Extension Educator, Horticulture
Repotting houseplants is not for wimps or kind-hearted gardeners. When done properly your work area should be strewn with plant parts and soil. Repotting can be an invigorating process for plants and us. But when should plants go through this invigoratingly traumatic experience? Every three to five years is a good rule of green thumb or look for these indicators:
The best time to repot plants is when they are actively growing, usually spring through summer so now is a great time.
Now that we know when and why, it's time for how. Hopefully the plant isn't too big to lift and turn upside down. Large plants take a little different technique and the help of a friend. To get a plant out of the pot turn it upside down with one hand on the soil surface with the plant stem between your fingers. Put your other hand on the bottom of the pot. Now with a sharp downward motion support the plant and soil with one hand as you pull the pot off with the other hand. Most plants will require you to hit the edge of the upside down pot onto a hard surface such as a workbench.
Once the plant is out of the pot, be sure to examine the roots. The roots should appear firm and white or light-colored. Black, dark colored, squishy or smelly roots are symptoms of root rot. The plant has probably been over-watered at some time.
Any rotted roots should be removed. To keep a plant at a certain size, trim off up to 1/3 of the bottom of the root ball. Also, make 3 to 4 vertical cuts through the root mass - up to 1/3 deep into the center of the root ball. Be sure to cut through any roots growing in a circular pattern around the root ball. Roots should at least be pulled apart before repotting. The top of the plant can also be trimmed.
Select a pot that is about one to two inches bigger than the original. A plant in a 4-inch pot would go into a 6-inch.
Next step cover the holes in the bottom of the pot with a paper towel or coffee filter to keep soil from washing out. Despite what your grandma said, forget the rocks in the bottom. Pots with a drainage hole do not need rocks.
Now add some soil to the bottom of the pot. Tear off the top edge of the root ball as you set the plant in its new pot. Fill the pot to the rim with soil mix. Once watered, the soil should settle to leave a half-inch to inch space between top of the pot and the soil for proper watering.
The goal is to have the newly repotted plant sit in the new container at the same level it was in the old container with some new soil around and on top of the old soil ball. Water thoroughly after planting.
The weather is perfect for repotting houseplants outdoors. However, keep in mind most houseplants are tropical. In spite of our recent "tropical" weather we continue to have a reasonable chance of frost. So let your houseplants enjoy playtime outside, but if the forecast is for less than 45 degrees take them to a protected area.