In this episode of Desert Horticulture learn that visual and nonvisual types of damage that occur to landscape plants, (vegetables, fruit and ornamentals) and how to control it.
Controlling the Wind Is an Important Part of Desert Horticulture Read More »
Windy Weather Windy weather, like we had over a past weekend, is very damaging to plants. (Notice I said “is” and not “can be”?) Light winds cause very little damage. Moderate winds cause moderate amounts of damage. Strong winds cause lots of damage. Why? I can think of at least two reasons; extent of damage and water use. Shallow rooting of tree because of annual flowers planted at its base. Vegetables and Wind Vegetables grow the best when located closest to the downwind side of a windbreak. Plants don’t care if the windbreak is living or not, they just want the wind slowed. For this reason, the best windbreaks are not solid walls (e.g., block walls) but perforated walls (e.g., chain-link fence with slats inserted in them). Solid walls cause the wind to swirl. Perforated walls cause the wind to slow. Science has shown us the best windbreaks are about 80-90% solid, not 100% solid. Windbreaks for orchard in a canyon Wind Damage and Fruit Trees Examples of damage include leaf and flower damage with small fruit ripped from the tree with some types of fruit trees. Plants grown in windy spots are smaller than plants grown in protected areas. In strong windy locations I have seen fruit trees that lean away from the wind. Wind damage to fruit trees is the worst on trees closest to the wind. Wind damage lessens on the second and third row of fruit trees. Plant fruit trees in blocks so they give each other wind protection. Locate fruit trees that tolerate wind damage the most on the windward side of the block. Examples of wind tolerant fruit trees are pomegranates, apples, and pears. These trees will protect the less wind tolerant fruit trees. Fruit trees less tolerant of wind include citrus, plums, apricots, and peaches. Wind and Water Use Plants during windy weather use more water. If the winds are strong and continuous, they use more water! Wind is a strong predictor of plant water use. In fact, along with how bright the sun is shining it is one of the strongest predictors of plant water use. Pay Attention Go outside in the morning. Look at the weather. Is it bright and sunny with very few clouds in the sky? Winds is a major predictor of high-water use. Look at the trees. Are the leaves moving? Look at a flag flying on a flagpole. Is the flag barely moving? Is the flag flapping a lot? Is the flag rippling because of the wind? Those are indicators of wind strength. Bright, cloudless skies and strong winds equals high water use in our desert climate. It’s time to water during bright windy weather.
Wind is Damaging to Plants Read More »
Q. My African sumac tree has a fungus in it. I am thinking of cutting off the whole main branch because of the disease but it’s a guide branch and I hate to do that. Or can I just cut off the branch that broke? Any info you have would be greatly appreciated! Bottom picture is limb of African Sumac reportedly dead. The top picture is the inside of the limb cut open to show the dead part inside. A. The disease won’t spread to healthy parts of the plant. The rot or disease spreads internally inside the tree because it’s what we call “saprophytic” and only attacks dead or very weak wood. There is nothing you can do to stop it. Tree Biology The center of the tree is composed of dead wood. The only living part of the tree is a thin ring just under the bark. This living part is strong enough to stop the spread of this “saprophytic” disease. The only thing you can do to help your tree is to make sure that whatever you use to cut or prune the wood is as clean and sharp as possible. Narrow crotch angles are not good in landscape trees. They are shaped like the letter “V”. After time they start to split as their weight increases and rot can begin on the inside of the trunk. Narrow crotches start to split during the wind and its internal dead wood begins to rot. This rotting will not affect the living parts of the tree. Only the dead parts. My guess is that this “rot” started at the top of a narrow crotch; where two limbs come together. Narrow crotch is making the letter V when you look at it. Week crotches can split in strong winds particularly if the inside of the tree has been starting to rot there. A strong crotch angle makes the letter “U” and less likely to start rotting in that spot and then split apart in strong winds. Prune it enough to shape the tree the way you want it. Just cut off the branch that broke very close to the next larger branch and let it heal and completely close it off in three or four years. It takes longer to heal if it’s not cut close to the trunk so there is no longer a stub remaining. If the tree looks healthy to you otherwise then don’t worry about it. Cut off the limb close to the trunk with a clean blade.
African Sumac Limb Disease Read More »
I said it might happen and it did. http://xtremehorticulture.blogspot.com/2011/09/problem-with-pruning-pine-trees-so-they.html This pine tree has a limb that broke in a windstorm not too long ago. It is just at the bottom of the trunk. Thinning pine trees by removing smaller limbs from larger limbs (thinning the canopy) is NOT a good idea. This has been a relatively recent trend in tree trimming (I do not want to call this arboriculture) is done to reduce the potential that trees will blow over in high winds. Instead, thin the canopy by removing entire limbs from the trunk to reduce wind damage and blowover . Here is why. Plants grow both in length (called primary growth) and width or diameter (called secondary growth). When secondary growth occurs along a limb or trunk, progressively, as it get longer, then the limb or trunk exhibits “taper” or a gradual increase in girth along its length. This is good unless you are growing trees to use as telephone poles or for lumber. A plant develops taper along its trunk or large limbs if the trunk or limb can bend freely in the wind as it is growing. The free movement of the tree trunk or limbs increases the degree of taper. If the trunk or limb is held so that it cannot move (staking so no movement occurs), primary growth increases but its growth in girth (consequently its degree of taper) decreases. Here is the limb that broke Taper also inceases if smaller, lower limbs are left attached to a limb or trunk. These smaller limbs, with leaves attached, send carbohydrates manufactured in the leaves or needles back to the limb or trunk. This helps “feed” secondary growth causing more taper at areas closest to those small limbs. A distribution of smaller limbs along a trunk or limb causes an increase in its degree of taper. On the other side, removing these smaller limbs along a trunk or limb REDUCES the degree of taper. The limb that broke is in the center of the picture. Notice how little taper the limbs have. Leaving all the growth at the ends of the branches also causes the limbs to have a “weeping” effect. When a trunk or limb bends, and it is tapered, the stress of the bend (shear) is distributed along a great deal of its length. If there is little taper to a limb or trunk, then the stress is localized at a very small portion of its length. When a limb is not tapered, the stress of bending causes the limb or trunk to “snap” (shear) at its weakest part or where the majority of the “load” or stress is localized. Here are three principles to follow to increase taper in a tree: 1. When planting a tree, make sure stakes are located as low on the trunk as possible. Tree stakes should keep the rootball or rootsystem stabilized, not the entire trunk. The trunk and limbs should be free to move in the wind if possible. 2. Remove stakes as soon as possible after the root system has become established. This should normally be one season or less. If it is longer than this then you may have a problem. 3. Leave smaller limbs attached to the trunk for three to five years if they are healthy and vigorous. Try to maintain a ratio of canopy length to pruned trunk of at least 2:1.
The Problem I Warned About on Pruning Pine Trees Just Happened Read More »
A fairly recent trend in pruning in Las Vegas has been pruning pine trees so they don’t blow over. We have some wind gusts that periodically get pretty nasty when they reach speeds of up around 70 mph (112 kph) or more. The trend was to remove some of the canopy so that there is not so much leverage on the root systems. This leverage, or sail effect, by the wind can pop the trees over when gusts come up quickly and our trees can be pretty shallow rooted which does not help to anchor them. This Mondale pine was pruned probably in an attempt o reduce with wind load (sail effect) on its canopyand help reduce the potential for blowing over You can see that removing the inner small branches concentrates the weight of the new growth all on the ends of the branches causing them to bend and in some cases to break I have some concerns about thinning pine trees to allow more wind to blow through their canopies. Not that it is done but really more about HOW it is done. Take a look at this picture of a pruned pine tree just for that purpose. Most pine trees will not regenerate new growth on older branches once this growth is removed. Once the wood is older than about three years old most pines will not cause new growth to come from this older wood. Once this young wood is totally removed, it is gone for good. By removing these small limbs in the interior it prevents pines like Mondale from renewing the removed growth. The juvenile part of the limb is now concentrated only in the growing tips which are all at the ends of the branches. This might be good in theory (the tree trimmers don’t have to come back as often). But this can create a problem.Think of a fishing pole. Why is the pole diameter tapered and not all the same diameter along its length? Poles or branches which are tapered help spread the stresses of bending along its length. If a pole or branch has no taper, then the stress of bending is concentrated in a very small area of the pole or branch which will increase its chances of snapping or breaking. By removing this small wood deep on the inside it also causes these “thinned” older limbs to no longer increase in girth (caliper or diameter).They bend more and more as the weight of the new growth is added to the ends of the branches. Pine tree with a canopy thinned a bit better so that limbs are less likely to bend and split A better approach would be to selectively leave some juvenile wood on the interior of these larger diameter branches so that these branches will increase in caliper and taper. So instead of removing ALL the small juvenile from branches deep in the inside, remove some but leave some as well. This still results in thinning and allows for wind to move throught the canopy easier and also results in distributing this increased load along the branches rather than concentrating the load in a small area of the branch which increases its likelihood of failure (snapping or bending). Just a thought.
The Problem With Pruning Pine Trees So They Don’t Blow Over Read More »