Proper soil for citrus in half wine barrels

Question:

I have successfully grown Meyer lemon and key lime plants in half-wine barrel tubs. One of the key limes has finally started to flower after five years of being planted from seed. However, one of them did rather poorly. The soil had bad drainage and got packed and moldy at the bottom of the tub. I heard that rich humus potting soil isn't necessarily the best and that they prefer rocky/sandy soil with fewer nutrients and more alkaline. Is this true? What do you suggest as the best soil for these little fellows?
- Scott W.

Answer:

One advantage of growing plants in containers is that we can "engineer" the soil to meet the specific need of the plants we will grow. However, we often just use "potting soil", which may result in problems. Some plants will grow well in a high humus content soil while others may thrive for a while. As the soil compacts and becomes water-logged, as you observed, some plants begin to decline.

Another factor to consider is that soil in a container does not always behave in the same manner as soil in the open ground. There are several reasons for this. One is the fact that the soil is subject to more rapid wetting and drying because of its small volume and location above ground (more exposed to sun and wind). As the soil dries, it may pull from the sides of the container and resist moistening again when irrigated. This may result in drying of the plant.

In your case, the opposite may have resulted. The container may have developed a "perched water table". In this situation there was an accumulation of water at the bottom of the barrel because of plugged drainage holes or because the water cannot easily drain when there is a change in soil texture (pore size). The increased water content in the bottom may have resulted in more rapid decomposition and packing of the soil particles, further reducing drainage.

It helps to know the soils in which these plants grow best. As you mentioned, soils with good drainage and less organic matter may be appropriate for your citrus. Many locations commercially growing citrus have well-drained, sandy or gravely soils. There may be some organic matter but not as much as in potting soil. These areas often have high calcium content in the soil (more alkaline than potting soil). This guides you in engineering your soil for them. You can start with soil from your garden or with potting soil. If you begin with potting soil, add coarse sand (sand-blasting sand) or small gravel (aquarium gravel) to increase drainage. If you begin with garden soil, you may need to add these elements in addition to compost or potting soil. Generate a soil that readily lets the water pass through, yet retains some of the water. The water will provide sufficient alkalinity. (Most New Mexico water contains dissolved calcium salts and sometimes sodium salts.) A soil that allows surplus alkalinity to wash away with water through drainage will prevent the salts from accumulating to harmful levels.

In our climate, using large but portable containers permits us to grow citrus plants and other plants that cannot be grown outside through the winter. I hope you succeed and enjoy the fruits of your labor.

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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: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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