Tolerance of Moringa oleifera to Freeze Events

Through funding from the Howard G. Buffett Foundation, ECHO has completed an initial year of research in South Africa (Limpopo Province). Our goal is to conduct research applicable to farmers in Sub-Saharan Africa. Part of our research has been to study a moringa/legume intercropping system, in which edible, green manure cover crops are grown between rows of moringa trees. What we have found so far may be of interest to those working in higher altitude tropics, or in any area where moringa grows well during the rainy season but must endure short periods of freezing temperatures during the dry, winter months. 

Recognizing that freezes commonly occur in South Africa, our first objective with the moringa/legume study was to see if we could successfully plant and then overwinter moringa trees in the field. 

Moringa seeds were planted in the field in mid December of 2010. The seeds were planted 20 inches (50 cm) apart (with a plan to later thin to 39 inches/1 m) in 197 feet (60-m) long rows spaced 3.3 yds (3 m) apart. Soil moisture was supplied with drip irrigation. Anticipating freezing temperatures, we mulched the base of the trees with straw in July 2011. Air temperatures were monitored with a weather station in the field that logged a reading every 5 to 15 minutes. Here is what we observed: 

Between 27 May and 13 August 2011, there were a total of 44 freeze events. Six of the events were single observations in which the temperature dipped down to freezing for only 5 to 15 minutes. The average freezing temperature was -1.42 °C (29.4 ºF), with a minimum of -5.30 °C (22.5 ºF). The majority of freezes occurred between 6 and 7 A.M. The longest freeze event lasted 8 hours and 10 minutes. The average duration, excluding single-observation freeze events, was 2 hours and 57 minutes. 

During the winter, the above-ground portions of the trees died back, with green tissue existing only at the base of the trees. Considering the number of freeze events, we wondered if we would see any regrowth when the temperatures warmed back up in September/October.

We were pleasantly surprised in late October to find new growth on 33% of the trees. Shoots were coming up from the base of the trees, near ground level, or even from below ground. By January 2012, regrowth was found on 49% of the trees. Tim Watkins, who directs ECHO’s Agriculture Operations department, commented that he has observed similar moringa response to freezes here in southwest Florida. 

To summarize, our findings suggest that nearly 50% survival can be expected with six-month old, mulched moringa trees in areas that experience brief periods of freezing temperatures. To maximize moringa survival during freeze events, we recommend 1) establishing the trees early in the growing season to maximize the amount of woody tissue (which has a better chance of withstanding freezes than young, green tissue) and 2) mulching the base of the trees.