These numbers aren’t just secret plant code, they’re the percentages of nitrogen, phosphorus and potassium! Urea, which can also be present in granular fertilizer, absorbs quickly and is more concentrated, making it very easy to overapply. Your yard, your fertilizer:There is no single fertilizer that is perfect for every lawn, because every lawn is different. The key to knowing the right fertilizer for you is testing your soil. Trees and shrubs usually only require fertilizer in the spring if they appear unhealthy or are growing very slowly.