To promote optimum flowering in shrubs, take out the branches that are older than 4 years old. Older branches are more susceptible to insects and disease than young, vigorous growth. Remove whole branches at ground level to open the interior of the plant - more air movement and sunlight can reach the inside and prevent disease.

You might wonder how to tell if branches are over 4 years old. If you have not been doing renewal pruning in the past, I could explain how to determine the age of a shrub branch; however, it is easier to just follow a simple pruning routine to make sure all your shrub stems are young.

The first step in renewal pruning is the removal of 20 percent to 30 percent of the largest stems at ground level. If you eliminate one-fourth of the stems each year, after four years all stems will be younger than 4 years old. If you continue to follow this practice, you will always have all the stems at their flowering peak, meaning the prettiest shrubs.

Cut as low as you can without damaging the stems you are going to leave. Every year, check the plant for the largest stems: If the plant has 10 stems, remove two or three; if it has 20, remove four to six. Do not leave any stumps above ground - any new growth coming off the sides of a stump will have a weak attachment point as the old stump rots away.

Next, remove dead branches or branches growing across the interior of the plant. Then cut back to an outward growing branch or bud, which includes any stems that are too long or growing out of place.

Shrubs usually have buds along the stem in matched pairs or alternately left and right along the stem. Opposite branching is found in dogwoods and viburnums, while alternate branching is found in most other shrub families.

When shaping the plant, remove the branches at points next to buds or side branches that face toward the outside of the plant. Do not just cut off a branch in the middle between buds, leaving a long dead stick. This dead stem section will not grow a new bud or branch; it will just die.

As new growth comes up from the root system, watch to see which stems should stay and those that need to be nipped in the bud. Keep stems that are farthest from the middle, so that the new plant will be more open and airy. Try not to save any stems that come off the old trunks. After the cuts have dried and healed, cover them with some mulch to slow the growth off new shoots on the stumps.

All of these plants will have grown next year's flower buds on the branches by the end of this summer. Pruning out old wood in the spring will permit new stems to grow this summer and set the flower buds.

If you have an old, mature or overgrown specimen of a spring blooming plant, it might have only a few large trunks. There are several options for old shrubs. They can still be pruned using this renewal method, taking out a third of the old plant each of three years in a row. An old plant that has a major trunk removed might look awkward the first year, but it can send up enough shoots to fill in and look even better the next year.

Often these mature plants are large enough that they can be the size of a small tree. The bottom side branches can be removed to finish creating the effect of a miniature tree.

Another pruning method that can be used is called rejuvenation pruning. It is a bit more risky and should be done just before new growth begins in the spring. You would cut the old trunks off about 1 foot from the ground; most old shrubs will send up a vigorous group of new stems from the roots. Remove all of the weak ones including those growing too close together. It is usually best to keep as many as a dozen widely spaced shoots to replace the old plant. The risk is that there will be no new growth and the plant will be killed by this method. So use it as a last resort.

Because you are going to do the pruning in the next month or so, go ahead and cut off a few branches while they are in bloom and bring them inside for the enjoyment of their beauty and fragrance.

By pruning spring-blooming shrubs in this manner, with only out-of-place branches pruned at other times, you will completely renew the plant every few years and always have the most possible flowers from your shrubs.

A couple of final notes:

- Never spray or paint anything on the shrub branch after it is pruned. It will heal faster if you don't.

- Use a sharp pruning tool for safety. Sterilize it with rubbing alcohol between cuts when cutting diseased stems.

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