Starter fertilizer for lawn: when to use it and when not to

What makes starter fertilizer different

A starter fertilizer supplies the nutrients seedlings need to establish quickly. Penn State Extension says many starter fertilizers have equal amounts of nitrogen, phosphate and potash, and others have two parts nitrogen to one part each of phosphate and potash. Examples of analyses are 10-10-10, 16-8-8 and 20-10-10, and most starters contain quick-release nitrogen.

The difference you will notice on the bag is the middle number. A routine lawn fertilizer in many states has a zero there, which means no phosphorus. University of Maryland Extension says maintenance formulations are phosphorus-free, except for starter formulations meant for new lawns.

When to use it

Apply starter fertilizer just before or just after seeding, Penn State Extension says. In Pennsylvania, the optimum times for seeding are mid to late spring and late summer to early fall. The same advice holds for renovating a poor lawn with a seeder that cuts small grooves: apply starter just before or just after seeding.

For spring-seeded fescue, University of Maryland Extension advises a starter with about 50% of its nitrogen in slow-release form. Its guidance is to fertilize according to soil test results at the start; that first application lasts about 6 to 8 weeks.

Overseeding a thin lawn is a gray area. Maryland's law allows phosphorus when a lawn is being newly established, renovated or patched, while the Minnesota and New York rules name only new lawns and soil tests. Whether overseeding counts depends on your state, so ask your state agriculture office before you buy a phosphorus product.

When not to use it

Skip it on an established lawn that is not being reseeded. New York's Department of Environmental Conservation says generally only newly established lawns or those with poor soil need phosphorus, and phosphorus applied to a lawn that does not need it will not be used and can cause water pollution.

Penn State adds that starter fertilizer is not a substitute for the phosphate and potash recommended on your soil test report, so test first. The University of Maryland says laboratory soil tests are more thorough and accurate than home test kits.

Phosphorus rules by state

Minnesota passed the first state phosphorus lawn law, and its Department of Agriculture says that as of 2012 ten other states had similar laws. Phosphorus fertilizer cannot be used on Minnesota lawns unless a soil test or tissue test shows a need, or a new lawn is being established by seeding or laying sod. A zero in the middle of the three numbers is phosphorus-free, and to be labeled zero, a lawn fertilizer cannot contain more than 0.67% phosphate by weight.

New York allows phosphorus lawn fertilizer only when you are establishing a new lawn or a soil test shows too little phosphorus. Its law also bans applying any lawn fertilizer from December 1 to April 1, and fertilizer spilled on a sidewalk or driveway must be swept up, not hosed off. Maryland allows starter formulations that contain phosphorus for new lawns or when test results measure low. Minnesota also requires fertilizer spilled on pavement to be cleaned up immediately, whether or not it contains phosphorus.

Rules change and some cities and counties set stricter ones, so check your state's agriculture or environment department before buying.

How much to apply

Penn State says starter fertilizers should be applied at 0.5 to 1 pound of nitrogen per 1,000 square feet, and that more than 1.5 pounds can burn young turf and cause poor establishment. Maryland's formula for the bag is: pounds of nitrogen wanted divided by the percent nitrogen in the analysis, times the lawn area divided by 1,000.

As an example of that formula, 1 pound of nitrogen per 1,000 square feet with a 16-8-8 fertilizer on a 2,000 square foot lawn is 1 divided by 0.16, times 2, which is 12.5 pounds of product. This is our own arithmetic, so check it against your bag's label. Label rates differ by state: Maryland says lawn fertilizers used there should provide no more than 0.9 pounds of total nitrogen per 1,000 square feet per application.

Starter alone may not carry the lawn. Penn State says that an application of half a pound of nitrogen per 1,000 square feet, 4 to 8 weeks after the starter, helps thicken new turf.