News Release Distributed 09/24/10
By LSU AgCenter Horticulturists Dan Gill, Kyle Huffstickler and Allen Owings
September and early October are ideal times for repotting tropical container plants that have summered outdoors. Plants placed outside on porches, patios, decks and balconies grow vigorously through the summer.
This is because excellent outdoor growing conditions, including abundant light, good air circulation and high humidity, encourage the plants to grow enthusiastically. As a result, your outdoor container plants have likely outgrown their pots and have become potbound.
The term potbound is used to indicate plants that have tightly filled their pots with roots. Most plants will tolerate being somewhat potbound. Actually, for some plants, being potbound encourages blooming. This is true for bougainvilleas, for example. And many bromeliads, succulents and cactuses grow better in relatively small pots.
Plants that are potbound generally require more frequent watering and careful attention to fertilizing. Once the roots fill the container, they are limited in the amount they can continue to expand and grow. Still, as long as they get adequate water and mineral nutrients, plants in this condition may remain happy for quite a while.
Eventually, however, plant roots can become so packed in the container that they begin to suffer. They stop growing actively, and as a result, the upper portions of the plant begin to suffer as well. Common symptoms of a plant suffering from an excessively potbound condition include frequent wilting, stunted growth, smaller new leaves, poor-quality flowers or lack of flowers, yellowing and dropping older leaves and signs of nutrient deficiencies.
Many other problems can cause similar symptoms. So how do you determine if a plant is actually potbound?
Look for a dense growth of roots on the soil surface (some surface roots are normal). In extreme cases, the soil may be so full of tightly packed roots that you feel resistance when you try to push your finger into the soil. You also can tilt the pot over and look for roots growing out of the drainage holes.
To be absolutely sure, slide the plant out of the pot and take a look at the roots. If they don’t look like they fill the pot, you can slip the root ball back and do nothing. If all you see is a dense network of roots with little soil showing, this indicates you need to repot the plant. If the plant is still growing well and looks healthy, you may put off repotting until later if you like. But a plant that’s not doing well because it is too potbound should be repotted immediately.
When repotting a plant into a larger container, try not to get carried away. The new pot should generally not be significantly larger than the original one. The new pot should allow only about 2 to 4 inches of new space between the root ball and the sides of the pot.
Over-potting a plant – putting it in a pot that is too large – can lead to root rot from overwatering. And aesthetically, the size of the plant needs to be in pleasing proportion to the size of the pot. In other words, a relatively small plant looks out of place in a relatively large pot.
Don’t cut corners in buying the best possible soil mix when repotting. Most nurseries and garden centers offer quality prepared potting mixes. Make sure the mix is lightweight and drains well. Avoid dark, powdery, heavy potting mixes. Some plants, such as cactuses and orchids, are grown in specialty mixes different from typical potting soils.
To repot the plant, place a layer of potting soil in the bottom of the new pot. Adjust the depth of the soil so that when the plant is placed in the new pot, the top of the root ball will be somewhat below the rim of the pot. When you place the plant in the new pot, don’t pull apart or rough up the root ball the way you may do with landscape plants.
Use more potting soil to fill in the side spaces between the root ball and the pot. Don’t push on the soil with your hands. Instead, if the pot is not too large, settle the soil by lifting the pot a couple of inches off of the table and gently dropping it. In the case of large pots where this is impractical, gently firm the potting soil with your hands, but don’t pack it. Add enough soil to reach the top of the root ball. Finally, water the pot to finish settling the new soil, and you are done.
You may cause some root damage in this process, and plants may undergo some shock after repotting. So place them where environmental conditions don’t put great demands on them. Shady porches and patios, or areas beneath the canopy of shade trees usually are best for getting plants over the trauma of repotting and established in their new container. Allow two to four weeks for plants to become reestablished before moving them back to where they were originally growing outdoors or bringing them indoors for the winter.
Plants generally do not require frequent repotting. Frequency depends primarily on the container size and the growth rate of the plant. Young, fast-growing plants in small pots will need more frequent repotting than older plants in larger pots.
One last point – a potbound plant may be stunted. Generally, this is not necessarily a good thing. However, if a plant has grown as large as you want it to be and would create problems if it grows much larger, you may decide to leave such a plant potbound. As long as it stays reasonably healthy, keeping the plant potbound to reduce the rate of growth can be an advantage in some circumstances.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.lsuagcenter.com/lahouse and www.lsuagcenter.com/lyn.Rick Bogren