Though, as the name implies, it is the Weeping Willow's nature to bend with its branches touching the ground instead of reaching for the sky, you can help your Weeping Willow add some height by staking the tree at the base while it is still forming. Once staked, the Weeping Willow has a stronger central trunk that can stand upright, but the top of the tree above the stake and the branches still bend naturally.
Hang a windsock in the area of your yard where the Weeping Willow is planted. Watch the windsock for a few days. You should see a trend as to which direction the wind blows. This is the prevailing wind in your area.
Hammer a wooden stake into the ground directly beside a newly planted Weeping Willow using a rubber mallet. The stake should be just shorter than the tree itself and located on the side of the tree that faces the prevailing winds.
Select a thick central branch of the Weeping Willow to serve as the main trunk of the tree. Gently hold it up to its full height against the stake.
Tie the central branch to the wood stake with tree ties. Use enough of the ties to make sure that the branch stays flush against the stake from top to bottom.
Leave the stake in place on the tree until the Weeping Willow has grown to the height that you want. When the tree grows taller and a trunk forms, you can wrap a tree guard around the base of the tree to protect it from damage.
Remove the tree guard, ties and stake when the tree has reached an acceptable height. The tree should continue to develop naturally.