Soil conditions vary from area to area—and sometimes within the same yard. While some soil is rich and fertile, most could benefit from fertilizer. Adding fertilizer to the soil helps promote plant growth as well as the production of flowers and fruits. It can also lead to bigger plants and fruits and vegetables as well as higher yields. When plants receive the right nutrients, they tend to be healthier, stronger and better able to withstand disease and insect pressure. The best time to buy plant food for your garden is when you're ordering seeds and plants. That way, you have it on hand when your need it.