Even though they are grown in healthy soil and possess stout, sturdy stems, some perennials still need supports to help them stand tall and look their best. Delphinium, Digitalis, and Thalictrum are examples of plants that need staking to prevent them from crashing in high winds or strong thunderstorms.

Fertilizer supplies your plants with mineral nutrients, an essential component of their diet. These nutrients are "fed" to the plant through the soil. Plants growing in soils that do not contain all the necessary minerals show nutritional deficiency symptoms such as yellow leaves, floppy stems, or brown leaf margins.

Nitrogen, phosphorus, and potassium are the three big soil minerals and are called the major elements. They are followed by three minor elements -- calcium, magnesium, and sulphur -- and eight trace elements, which as their name implies, are required in only trace elements.

Most commercially available fertilizers contain only the three major elements packaged with inert filler. You can tell the proportions of each element by the number on the label. Thus a 10-10-10 fertilizer contains 10 percent nitrogen, 10 percent phosphorus, and 10 percent potassium. A 5-10-5 fertilizer, on the other hand, contains 5 percent nitrogen, 10 percent phosphorus, and 5 percent potassium.

It's easy to get stumped when deciding which nutrients to add to your soil since nutritional deficiency signs often resemble signs of disease. Furthermore, although nitrogen is essential for foliage growth, too much nitrogen can inhibit flower development.

In other words, fertilizer cannot be applied haphazardly to garden soil. When starting a new garden, have the soil tested by your county extension agent and get expert advice on just what essential nutrients need to be added. Once these nutrients have been incorporated into your soil, add generous doses of organic matter (compost) as mulch and sidedressings throughout the growing season. These steps should help keep your soil fertile.