One of my favorite sayings is “nothing in life is simple anymore.” Fertilizing, in my opinion, definitely applies but if you understand the basics, it becomes easier.
First of all, if you put lots of organic matter into your soil before planting and add more every year or two, your garden probably looks great and doesn't need extra fertilizer. For example, if you fertilize a tall sedum, it can make the stems weak and floppy so the plant falls open in the center. Applying the wrong fertilizer won't help your plants much either.
It is best to have your soil tested to determine what fertilizers your soil in general needs. Purdue publication HO-71-W, "Collecting Soil Samples," explains the "how to" of soil testing.
When buying fertilizer, start by reading the label. Every fertilizer has three main ingredients listed in the following order: (N P K) N=Nitrogen which feeds foliage, P=Potassium which produces flowers and fruit, and K=Phosphorus which keeps plants healthy and strong. Different combination strengths are available and what your plant needs will determine the best fertilizer. If you're unsure of how much fertilizer to use, you can start with half or less of the recommended rate and see what happens. Water-soluble fertilizer gives quick results and if there is improvement, feed the plant a little more the next time.
When to fertilize: You can use water soluble fertilizers all season about every two weeks starting in the spring. However, you should use granulated fertilizer more sparingly. You should stop feeding about mid-August as the plants slow down for winter.
Appling fertilizer: Liquid and granulated are the two basic options in applying fertilizer. Liquid fertilizer works very well for annuals and vegetables because it's absorbed quickly through the roots and leaves and rarely burns leaves. The drawback is that it needs to be replaced often because it flushes through the soil quickly. Granulated fertilizer is easy to broadcast and since it releases slower and does not need to be applied as often. Granulated is an easy feeding choice for trees, shrubs, lawns and perennials. Granulated fertilizer can burn leaves if applied too heavily and needs moisture to work so must be applied right before rain or watering. It can also damage roots if it's left in the soil dry.
If you're unsure how much your plant needs, start with about half of recommended amount and see what happens. If there is an improvement, feed the plants a little more next time.
For more detailed information on fertilizing look up Fertilizing Garden Soils.Cornell.edu on the internet.
Purdue University Extension Service can be reached at 499-6334 in LaGrange County.