This week, I selected three archived columns reprint based on questions received recently.

1. My sister texted pictures of her houseplants, wondering how to know if it’s time to repot them.
2. Gusts of wind across the state destroyed tree branches and left homeowners worried about what to do next.
3. Branch dieback, especially on older trees, is also a concern for homeowners and may have been caused by drought stress over the past winter.

The advice my predecessor, Curtis Smith, gave 18 summers ago is still timely and helpful.

When to repot houseplants

Chronicle on July 26, 2003

Question: How do I know when it’s time to repot my houseplants?

Reply: There are many reasons to repot houseplants. When the plants become bonded to the pot (when the roots completely fill the pot), the plant may start to grow less and may flower less. Some plants flower best when their roots are tied to the pot. A plant that has grown out of the pot may need to be repotted; you will need to determine the need based on the condition of the plant.

Many potting soils contain compost, peat, or other organic matter that decomposes over time. This can produce chemicals that are toxic to plants or change 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. By doing this, you will also be able to determine if the plant is related to the pot.

In New Mexico and many other parts of the country, tap water used to irrigate houseplants contains dissolved salts (calcium salt, sodium salt, and others). These salts accumulate in the soil as plants use the water and the water evaporates. The accumulation of salt in the soil damages the 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 because salt damaged roots are easily infected with fungi and other disease-causing organisms

Salt build-up can be delayed but not prevented by proper irrigation. The plant must be sufficiently irrigated to completely moisten the soil. From this moist soil, the excess water must drain from the pot, thus washing away the excess soil. Do not allow this salt-laden soil to reabsorb into the pot. Drain the leachate from the dishes under the pot or prevent the base of the pot from sitting in the leachate.

These are common reasons for repotting, but there are other reasons – maybe the pot is cracked or salts have built up on the outside of the clay pots. Maybe you want to put the plant in a more decorative pot. These reasons do not always require repotting. You can place a cracked or ugly pot inside a decorative planter (a pretty pot that is often undrained). If the planter is unglazed (and therefore porous), be sure to keep the bottom of the pot elevated above any leachate that collects after watering.

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

Broken branches

Chronicle on August 2, 2003

Question: I had a big branch of a tree broken because of the strong winds. The tree is otherwise healthy. Do I have to treat the cut exposed on the tree, or can I just leave it in the weather?

Reply: You can cut the branch cleanly just outside the “branch collar” (the slightly swollen area where the branch meets the trunk). Do not cut inside the branch collar unless the bark has torn when the branch falls. If this happens, only cut to create a clean (rather than jagged) wound. Do not use pruning sealer. They will help pathogenic organisms to thrive better in the protected and humid environment under the sealant. An unpainted wound (especially one on the outside of the branch collar) will be “compartmentalized” by the tree to prevent pathogens and insects from entering the trunk. Some people want to put a bandage on the wound, but it is not necessary.

Dying globe willow branches

Chronicle on August 2, 2003

Question: I live in the South Albuquerque Valley near one of the ditches. My problem is that I have two very beautiful globular willows in my yard, and one of them is dying. They’re in the middle of my lawn, so they get a lot of water. They are almost nine years old and are doing well until about a month ago. At least 8-10 large branches turn brown and others seem to follow this pattern.

Reply: When you say the trees are watered well, I assume you are irrigating by flooding your garden from the ditch. Trees do well in this situation, except in winter, when the ditch is not flowing. From what you describe, I think your problem developed during the winter. The trees should be irrigated once a month in winter, especially at the end of January and February. It was very dry last winter. Injuries resulting from winter drought appear as dying branches in summer. Stressed trees attract borers, which can also cause damage. If you find that borers are present, take a sample in your county Office of the Cooperative Extension Service identify insects. The extension worker should then be able to tell you what steps to take to prevent further damage from the borers. In the meantime, make sure the trees are watered deeply (to a depth of 2 feet) about once every two weeks during the growing season and once a month in the fall and winter.

For more information on gardening, visit the NMSU Extension Urban Horticulture page at http://desertblooms.nmsu.edu/ and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/. Find your local cooperative extension office at https://aces.nmsu.edu/county/.

Marisa Y. Thompson, Ph.D., is an Urban Horticultural Extension Specialist in the Plant Science Extension Department and is based at the New Mexico State University Agricultural Science Center in Los Lunas.

Courtyard and garden more southwest: