If your houseplants have been growing rapidly during spring and summer, it may be time to repot them into larger containers.
More light during spring and summer often brings more plant growth, said Deb Brown, horticulturist with the University of Minnesota Extension Service.
"When repotting into larger containers, the rule of thumb is to choose pots only one size larger than the current ones," said Brown. "Going from a small container to one much larger increases soil volume enough that the soil will stay wet longer when you water. Roots may suffer as a result."
Brown recommends a container with at least one drain hole. Cover that drain hole with an irregularly shaped pebble or piece of broken clay pottery. That will make it possible to keep soil in but allow excess water out.
After adding fresh potting soil, transfer the plant -- roots, soil and all. Then firm more soil gently between the root ball and sides of the container. Otherwise, water will run too quickly down the inside walls of the container, rather than thoroughly soaking the entire soil mass, said Brown.
An alternative to repotting for some houseplants is to root prune them to control growth and keep them in the same containers year after year. Knock the plant out of its pot and shave one-half to one inch off the soil and roots from both the bottom and sides of the soil mass, said Brown. Add fresh potting soil and replace the plant, firming soil as described previously.
When root pruning, it's important also to prune the top growth slightly. This keeps the roots and foliage "in balance," said Brown.
"Not all houseplants may be pruned," she said. "It's not a good idea to prune plants, Norfolk Island pines, yuccas or most houseplants that have a strong central trunk with little or no branching."
The university's Yard and Garden Clinic has experts to answer questions on horticulture, plant disease and insect problems between 9 a.m. and 3 p.m. weekdays. Call (612) 624-4771 in the metro area or (888) 624-4771 from outside the metro area. There is a $5 fee, which can be billed to a major credit card.
The clinic is one of the services available through Yard and Garden Line. Also available are free recorded messages 24 hours a day from Info-U. And at no charge, callers can request a return call from a Master Gardener volunteer in their county or can speak to a wildlife expert.
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