Just like people, plants have basic nutritional needs. And just like people, they need more of some nutrients than they do of others. Plant nutrients can be grouped into macro nutrients (those they need a lot of) and micro-nutrients (those they need in small amounts). Every package of fertilizer should give its nutritional value. Usually this is indicated by three numbers such as 10-20-10. Those numbers represent the macro nutrients nitrogen, phosphorous and potassium. 10-20-10 means that package contains 10% nitrogen, 20% phosphorous and 10% potassium by weight.

Why do annuals and perennials have special fertilizing needs when plants in nature get along without it?
In nature, plants rely on sunlight, rain and the nutrients in the soil. Nature limits the types and numbers of plants by the relative amounts of these basics available. In our landscapes, we grow many plants together with differing requirements, often in a variety of types of soil, surrounded with competing grass. If they are to thrive, we have to supplement what nature can provide.

What makes fertilizing annuals and perennials any different than fertilizing any other plants? In our climate, all plants are either herbaceous or woody. Woody plants have parts (such as trunks, branches, twigs, and in some cases evergreen needles or leaves) that live from season to season. These give them a big head start each year. Herbaceous plants do not have that advantage. They start from the soil line in spring and die back to the ground in fall. That means they have to expend a tremendous amount of energy during the growing season to produce all those stems and leaves and to help them out, we need to make sure they have the fertilizer they need.

Is there a difference between the fertilizer needs of annuals and perennials? Annuals complete their life cycle in one growing season, so they do need more fertilizer than perennials that have the advantage of starting over each season from a hardy root system. Of course, annuals could live with the same amount of fertilizer as perennials or any other plants, but to get the most out of them, it pays to provide annuals with fertilizer regularly throughout the season.

Do all annuals need the same fertilizer? Most annuals are grown for their prolific flowering but there are also some varieties grown for their beautiful foliage. Annual plants that are grown for their flowers need lots of phosphorus. That is the middle number in the analysis (10-20-10). Phosphorus encourages blooming as well as strong roots and disease resistance. Annuals grown for their foliage need less phosphorus and more nitrogen. Nitrogen is the first number in the analysis (10-20-10) and it encourages lots of leaf growth.

Is the same thing true with perennials? Yes. And since most perennials only bloom for a short period each season, it is even more important than with annuals that they have healthy, attractive foliage.

Can I use a product such as Miracle-Gro? Water-soluble fertilizer such as Miracle-Gro or Excel Gro™ are good for annuals. A really great product for promoting blooms on annuals is Bachman's Mighty Bloom™. Water-soluble fertilizers are easy to use for the plants, but they are also used up quickly. Be sure to apply water-soluble fertilizers regularly (every 2-3 weeks throughout the growing season for annuals). Water-soluble fertilizers can be used as an occasional quick snack for perennials, but shouldn't be the primary fertilizer. Perennials prefer a dry fertilizer that is more slowly released such as 10-10-10.

What about slow-release fertilizers? Products such as Osmocote that are applied early in the season and release their nutrients slowly for the next few months are good for annuals, but not for perennials. If you are using them on annuals, you may still want to give an occasional boost with a water soluble.

Is there a good organic alternative? Both Sustane and Milorganite are balanced organic fertilizers that will work with annuals and perennials. Keep in mind that organic fertilizer is much slower to release and plants might not produce quite as much growth or flowers. With annuals, organic fertilizers should be applied three or four times each season. A successful combination is to use an organic for the primary fertilizer and give the plants an occasional quick boost with a water-soluble such as Excel Gro™ or Miracle-Gro. With perennials, organic fertilizers should be applied in early spring and again in mid-summer.

Are there any annuals or perennials that are especially heavy feeders? Yes. There are a few annuals such as geraniums and impatiens that like to be fed faithfully. And the new "wave" petunias need to be fed weekly to do their best! Perennials aren't as demanding.

How will I know if the plants are getting enough fertilizer or the right fertilizer? If your plants aren't growing or blooming as much as you think they should, they may need a boost of fertilizer. With some plants, the leaves will be a lighter green than normal if they need fertilizer. But several other factors can influence plant growth or color, so it is a good idea to bring a sample in and ask a horticulturist before assuming fertilizer is the answer.

Is there a danger of over-fertilizing? Too much at one time can be hard on any plant, especially if the plant was even a little bit dry. Follow the directions on the package for application rates and you shouldn't have a problem. With all plants, fertilizing too often may result in excessive growth that is weak and susceptible to problems. Over-fertilized plants are more easily stressed by lack of water, excess water, insects or diseases. For perennials, too much fertilizing may weaken their root system and make them less winter-hardy.

Are there any other tips for fertilizing annuals and perennials? Water plants the day before you plan to fertilize. Carefully follow all the directions on the package and try to spread the fertilizer evenly. It's always a good idea to water dry fertilizers after they are applied. This helps activate them right away and keeps them in place. Keep in mind that fertilizers will leach more quickly through sandy soils than through heavy, clay soils.