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 in the case of many questions concerning potted gardens, it is not a simple answer. As I write this and see the length of these instructions, please do not hesitate to simply email me with your specific question.
(Note: potting soil is a ‘soilless’ mix. Be sure to select a quality product that is rich, deep brown and smells earthy.)
24” diameter and less pots — 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’ characteristic of new potting soil.
*Always add new fertilizer (organic and/or time release) each time you newly plant a pot.
However, pots that are larger than 24” are very cumbersome to change out entirely, especially if planted with a large plant. As I continue to talk about ‘really big pots’ that are 32” in diameter and larger, the difficulty intensifies. There are certain circumstances where I would suggest that you do get some strong bodies to help and the plant is taken out and soil changed.
Even in large pots, plants can become root bound. The choice then is to either take the plant out and give it a permanent place in your landscape by planting it in the ground or to trim the roots. In the former, be sure to plant it during the appropriate season for your specific climate and the plant’s needs and tolerance.
The other option is 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 from the pot. Then you can reduce the root volume by up to one third and repot the plant into the same pot 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 very well with root pruning in my experience. Be sure to water the plant very thoroughly after repotting.
Finally, 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 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 ½ to 1” a year without suffocating the plant.
6. And, as always, water in well.
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Marylee is the founder and former owner of Tucson’s The Contained Gardener. With more than 15 years of successfully designing and growing potted gardens in the desert’s challenging and oftentimes harsh climate, Marylee has become known as the Desert’s Potted Garden Expert. Marylee is available for local and digital consultations and you can always email her with your questions and comments. Follow The Potted Desert on Facebook!