Repotting Houseplants, Wind Gusts, Branch Die-Back
July 17, 2021
Reprinted columns by Dr. Curtis Smith
This week I've selected three Archived Columns to reprint based on recently received questions.
- My sister texted photos of her houseplants, wondering how to tell if it's time to repot them.
- Wind gusts all over the state have taken out tree limbs and left owners worried about what to do next.
- Branch die-back, especially on older trees, is also worrying owners and may have been caused by drought stress over the past winter.
The advice my predecessor Dr. Curtis Smith provided 18 summers ago is just as timely and helpful as ever.
Archived column: July 26, 2003 - When to Repot Houseplants
How can I tell when it is time to repot my houseplants?
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 that has outgrown the pot may need repotting; you will need to determine the need based on the plant's condition.
Many potting soils contain compost, peat, or other organic matter that decomposes over time. This may produce chemicals that are toxic to the plants or may cause 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 plants use the water 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 because roots injured by salt are easily infected by fungi 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 out 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 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 don't 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 (and therefore porous), 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.
Archived columns: August 2, 2003 - Broken Branches
I had a large branch break off a tree from heavy winds. The tree is otherwise in good health. Do I need to treat the exposed cut on the tree, or can I just leave it to weather?
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 ripped as the branch fell. If that occurred, then only cut to create a clean (rather than ragged) wound. Do not use pruning sealer materials. They will help disease organisms grow better in the protected, humid environment below the sealer. An unpainted wound (especially one outside the branch collar) will be "compartmentalized" by the tree to prevent the entry of disease organisms and insects into the trunk. Some people want to put a bandage on the wound, but this isn't necessary.
Globe Willow Branches Dying
I live in the Albuquerque South Valley near one of the ditches. My problem is that I have two very beautiful globe willows in my front yard, and one of them is dying. They are in the middle of my lawn, so they get a lot of water. They are close to nine years old and have been doing great until about a month ago. At least 8 to 10 big branches are turning brown, and more seem to be following that pattern.
When you say the trees are well watered, I assume you irrigate by flooding your yard from the ditch. Trees do well under that situation except in the winter when the ditch is not flowing. From what you describe, I think your problem developed during the winter. Trees need to be irrigated once a month in the winter, especially in late January and February. It was very dry last winter. Injury resulting from winter drought appears as dying branches in the summer. Stressed trees attract borers, which may also be doing damage. If you find that borers are present, take a sample to your county Cooperative Extension Service office (https://aces.nmsu.edu/county/) to have the insects identified. The Extension agent should then be able to tell you the steps you should take to prevent further damage by borers. In the meantime, be sure the trees are watered deeply (to a depth of 2 ft) about once every two weeks in the growing season and once a month in the fall and winter.
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, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!