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As you take a summer drive through the city and look around it seems that there are more than usual the number of trees that have blown over. Is the weather changing, or what?
Here are some thoughts on why this has happened. First, we seem to be having more gusty winds–microbursts some people call them, and they seem to be more locally concentrated than before.
Secondly we know that people plant faulty trees from the nursery whose roots are going round and round in the container. Take a look at the picture on page 47 of my book “Desert Landscaping” to see the roots of a tree that will surely blow over, no matter how much care you give it.
Thirdly,we know that older established trees whose roots spread into the neighbors’ yards are not getting the irrigation they used to get when every house had its grass lawn. Turning grass into gravel certainly saves on the water bills but it denies the neighbors’ trees the water they used to get.
Even newly planted trees, especially if they are desert adapted, may not be getting the establishment care (that includes watering) in the mistaken belief that they are maintenance-free. And they may not have been planted properly in the first place.
Poor branch managment often creates too heavy a top growth of foliage, and this means the wind buffets against the tree when proper thinning allows the wind to blow through. People forget that cutting back is a sure way to get new branches which makes a tree top-heavy. On the other hand, removing congested branches at their origin (against the limb or trunk) actually thins the foliage and allows the wind to pass through.
Many of the urban trees that have blown over show their roots have not gone deeply into the soil. In the natural desert, where trees have grown from seed we find that roots have found their way through cracks in the soil. Where they could not do this the seedlings died as soon as the rains stopped. Roots grow where the moisture is; they don’t go “looking” for it. In the urban setting our trees’ roots stay near the surface if the irrigations are shallow, or where the soil has not been disturbed by a good planting hole. Remember that, in a natural situation our rains are short lived and the summer rainstorms run-off instead of soaking in. As tree-minders we have the change all that by long slow irrigations that go deeply—and the roots will follow.
Further, if we plant in hard compacted soil there’s every reason to break up that hard soil down as deep as we can go. If there’s super-hard soil containing caliche there’s an additional reason to go even deeper. People who have dug a planting hole five feet down and five feet square ensure that they will have a tree with strong deep roots and it will not blow over.
As you return the soil into your deep hole, stomp things down. Such a light mix (that you have made simply by digging it out) is bound to settle and sink so you don’t want it to drag your new tree with it. In the process of filling the hole you can widen the top eighteen inches by using that as back-fill. It will be a better soil than the stuff that came out of the bottom of the hole and never saw the light of day or rain that encouraged organic growth. At the same time you’ll be widening an area of disturbed soil for the sake of surface roots.
For two years water deeply (down to three feet) in order to get deep roots.
Support the newly-planted tree with a stake that is lightly tied to the trunk. The picture of such a tree on page 204 of my book “Desert Gardening–Fruits and Vegetables” shows how to use a figure of eight soft cotton rope tie that allows a trunk to flex in the wind and grow with strength.
Lastly, don’t “head back” any new growth, because it will simply thicken the foliage and this gives the wind enough resistance to blow the tree over. Instead, thin the branches to allow the wind to blow through them. Some people say provide enough air space to let the birds fly through safely.