March 14, 2015

1 - Mixing things that "grow up" with those that "grow down."

Yard and Garden March 14, 2015


A gardener was telling me about planting radishes with other crops. She said that mixing things that "grow up" with those that "grow down" is a good practice. Is this correct?

-Boe L.



Your gardener friend was talking about companion cropping. This is the practice of growing several different plants together. There has been some scientific/published research regarding this and a lot of home garden experimentation with this topic.

An old gardening practice used by the Native American gardeners for generations in Southwestern cropping is called the "Three Sisters" garden technique. In this garden method corn, beans, and squash (and in the last hundred years or so - tomatoes and chiles) are planted together. This takes advantage of the different physiological and nutritional differences of each plant. The corn can use full sunlight, the other plants benefit from some shade provided by the taller corn. Vining beans can use the corn plants for support. These plants have different rooting depths and can share the soil and they place somewhat different nutrient demands on the soil. The taller plants help reduce wind drying of the lower plants; the lower plants serve as a living mulch preserving water for the other plants as well as themselves.

This ancient gardening technique for the Southwest illustrates some of the principles of successful companion cropping. The plants utilize different space (above and below ground). They have somewhat different nutrient requirements and different root zones so they coexist within the soil. Some provide benefits for others; corn shades and shelters other plants from the wind, some serve as living mulch conserving soil moisture, some (beans) capture nitrogen from the air and release it to the soil when they die, benefiting other plants the following year.

There are other benefits mentioned. The key is minimized competition and maximized cooperation - proper spacing helps with this and consideration of different plant requirements is important.

Plants with deeper root systems may often grow successfully with shallower root systems. Plants that germinate quickly may help break crusting soils to allow more slowly germinating seeds to emerge from the soil. Radishes are often used for this purpose because they germinate quickly. Radishes also have shallow root systems and mature quickly and are harvested early.

There are reports of onions repelling insects and protecting other crops. Other fragrant plants are suggested for this purpose. The results from this type of companion planting are often mixed. However, there is some evidence that plant odors may provide some protection, if there are relatively few plants being protected. A few high odor plants among other plants may not provide the desired level of protection. Insects do often find their target plants by their odor, but their sense of smell (chemo-sensing and chemotaxis) is sophisticated and may not be easily confused.

Differing plant nutrient requirements has been studied in detail and is published in many textbooks. Plant space utilization and harvest timing is also well known and can be used in helping you determine proper companion plants. Experimenting to see which combinations work well in your soil and climate is a good thing to try. Best wishes as you maximize your garden space utilization with companion cropping.

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:, office: 505-865-7340, ext. 113.


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

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!