Answer: Willows will grow best if they receive ample water. Usually the amount of water the tree receives is the limiting factor, although fertility could also contribute. It is possible your neighbor's tree is in a spot that is naturally moister, such as a slight depression or at the bottom of a slope.
Or perhaps it is planted in a lawn area that is heavily fertilized and benefits from that. Also, there are different types of willows.
It may be that you have different kinds.
It is also possible that yours has not rooted as well as the other. The roots must extend out from the original planting hole or it will be stunted as though growing in a container forever. Eventually this strangles the tree. If the tree was rootbound at planting, the roots wil continue in that tight pattern. Sometimes with clay soil the prepared hole acts like a container. This is especially common when the sides of the hole are smooth and/or the soil in the hole is heavily amended so it is very different from the native clay.
You might dig down carefully and see, if the roots are growing in a circle inside the hole then you should reset the tree. Do not do it now, it is too hot and stressful. Do it in the fall. If you reset it, keep in mind the hole should be very wide and not all that deep. Loosen the soil thoroughly to encourage rooting, amend with a bit of compost if you feel you must, and replant. (Modern practice no longer includes adding lots of amendments, the tree should be able to grow in the soil you have.) If the roots are currently growing in a circle, you need to cut or untangle them when you reset it.
Watering is the most important thing to do for a new tree. Keep the soil evenly moist but not sopping wet. Water very slowly but thoroughly and deeply to encourage deep rooting. After watering wait a few hours overnight and then dig down to see how far the water went, it can be surprising. Clay soil holds moisture for a long time but is difficult to re-moisten once it is dry, so always check before watering. To know if you need ot water, dig into the soil with your finger. If it is still wet, do not water yet. Using a layer of organic mulch several inches deep will help keep the soil moister longer.
The tulip poplar is not going to branch from the lower trunk, no. It can only branch off of the existing branches where it is actively growing. Planted out in the open, it should begin to develop a wider crown and grow more symmetrically. However the initial framework of branches will not change. Keep in mind however that this tree is normally very upright. It also self prunes over time, losing its lower branches. Without seeing the tree it is difficult to say whether some corrective pruning could help, or not. You could consult on site with a professionally trained and certified arborist, they should be able to help you with the willow as well. This might be a good investment since the trees are likely to live for decades.
I hope this helps.
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