With the warmer weather starting to return, we pay more attention to our landscapes. Spring is an excellent time to give our plants a boost of energy through fertilization.

But first, remember that not every landscape plant needs fertilizer. There is no sense feeding plants that are overgrown and becoming constant maintenance problems.

Mature shrubs can go years without fertilizer. And many times it's best not to keep pushing more growth. Likewise, there is often no need to fertilize mature trees separately if you're already fertilizing your lawn.

Many plants, though, need fertilizer, such as young shrubs, roses and certain annuals and perennials. For those, late March to early April is a good time to start.

Research shows that woody plants actively absorb nutrients from the soil during the growing season. But they need few nutrients during the winter. So fertilize as soon as the plants begin breaking dormancy in the spring. And don't apply it after the first fall frost.

The best way to tell your plants' nutrient needs is to take a soil sample to your county agent. (Check in the phone book under "County Government.") This test will show how acid or alkaline your soil is (the pH) and whether you need to add lime.

If you don't have a soil test, most landscape plants will benefit from a fertilizer having all three primary nutrients: nitrogen (N), phosphorus (P) and potassium (K).

Be careful not to overfertilize. You may injure your plants.