Issue: July 26, 2003

When to repot houseplants

How can I tell when it is time to repot my houseplants? Alison K.

There are several reasons to repot houseplants. When plants become pot-bound (when the roots completely fill the pot), the plant may begin to grow less and may flower less. Some plants actually flower better when their roots are pot-bound. A plant which has outgrown the pot may need repotting; you will need to determine the need based on the plants condition.

Many potting soils contain compost, peat, or other organic matter that decomposes over time. This may result in the production of chemicals toxic to the plants or a change in the drainage characteristics of the soil. When this happens, the plant may wilt or develop root rot. Repotting should be done before the plant dies. To catch this problem early, periodically check the roots by gently removing the root ball from the pot and looking for fresh white roots. If all the roots are dark brown and mushy, repotting is necessary. In doing this, you will also be able to determine if the plant is pot-bound.

In New Mexico and many other parts of the country, the tap water used to irrigate houseplants contains dissolved salts (calcium salt, sodium salt, and others). These salts accumulate in the potting soil as the water is used by the plants and as the water evaporates. Salt accumulation in the soil results in damage to roots. In this case, it is important to remove much of the old soil and the salt it contains when repotting. Root rot can develop as roots injured by salt are easily infected by fungus and other disease organisms.

The accumulation of salt can be delayed but not prevented by proper irrigation. The plant should be irrigated sufficiently to completely moisten the soil. From this moist soil, excess water should drain from the pot carrying some excess soil away. Do not let this salt-laden soil be reabsorbed into the pot. Pour the leachate water from dishes under the pot or keep the base of the pot from sitting in the leachate.

These are common reasons for repotting, but there are also other reasons - perhaps the pot is cracked or salts have accumulated on the outside of clay pots. Maybe you want to put the plant in a more decorative pot. These reasons dont always require repotting. You can place a cracked or ugly pot inside a decorative jardiniere (a pretty, often undrained pot). If the jardiniere is unglazed, be careful to keep the base of the pot raised above any leachate water that accumulates after watering.

A final thought! You may want to repot to divide a plant so you will have additional plants that you can share with friends and new gardeners.

Also, please join us on Southwest Yard & Garden, a weekly program made for gardeners in the Southwest. It airs on KRWG in Las Cruces Saturdays at 11:30 a.m., repeating Thursdays at 1:00 p.m.; on KENW in Portales on Saturdays at 10:00 a.m.; and on KNME in Albuquerque on Saturdays at 9:30 a.m.

Send your gardening questions to Yard and Garden, ATTN: Dr. Curtis Smith NMSU Cooperative Extension Service 9301 Indian School Road, NE, Suite 112 Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.

Please join us on Southwest Yard & Garden, a weekly garden program made for gardeners in the Southwest on: KNME-TV Albuquerque at 9:30 p.m. Saturdays, KENW-TV Portales at 10 a.m. Saturdays, and KRWG-TV Las Cruces at 11:30 a.m. Saturdays (repeated at 1 p.m. Thursdays.)