Timing

• You can plant your oak tree at any point of the year; however, winter is an optimal time to allow your tree to focus on establishing its roots. A few weeks after planting you can give your oak tree seedling fertilizer to help the roots establish themselves in the soil.
  
  

Fertilizer

• Nitrogen is the main ingredient that oak trees need from their fertilizer. Dilute all-purpose fertilizer that has an NPK amount of 10-10-10 and apply the fertilizer a foot around the base of the oak tree.
  
  

Fertilizing Mature Oak Trees

• Fertilize your mature oak trees in the early spring. Use 10 to 20 lbs. of nitrogen per 1,000 square feet of area that accommodates your oak tree. Inject the fertilizer every 18 feet along the oak tree's dripline. The dripline is the area that is directly underneath the tree's outermost branches.