The main purpose of pruning roses is to remove all dead and diseased wood, and the best time to do it in the Washington area is late March or early April, earlier as you go south, later in the north.

The least desirable of two branches that rub against each other should be removed. They scratch each other with their thorns when the wind blows them, and they become more susceptible to disease organisms. Small twigs on the upper part of the plant should be cut off.

Some gardeners cut their roses back to about 12 inches to get larger blooms on longer stems. But usually it also results in fewer flowers, later blooming and shortened life for the rosebush.

Roses left at three to four feet or more will bloom earlier in the season and bear more flowers. Use sharp tools to prune: Dull tools are likely to crush the stems and the wound will heal slowly if at all. When a cane or branch is shortened, the cut should be made about 1/8th of an inch beyond a bud (node). If made at a greater distance, a stub is left which will die back.

The bud to which the cane is cut back normally will make the most growth in length.An upright bush can be made to spread more by cutting back to outside buds, and a spreading bush becomes more upright if cuts are made to inside buds (buds facing the inside of the plant).

Almost all modern roses are propagated by budding: A bud of the desired variety is inserted under the bark of the stem close to the root of a vigorous wild rose known as Rose multiflora. This method produces strong plants with unusually vigorous root systems.

Sometimes shoots will grow from the wild root system. This is called suckering. Years ago it was serious, but today suckering is rare because of the types of understocks used and their more careful treatment. But sometimes suckers do appear and they should be removed immediately after they are discovered.

Take some earth from around the base of the rose bush so you can trace the sucker to where it originates. Then by pressing down on the shoot, tear it out of the root itself. If you cannot tear it out, use a sharp knife and gouge it out. This is essential because any portion of the sucker that is left will send up more sucker shoots. Tree roses are budded three feet above ground on the stem of the understock. Suckers are much more common from both the roots and stems, and should be removed promptly.

Grandiflora and floribunda roses are pruned about the same as hybrid teas. Thin out the tops of tree roses and sherten the stems that are left. This keeps them from becoming top heavy. Minature roses should have long shoots shortened. Thin out the tops and cut them back somewhat to encourage new growth.

Q -- I have two philodendrons both six to seven years old and 10 to 12 feet high. My problem is they grow ugly air-roots or streamers. Can I cut these things off without hurting the plants? And can I cut the plants back a little and root whatever I cut off?

A -- The air roots can be removed without harm to the plant. For best results, take cuttings (cutting the plant back) in the spring when growth is in progress because they are much more likely to root. If you take the cuttings now or in summer or fall, they may root but it will take much longer. Use new green growth three to five inches long for cuttings. Remove the leaves from the lower two inches of the cuttings. They need rather high humidity to root well, and this can be taken care of by enclosing them in plastic bags. Keep them in good light but no sunlight for several weeks, then check them to see if they have rooted.

Q -- Is it better to purchase fruit trees from a local garden center or order them from out-of-state nurseries?

A -- Ask your garden center about the source of their fruit trees. If the source seems reliable, there are advantages to purchasing the trees locally. You can also plant them when the spirit moves you. On the other hand the local trees may have been picked over, the tags may be torn off or exchanged, and the salesperson may not be familiar with the stock.

Q -- Some wood smells better than others when burned in a fireplace. Which wood is generally regarded as smelling the best?

A -- Wood from a fruit or nut tree -- cherry, apple, hickory, pecan -- provides a pleasant aroma when burned.

Q -- I was given a beautiful gloxinia in full bloom. For about two weeks now the plant has not looked well, leaves turning yellow with browning edges. Can you please help me? I'm 82 years old and live in a place for the elderly, and I miss a garden.

A -- A dozen different things could cause the leaves to turn yellow. The main one usually is overwatering or poor drainage, which prevent oxygen from reaching the roots. Insufficient light also could be responsible. Browning of leaf tips could be due to dry air, or plant too close to the radiator, or root-rot from overwatering.

The plant needs very good light, but keep it out of direct sun. Water with room-temperature water, until it leaks from the drainage holes at the bottom. Wait 15 minutes for excess water to drain, and then empty the saucer. Usually, watering every four to six days is sufficient.

Q -- Can azaleas be dug up and divided into several plants?

A -- No. You can get new plants by taking cuttings in early summer and rooting them, and you can transplant them almost any time of the year when the weather is suitable. Don't attempt to divide them.

Q -- How often should the soil in a home garden be tested for lime need ?

A -- At least once every three years usually is sufficient.