Answer: Your lemon should be transplanted into another container of a similar or slightly larger size. Whiskey barrels do rot away over time, so you may want to change to another type of container. Large containers of terra cotta, styrofoam (painted and textured to look like clay), and plastic are also available. Just make sure and choose one with drainage holes. Placing the new container on casters to make moving easier is also a good idea.
When transplanting try to not disturb the roots any more than you have to. This will require a couple of helpers and even then will be a challenging task. Set the plant in its new container at the same depth it grew previously. Use a well drained potting mix. The soilless mix can be a bit chunkier than you use for other houseplants in smaller containers. Firm the mix in around the roots to remove air pockets and then water it in well.
Place the plant in as much sunlight as you can give it. Indoors will likely be too dark, so the deck is the better choice. The clear plastic cover can provide some protection from the cold as long as you have a source of supplemental heat beneath the cover.
Fertilize the plant with a slow release product like Osmocote or a liquid product such as Miracle Gro at the label rate. Most feeding should be done in the warm growing season. In winter the plant will need very little added nutrients.
Good luck with your new lemon tree!
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