Size

• The easiest trees to grow indoors are dwarf varieties. Meyer lemons (Citrus x Meyeri) are the smallest variety of lemon tree, and so fit inside the home most easily. Ponderosa lemons (Citrus limon 'Ponderosa') are also small trees, though slightly thornier. Small lemon trees handle living in the confined space of a large pot better than lemon trees that strive to grow larger.
  
  

Time Frame

• If you wish to merely overwinter your lemon tree indoors, you have a better chance of having a fruit-bearing lemon tree. Likewise, if you only wish to grow a lemon tree indoors for a few years, then you needn't worry about larger lemon tree varieties getting root-bound as they age. Any lemon tree can be potted, and fertilizing only sparingly will slow the growth rate inside the pot, thus delaying root cramp problems.
  
  

Type of Structure

• If you have a greenhouse, your options for lemon trees are even greater. True lemons grow to a height of 10 to 20 feet, but are often kept trimmed to 12 feet. So long as the roof of your greenhouse exceeds this height, you can grow any lemon tree in the ground in your greenhouse. For smaller greenhouses, size is again the limiting factor. Use dwarf varieties of lemon trees, since they grow to less than 6 to 10 feet tall.