According to Four Winds Growers, container citrus trees need to be repotted every 12 to 16 months, when they outgrow their current container. If your lemon tree seems to be in decline or has less growth or yellowed growth, it's time to transplant the tree. Once repotted, your lemon tree should resume its healthy growth. Replant your tree at any time of year, working outside if possible so you'll be able to clean up spilled soil easier.
Select a container with smooth, straight sides that's one size larger than the container currently holding your container citrus tree. The container should have drainage holes so your tree doesn't develop root rot.
Cover the bottom of the container with a mesh screen, which will prevent soil from washing out the drainage holes.
Fill your container 1/3- to 1/2-full with potting soil. Use a potting soil mix that works well for lemon trees.
Grasp the trunk of your tree and pull it out of its container. Four Winds Growers notes that this is easier if you've allowed the soil in your container to dry out for two or three days. Pull the tree free of its container.
Massage the root ball between your hands to break it apart before replanting your tree; crumple any soil clusters between your hands. Untangle tangled roots. Clip the ends of any broken or damaged roots using your pruners. When all of the roots are free of soil, unwound and trimmed it's time to plant the tree.
Place your lemon tree in its container so it sits at the same depth it was planted before. Spread the roots out in the soil with your fingers. Check to make sure the tree is straight before completing the planting.
Top off the container with potting soil within 1 inch of the lip of the container. Press the soil around the tree trunk gently, without using too much pressure.
Water the newly repotted tree until the soil compresses around the trunk of the tree. Add water until you see water flow out of the drainage holes at the bottom of your container.