Issue: April 23, 2005

Repot houseplants in spring

Question:

Now that the weather is warmer, I want to take my houseplants outside. Should I repot them now or later?

Answer:

Now is a good time to repot houseplants. Some people recommend repotting every spring. If the plants are flowering now and you anticipate a break in the flowering, you may wait until flowering ends.

I admit that I do not repot my plants every year but that is because I try to grow too many plants, and by repotting they grow faster and exceed the space I have for them inside. Repotting will result in more and healthier growth and also more flowers.

Some people are reluctant to repot because they fear damaging the plants. There are several tricks to employ. You may partially replace the potting soil. This is done by carefully teasing some of the soil away from the roots and replacing it with new potting soil. If the plant is not pot-bound (roots which are tightly wrapped around the edge of the pot and filling the soil ball completely), you can try partial replacement of the potting soil. This does not solve salt accumulation problems, so it may not be appropriate for many New Mexico gardeners.

Complete repotting involves removing the plant from its pot and removing much of the old soil from the roots. The soil can be removed by carefully teasing the soil out with chopsticks or a knitting needle. You can also wash much of the soil from the roots with a stream of water. This helps prevent drying of roots. After soil removal, the plant can be placed in a pot one size larger than the old pot (to allow for growth) and new potting soil worked in around the roots. This will replace old salt-laden soil and help avoid salt burn damage in the houseplants. Replacing soil in the spring reduces the risk of salt burn damage in the heat of summer.

Some people try to reuse their old potting soil. This is not a good idea because diseases and salts accumulated in the soil will remain. Fresh, high quality potting soil will produce healthier, more attractive plants.

Choose a potting soil appropriate for the plant. Cacti and succulents are better adapted to a very well-drained potting soil. Look for a potting soil with coarse sand or very fine gravel included. Perlite added to potting soil increases the drainage and air space in the soil that these plants require. Some tropical foliage plants require a soil that remains constantly moist. Choose a potting soil with a high level of compost or peat moss to provide the extra water holding capacity.

Many purchased potting soils contain slow release fertilizers. The presence of fertilizer will be noted on the label on the potting soil. Be sure the fertilizer's nutrient analysis is appropriate for the type of plant you will grow. High nitrogen fertilizers encourage growth of foliage. This is what you want for foliage plants. Flowering plants require higher levels of phosphate. If the potting soil does not have fertilizer already mixed into it, you can use a liquid fertilizer occasionally as you water the plants after repotting. Choose the fertilizer with the analysis appropriate for the plant you are growing and follow the label direction for potted plants.

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Send gardening questions to Southwest Yard and Garden, Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu or at https://www.facebook.com/DesertBloomsNM/. Please include your county Extension Agent (aces.nmsu.edu/county) and your county of residence with your question!

For more gardening information, visit the NMSU Extension Horticulture page at desertblooms.nmsu.edu.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.