Most lawns could benefit from an application of fertilizer twice per year (spring and fall). However, fertilizer is especially important if you notice signs like sparse growth, thinning patches and dead blades. Many people notice their yard is getting sparse in places where they didn't know there was any problem. You may also see an area where your grass looks duller than other parts of your lawn. Patches can become dry or brittle with no signs of new life emerging from below ground level. If you don't apply anything, then these areas will just get worse - until eventually, the grass dies.