Answer: Based on your description I am not certain what happened to your trees. Probably the most common reason for loss is that they are either underwatered or overwatered. When you have a newly planted tree, the soil needs to be kept evenly moist like a wrung out sponge. It should not be sopping wet/saturated nor bone dry. If the trees were well watered at planting time and then mulched, watering would not be needed so often as every three days. There is no set schedule for watering. Instead, you would dig down and feel the soil with your finger and water when it began to feel dry. Watering should be done slowly and thoroughly so it can soak down into the soil and encourage deep rooting. (It is better to provide a deep soaking less often than to water lightly at short intervals.) After watering, wait a few hours and then dig down to see how far the water actually went. Sometimes it can be surprising.
There are many reasons a new tree might fail to thrive, however, including poor planting technique or planting a tree that is poorly suited to the growing conditions where it is placed. Another possible cause is a pest or disease problem, or even overfertilizing which can burn tender new roots.
I would suggest you consult with the retailer where you purchased the tree and also the installer, to see if the trees are truly dead, if there is any warranty that might apply, and to determine more precisely what happened to them.
I'm sorry you are having trouble with your trees.
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