GARDENING: Time is running out for pruning trees this season

Lots of questions are surfacing on pruning. A couple that came to the Master Gardener Orchard said they had been reading this column, but, after seeing my demonstration, noted they had been doing it wrong. I had mentioned to remove one-third of a plant's canopy so they were removing one third of each branch and doing this to fruit trees. No, no, no. This can be the trouble when pruning using an instruction manual.

There is not much time left for pruning. The orchard is open for fruit tree pruning demonstrations on Saturday from 9 to 11 a.m.

The one-third rule only applies to ornamentals and usually to renewing older shrubs. It never talks about removing one-third of all branches. The one-third rule does not apply to fruit trees.

On shrubs, renewal pruning of older shrubs is done by reducing the volume of the canopy by cutting way into the interior of the plant. Let me explain.

When pruning older shrubs, you want to renew the shrub, or drop the size a bit -- reduce the canopy volume -- and get some new interior growth to replace older growth (renewing). A shrub that needs renewing is one that shows a lot of wood and is no longer dense and leafy. Renewal pruning causes the shrub to become denser from top to bottom and, if it flowers, increases the flowering.

Let me group shrubs into three categories based upon how they grow. Generally speaking, shrubs may grow from one central trunk, arising from the ground; several smaller trunks, growing collectively from the ground; or arise from many small trunks, growing from ground.

The easiest shrubs to prune are the shrubs with lots of small trunks arising from the ground. An example might be heavenly bamboo. Sometimes oleanders can be found growing like this as well. All you have to do is remove one-fourth to one-third of the largest trunks, which are also the oldest and usually the tallest, level with the ground.

Frequently these are located toward the center, which can make them hard to remove. Pruning out the older wood gives the remaining trunks space to grow, more sunlight, and causes many more trunks to arise (renew) from the ground.

The second easiest to prune is when the shrub has one central trunk arising from the ground. In this case, remove branches from the central trunk at the point of attachment. Removing one-fourth to one-third of this wood will cause new branches to arise from the central trunk and renew the canopy.

The last category is when you have a few trunks arising from the ground. This is more difficult because by removing an entire trunk from the ground, you may remove too much of the canopy. In this case you may have to use a combination of the two previous techniques above.

Remember that opening a plant to sunlight will stimulate new growth where the sun lands in the interior of the plant.

Question: I am getting ready to paint my trees. How far do I paint the trunk? Do I paint all trees or all fruit trees? I forgot the purpose of painting the trees.

Answer: The purpose of painting trees is to prevent sunburn of the exposed trunk and limbs after pruning. Sunburn damage attracts destructive insects like borers. The white paint, or whitewash, reflects sunlight and reduces heat and subsequent damage from intense sunlight.

If the tree has a full canopy, then painting is usually not necessary. But stone fruit, like peaches, nectarines and apricots, may be pruned heavily to improve fruit production. When pruned like this, it opens the canopy of the tree and puts the trunk and lower limbs in danger of being damaged by the sun and then borers attack the damaged areas.

Paint these tree trunks and lower limbs on the south and west sides and all of the upper surfaces of main limbs, up to about 3 to 4 feet above the ground. Paint all surfaces up to this height if you want it to look better. You would use a whitewash or a diluted white latex paint that will cover the plant surfaces easily and still reflect light. Try diluting it 50/50 with water. Actually any light-colored latex paint is fine.

Ornamentals can be painted like this as well, but it usually is not necessary and usually looks a bit odd on these types of trees.

Q: Are the dormant sprays applied to all fruit trees? Or all trees and plants?

A: We are not applying a dormant spray, but dormant oil as a dormant spray. The oil is used primarily for insect control. The insects controlled are primarily aphids, scale insects, mites, thrips and the like, not borers.

There are other dormant sprays that are used for disease control. These are frequently called dormant sprays as well. The dormant oils will not do much about disease control. You will apply a dormant spray for disease control only if you have had disease problems in previous years. Otherwise you will skip the dormant spray for disease control. We do not have that many diseases here in our dry, desert climate. You will get confused if you call it just a dormant spray.

The dormant oil applied as a dormant spray can be applied to any plant. Other plants can be sources of plant pests for your fruit trees particularly if they are ornamental forms of fruit trees like flowering plum or ornamental pear. Roses are notorious for supplying plant pests to fruit trees if they are not cared for. In fact any landscape plant in the rose family such as pyracantha, cotoneaster and others can be problems.

If it were me I would apply dormant oil to all my landscape trees and shrubs. The best time to apply it is as late as possible in the spring before new growth appears or just as new growth appears but avoiding anything in flower.

Q: I took an irrigation class at the garden last week. I noticed a sign posted in the classroom that topping hurts trees. So I am confused. Aren't you recommending to lower the height of fruit trees by topping? Which information is correct?

A: The purpose of pruning fruit trees is entirely different from ornamental trees and the two are usually not pruned the same way if you are only interested in fruit production.

The technique we use for lowering the height of fruit trees is not topping. The technique is called drop crotching. This is lowering the trees by cutting the taller branches at a crotch or where two limbs come together.

Sometimes people want both; a fruit tree that will actually produce fruit and look good as a landscape tree as well. Then we have to modify the pruning of the fruit tree with some techniques that we use on ornamental trees. This kind of modification may result in less fruit produced, poorer quality fruit and more work in caring for the fruit tree. These are tradeoffs we must consider when we decide how we will prune fruit trees for our own personal landscape. The orchard is only looking at production of fruit, not necessarily beauty. One of the objectives we set for ourselves at the orchard is to pick fruit from the ground and not use ladders. For this reason we do a lot of lowering the height of our fruit trees. Sometimes this may result in trees, after pruning, that aren't the prettiest to look at but look fine once the leaves come out.

But when we prune heavily, like we do at the orchard, it is imperative that we protect the tree from sun damage because it is so open. The trees in the orchard that are the most subject to borer damage are the peaches, nectarines, apricots and plums. Apples and pears are usually not as prone to borer attacks unless they are heavily pruned.

Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.