Answer: Actually, many desert trees grow naturally with multiple trunks, such as palo verde, mesquite and desert willow. All those low--to-the-ground branches provide cover for other plants and creatures, and also prevent strong thunderstorm winds from getting beneath the canopy and "lifting" the tree out of the ground, since roots are somewhat shallow. Regarding citrus, most have typically been pruned as one trunk in landscape situations, however, that isn't essential. It is better to allow all of those lower branches to remain and shield the trunk from sunburn. That is why you see most citrus painted white, to protect the bark, but the branches do just as good a job, and it takes less work. It also makes it much easier to harvest fruit when the branches are low. That is how they grow in orchard production. Finally, just recently, I was in a homeowner's yard with a lemon tree with multiple trunks that was not painted white. It blended into the rest of the plantings beautifully (that white paint is rather garish) and was a very attractive tree. So, it's up to your personal preference.
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