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Monday, January 9, 2012

Why Is My Pine Tree So Sparse?

Q. Why does my one pine tree seem so sparse and inadequate?  I purchased four Mondale pines and treat them all equally. But the one shown in the left picture looks so scrawny.  The other one shown looks healthy and appears to be robust.  Any thoughts on that? 

Aleppo pine blight
A. The usual reason for a pine tree being sparse and not full is that it is not receiving the same treatment as the others. I have to assume the picture you are painting for me with words is the same one that I am seeing and understanding.
            When you say the tree is ”sparse or inadequate” this, to me, means that there are far fewer needles along the branches of this tree compared to the branches of other trees. Pine trees generally maintain needles on their branches until the wood gets to be three to five years old and then the needles are dropped from this older wood. This older wood is needle-less except for other small branches growing from it that are less than five years old.
            The reason for thinning is that there is not enough young growth covering the entire tree so that needles are lost at a higher rate than they are being replaced. If you were to look at the growth of the youngest branches you can actually see each year’s growth for several seasons and count back several years of growth on one branch. This gives you an idea of how much growth a tree is putting on each year so that it can be compared to the other trees.
            So bottom line for “thinning” is that the tree is not growing fast enough (or putting on enough new growth). I know that this seems a bit simplified but we have to start at the simplest point if we are going to try and figure it out. Reasons for thinning include water, fertilizer, damage to the tree, or disease or insects. So let’s follow the keep it simple rule first and handle the most frequent and common reasons. Once we have eliminated these then we can move on to the more “exotic” answers.
Pine tree dieback due to shading
            By far the most common reason is differences in the amount of applied water or water available to the plant. So when you say you treat them the same it does not necessarily mean these treatments are all reaching the trees equally. But if there is inadequate water two things will happen; the tree will put on less growth and the needles will be partially brown from the tips.
            The first thing to do is to check and make sure that whatever is delivering water to the tree is not plugged. Secondly make sure that water applied to the base of the tree is not running off the surface to some other location. Just because water is applied to a tree does not mean it is getting to the roots.
            Remember that as these trees get bigger their demand for water increases. The increase is not a simple few gallons per year but rather the increase is much more dramatic because trees are three dimensional in their water use unlike a lawn. A lawn doubles in size then its water use doubles. When a tree doubles in size its need for water is probably more than double.

Pine tree thinning due to lack of water
            One tree showing signs of water stress might be an indicator that in the next few years the others may also show the same signs. What you are seeing is a snapshot in time and may not indicate what will happen in future years if all things remain the same. As a precaution, I would start to increase your water to the trees and supplement the thin tree with some water from a hose to see if there is a difference.
            The next most common reason is that the roots of the tree in the container never fully established into the surrounding soil after planting. This can be because the tree was too old for the container and the roots started circling inside the container.
            It can also be because the tree was not firmly staked at the time of planting so the root system doesn’t move. You should be able to push on the trunk and NOT see any movement of soil at the base of the trunk.

Mondale pine dieback due to unknown,
nonpathological problem
            If you see movement of soil then the tree most likely never successfully transplanted from the container into the hole. If the tree moves easily in the soil then it is difficult for them to ever get established and most likely never will if it has been five years and they haven’t.
            Trees need to be firmly staked when planted to immobilize their roots and give them a chance to get established in the amended soil surrounding the container roots. If this is the case you are better off getting rid of it and replanting.
            A third possibility can be that it was planted too deep. If planted too deep the tree can die fairly quickly in one season or linger for several years due to damage to the trunk from disease organisms.
            Pull the soil away from the trunk and see how deep the first roots are. They should be no more than perhaps half an inch from the soil surface. Sometimes soil can fall back into the hole after planting, the plant can sink in the hole (this is why I tell people not to dig the hole deep but rather wide) or mulch can be pushed up against the trunk when it is young causing a disease called “collar rot” to develop.

Pine tree damage due to weed killer ie
herbicide (dicamba)
            The next most common reason is damage to the roots or trunk. This will be far less likely than a watering problem but much easier to identify. This can be physical damage like construction, damage from chemicals like salts or weed killers, insect or diseases like collar rot.
            If it is insects or diseases it is most likely to affect a few branches rather than the entire tree unless the damage from insects or diseases occurred to the roots or trunk. If damage is to the roots or trunk then thinning may also occur and look very similar to a lack of water.
            So inspect the trunk for loose or damaged bark. This can include damage from equipment like mowers or line trimmers if it is in a lawn area or surrounded by other plants. Check and make sure the tree is firmly anchored in the soil after this number of years.

            If none of this seems to pan out lets follow the keep it simple rule for now and increase your water during the spring and summer months.
            After looking at your pictures again another reason occurred to me. That is shade. If the tree is being shaded by other plants and not receiving enough light (at least six hours a day) then these branches in the shade can drop their needles. If this is the case then some pruning to allow more light will help.

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