Salt Problems with Houseplants, Caliche Soils, and Get Those Bulbs in the Ground ASAP!

Southwest Yard & Garden by Dr. Marisa Thompson

Tulips and daffodils offer tons of color with remarkably low water requirements. This year at the NMSU Agricultural Science Center at Los Lunas we’ll also be sampling bulb blossoms for presence of beneficial insects. Stay tuned! Photo credits M. Thompson.

Reprints from years past. Written by Dr. Curtis Smith, retired NMSU Extension Horticulture Specialist, with additions by Dr. Marisa Thompson. 

Question from 1997: What does it mean when they say our soil is calcareous?

Answer: The term calcareous refers to the abundance of calcium, or lime, in our soil. This is due to the fact that our dry environment has not resulted in the leaching of calcium and other salts from our soils. Some of these salts, such as sodium, can be toxic to plants at the level found in some New Mexico soils. Calcium, however, is not toxic, but it does alter the pH, or acidity, of the soil, making it difficult for some plants to obtain the nutrients they need. Other plants, especially those native to calcareous soils, have no problem and flourish in our soils. The main message to remember is that we do not have to add lime to our soils like they do back east. The main component of wood ash is calcium carbonate, so it’s best to dispose of ashes either in the garbage or in places where you do not want plants to grow, like the middle of your driveway. For more information, see NMSU Extension Guide A-151, “Growing Plants in Caliche Soils”.

Question from 2008: Each spring I repot most of my houseplants. This year I have noticed quite an accumulation of salts and other deposits on the top of the soil and around the edges of the pots. I guess it has always been there, but now I see it and wonder if there is any way to reduce this when I repot.

Answer: If you just repot by moving the old soil into a larger pot and adding new soil around it, you do carry the accumulated mineral salts from one or more years of growth into that new potting soil. This residual salt can do damage to your houseplants, so your concern is valid.

There are a couple of ways to deal with this problem. The first is to remove all or most of the old soil when you repot. When you remove this soil, there will be some damage to the root system. Some plants will tolerate this "root pruning," while others will be injured. Minimize root damage when removing the soil by carefully teasing the soil away with chopsticks or other implements, or take the plant outside and gently wash the soil away with water from the garden hose. If you cannot get all the soil removed, you will still remove much of the accumulated salt using these techniques. The washing technique also removes salts by dissolving them from any soil that remains. It also keeps the roots moist while you are removing the soil so they will not be damaged by drying. Do this in a shady place on a warm spring day so the roots will not be harmed by sunlight or by cold.

Once you have removed the soil as well as you can, you can repot into a new pot or the old pot if it has been cleaned thoroughly and well rinsed. By removing the soil, you may not have to move the plant to bigger and bigger containers each year. This helps keep the size and weight of your houseplants manageable. If the plants are growing rapidly, you may need to use a larger pot, but you have the option of reducing the rate at which the pots increase in size and weight.

The new soil you use should be appropriate for the plants you are growing and should be disease-free. Now you are ready to return your plants indoors or to let them spend the summer vacation outside in a shady location.

Question from 2011: Can I plant tulips now? I received some tulip bulbs for Christmas but never got them in the ground.

Answer: In most parts of the state it is too late to plant bulbs and get flowers this year, but they are better off in the ground rather than sitting on a shelf somewhere until next fall. If you plant them now, they may bloom. However, they may just produce leaves and you may have to wait until next year to see them bloom.

For more gardening information, including decades of archived Southwest Yard & Garden columns, visit the NMSU Extension Horticulture page (http://desertblooms.nmsu.edu/), follow us on social media (@NMDesertBlooms), or contact your County Extension office (https://aces.nmsu.edu/county).

Marisa Thompson, PhD, is the Extension Horticulture Specialist for New Mexico State University and is based at the Agricultural Science Center at Los Lunas.