It may be time to re-pot this lime tree.

One of the most often-asked questions I receive about potted gardens is: How often do I need to change the soil in my pots?

As is the case with many questions concerning potted gardens, there is no simple answer. If you find these instructions confusing, please do not hesitate to email me with your specific question.

• Note that potting soil is a “soilless” mix. Be sure to select a quality product, one that is rich, deep brown and smells earthy. Always add new fertilizer (organic and/or time-release) each time you newly plant a pot.

• For pots 24 inches in diameter and less (ones that you can somewhat easily move): You will want to replace the soil in the following situations:

  1. The pot is root bound with its plants.
  2. The plants that were in the pot died due to disease or pests (in which case you need to sterilize the pot before reusing).
  3. The soil no longer holds water.
  4. There is a lack of richness or “earthiness” in the soil.

• For pots larger than 24 inches in diameter: They are very cumbersome to change out entirely, especially with a large plant—and “really big pots,” which are 32 inches in diameter and larger, are VERY difficult. Still, there are certain circumstances in which I would suggest that you do get some strong bodies to help and get the plant taken out, with the soil changed.

Even in large pots, plants can become root-bound. The choice is to either take the plant out and give it a permanent place in your landscape, or to trim the roots. In the former, be sure to plant it during the appropriate season to plant’s needs and tolerance.

If the plant can tolerate a root-pruning, you can remove it from the pot by laying the pot down on its side (this is where the muscle is needed) and gently extracting it. Then you can reduce the root volume by up to one-third and repot the plant—with all-new potting soil. Citrus trees and many shrubs such as the myrtle family of boxwoods respond very well to root-trimming. Palms do not do well with root pruning, in my experience.

Be sure to water the plant very thoroughly after repotting.

If the plant is not root-bound, and the soil level has dropped from its original height, you can add new soil once a year. I suggest you follow these steps:

  1. Remove a top layer of old soil without “assaulting” the roots. They will be OK if you move or tear some, so you do not need to be meticulous—just mindful.
  2. Add new soil to replace the amount you took out, mixing it into the lower level of soil if possible.
  3. Add organic and/or time-release fertilizer, and mix it into the top 6 inches of soil.
  4. Bring the soil level up to the original level on the trunk of the plant.
  5. If the plant and soil have sunk into the pot lower than the desired height, and you do not want to remove the plant to lift it, you can increase the level of soil by up to an inch per year without suffocating the plant.

If you only have 20 minutes in your desert potted garden this week: Deadhead your potted flowers thoroughly, trimming back to new growth. Extend the life of your summer flowers a couple of weeks!

Marylee is the founder and former owner of The Contained Gardener in Tucson, Ariz. She has become known as the Desert’s Potted Garden Expert. E-mail her with comments and questions at potteddesert@gmail.com, and follow The Potted Desert on Facebook.