK Numbers for Fall?

We have assembled a few links about best NPK ratios below.  Because 99% of lawns in the US do not get soil tested, most agree. Use a balanced 4-1-2 ratio lawn fertilizer.

Unv of IL Ext Office

“Top quality lawn fertilizers contain slow-release or controlled-release nitrogen. Look on the label for slow-release forms such as ureaform, sulfur-coated urea, milorganite, and IBDU. These forms stimulate uniform growth over a period of time and are less likely to burn the grass. However, do not expect the quick green up caused by fast-release forms. Slow-release formulations are more costly but worth the price for the improved health of your lawn.

In early fall use a regular lawn fertilizer with N-P-K ratios of 3:1:2 or 4:1:2. For example, a bag may list 21-7-14 or 32-8-16. Amounts don’t need to be exact but should be similar to the suggested ratios. Hold off on applying “winterizer” fertilizers until late October or early November.”

Unv of TN Ext Office

“Fertilizers with a 2-1-1, 4-1-2 or 3-1-2 ratio provide N, P and K in quantities closer to actual plant needs and are best suited for maintenance applications. An incomplete fertilizer is one that contains only one or two of the primary nutrient elements. If only one nutrient is present, the fertilizer is referred to as a straight material.” 

Texas Ag

“DO use a 3-1-2 or 4-1-2 ratio fertilizer if youelect not to conduct a soil test. A commonexample of a 3-1-2 ratio fertilizer is 15-5-10,while a good 4-1-2 ratio fertilizer is 16-4-8.These ratios generally supply what most lawnsneed, and they won’t dramatically increase thephosphorus levels if it’s unneeded.”

Missouri Ext

For routine maintenance where a soil test or experience indicates no major deficiencies, use a lawn fertilizer with an approximate ratio of 3:1:1 or 4:1:1 or 4:1:2 at recommended rates according to the schedule in Table 1.

NC State Ext

Apply nutrients based on soil testing. In absence of a soil test, apply 12 pound of nitrogen per 1,000 square feet 3 weeks after greenup. Use a complete nitrogen-phosphorus, potassium (N-P-K) turf fertilizer with a 3-1-2 or 4-1-2 ratio (for example, 12-4-8 or 16-4-8).