Repotting Indoor Plants - January 13, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Repotting indoor plants is fun and gives you an opportunity to inspect the root system and/or divide the plant to share with friends. Other reasons to repot include: outgrowing the pot; minimizing damage due to salt build-up; and, insect/disease problems. When repotting, you should consider potting media composition, size of the pot, and what the pot is made of. Sanitation is also a consideration when reusing pots and selecting media.
All indoor plants need repotting from time to time. The frequency of repotting depends on the growth rate of the particular plant. Fast-growing plants may need repotting annually, while slow-growing plants may require repotting every two to three years. Some plants (e.g., amaryllis) also thrive when pot bound.
Use a soilless media that contains a combination of organic material (usually peat moss) and inorganic material such as washed sand, vermiculite, or perlite. The ratio of organic to inorganic material should be about 1:2. The organic materials will hold water and the inorganic materials will provide drainage and aeration. These materials are virtually devoid of essential plant nutrients, so fertilizers that include micronutrients are always added to commercial products. Do not use garden soil because it is likely to contain plant disease organisms and provides poor drainage and aeration.
Previously used pots should be scrubbed with detergent and sanitized in a 10% chlorine bleach solution before reuse to minimize disease transmission. Plastic pots are easier to sanitize than ceramic pots or wooden boxes. The pot that you are planting into should be about two inched in diameter larger than the previous pot. Have an ample supply of pre-moistened media available.
The next step is to cover the holes in the bottom of the pot with a paper towel or coffee filter to keep soil from washing out the hole. Despite what your grandma said, forget the rocks in the bottom. Pots with a drainage hole do not need rocks and actually the rocks just decrease the area for roots to grow. You can use a clean rock or potsherd to cover up the drainage hole if desired, but I also recommend using the paper towel or coffee filter.
It is best to repot plants or a tarp where you can salvage spilled media. To begin, hold the potted plant upside-down while knocking the lip of the container sharply on the edge of a table. Hold your hand over the medium, straddling the plant between your fingers. If the plant has become root-bound, you should cut and unwind any roots that circle the plant. Use a clean, sharp knife if cutting is necessary. Remove the top layer of the old medium if you see any accumulated salts. Upon inspection, you may not see any roots and decide the plant does not need repotting. In this case, simply pop it back in the pot and no harm done.
Examine the roots after the plant is out of the pot. The roots should appear firm and white or light-colored. Black, dark colored, squishy or smelly roots are symptoms of root disease caused by overwatering or poor drainage. Rotted roots should be trimmed with a clean, sharp knife or pruners. Roots may also be pruned to keep a plant at a certain size. To do this, you trim off up to 1/3 of the bottom of the rootball. You may also make 3 to 4 vertical cuts through the root mass up to 1/3 deep into the center of the rootball. Again, only use clean, sharp tools.
To repot, put some medium in the bottom of the new pot. Set the rootball in the middle of the new medium. Fill medium around the sides between the rootball. Do not add medium above the original level on the rootball, unless the roots are exposed or it has been necessary to remove some of the surface medium. Gently press or firm the medium with your fingers. After watering and settling, the soil medium level should be sufficiently below the level of the pot to adequately irrigate the plant.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at email@example.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: January 5, 2010
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