A 2 to 4 inch layer of some organic material such as chopped leaves, wood chips or shredded bark will keep the soil under the tree moist, and discourage weed problems.
Willows require lots of water. They like their soil to be moist, preferably wet, all of the time. Be sure to plant them near a source of water like a pond or creek. They will need supplemental water when they are first planted and just before the winter freeze. During periods of drought when rainfall is scarce and creeks dry up, they will need watering once or twice a week.
Because they grow so rapidly Willows are heavy feeders, and extra fertilizer may be needed to keep them flourishing. . If you live in a region with a short growing season, apply fertilizer only in the spring, because if willows grow too late in the summer their new growth will not harden completely before frost, resulting in winter injury. Otherwise in both spring and fall sprinkle a granular all-purpose fertilizer on the soil under the tree out to 1-1/2 time the distance from the trunk to the tips of its branches (the drip line). Do not let the fertilizer touch the trunk. Use about 1/2 pound of fertilizer for every 1/2 inch of trunk diameter measured at its base. For larger trees, use one pound for each inch of trunk diameter. Do not apply fertilizer when planting a tree, nor during the first season.
Willows do not normally need pruning. However, winter storm damage to brittle limbs may require some trimming. Remove all broken or splintered branches.