The average height of the willow trees in your area depends largely on which varieties are growing. There are four main types that grow in the U.S.: weeping willow, desert willow, pussy willow and curly willow.
Based on plant profiles published by the National Arbor Day Foundation, the average height of a willow ranges from 15 to 40 feet high. The desert willow and pussy willow both reach a mature height of between 15 and 25 feet. The curly willow averages a height of 30 feet, while the weeping willow grows to between 30 and 40 feet tall.
As the height varies depending on the type of willow grown, so does the spread or average width of the tree. Desert willows reach an average spread of 10 feet, according to the National Arbor Day Foundation. The pussy willow averages between 12 and 25 feet, and the curly willow averages between 15 and 20 feet. The weeping willow is the largest tree, with an average spread of 35 feet.
The best way to ensure that willow trees reach their ideal height and spread is to plant species in their ideal climate. The weeping willow and curly willow grow best in the moderate climates of the mid-United States, or in U.S. Department of Agriculture planting zones 6 through 8. The pussy willow thrives in zones 4 through 8, and the desert willow is ideal for zones 7 through 9.