January 21, 2017

1 – Container gardens can provides some benefits to New Mexico gardeners, but they can also create new gardening challenges.

Yard and Garden January 21, 2017

Q.

For the last 2 years, I have tried growing vegetables in large containers with no success. These containers are plastic, 18 to 24 inches tall and across. I even purchased seed last year that were bred specifically for containers and they did not succeed. I had placed these containers on my west and south covered porches. I am able to grow geraniums, hibiscus and annuals on the north covered porch. Do you have any suggestions for growing vegetables in containers or is it just too hot here in Roswell?

- Shirley M.

A.

Container gardening offers some benefits to gardeners, but it also brings challenges. Containers may be moved to different locations for aesthetic reasons or cultural reasons. They allow "designing" the soil to the specific needs of the plants being grown. These characteristics of containers allow gardeners to grow plants that that might otherwise not be grown in New Mexico and facilitates growing some plants that we grow commonly grow in our gardens.

However, plants in container gardens may often require more frequent irrigation than plants grown in gardens. That is because the root systems of plants become confined in containers and more quickly extract the water from the soil. Containers can quickly heat the soil along the sunward side of the container to temperatures that kill plant roots. This may significantly reduce the volume of soil occupied by functioning roots. Roots killed by this heat may be more subject to disease attack. When soil in containers dries, it may shrink and pull away from the sides of the containers or form cracks through the soil. This prevents proper moistening of the soil and very fast drying of plants. It is difficult to remoisten the soil and re-expand the soil when this happens. Preventing drying is the best solution. To avoid the problem of soil shrinkage when drying, it is important to use soil formulated for containers (potting soil) rather than soil directly from the garden. The organic matter in potting soil will help prevent the shrinkage because it retains water and will help with remoistening the soil if it has not become too dry.

You mentioned success on your north covered porch, but failure on the west and south covered porches. West and south facing locations are the hottest locations and can be very difficult for plants. This is especially true if the plants are against the wall where heat accumulates and is reflected if they receive direct sunlight. If these locations are shaded most of the day, that creates other potential problems.

Most of our common vegetables (with the exception of corn) utilize the C-3 photosynthetic pathway. That means that at high temperatures they begin a process of photorespiration at temperatures above 85 to 90 degrees. This process wastes carbohydrates produced by photosynthesis. Plants in the shade on a hot porch may "starve" to death when they are hot and not receiving enough sunlight. Some vegetable plants (tomatoes, chiles, beans, squash, and some others) may do well at the edge of the porch where they receive direct sunlight for several hours, but are further away where the heat accumulates against the wall and where it cools more quickly in the evening. Some vegetable plants, such as leafy vegetables and peas will do much better on the north shaded porch. They need less light and prefer much cooler temperatures. Okra and corn will prefer hot sunny locations.

Another characteristic of the porches that you mentioned is that they are exposed to the prevailing southwest winds common in New Mexico in the summer. These are hot, drying winds. Some wind protection may help plants grown on the south and west porches, but sufficient sunlight remains an important factor and the plants should not receive too much shade.

Finally, be sure the soil is properly formulated for containers to prevent shrinkage and failure to remoisten with irrigation. Also, be sure that the plants receive adequate irrigation to compensate for more rapid drying of container gardens. You will also need to supply nutrients more frequently with the irrigation since you should irrigate enough to have significant water drainage from the bottom of the pot. This prevents accumulation of harmful mineral salts in the potting soil, but nutrient minerals are washed from the pot in the water that drains. Do not let water accumulate in a dish or container below the pot to reabsorb into the potting soil. This will greatly increase problems with salt accumulation in the pot.

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html.

Send your gardening questions to Yard and Garden, Attn: Dr. Curtis Smith at cwsmith@nmsu.edu or leave a message at https://www.facebook.com/NMSUExtExpStnPubs.

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist, retired from New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.