Our sun has special significance in the gardening world. It offers sunlight, which plants use to generate energy and directly influences plant lifecycles in a variety of ways.
Have you ever considered the role of the moon in plant growth? Historically, many agricultural and gardening practices were planned based on the lunar cycle. Before the invention of the various time tracking technology we are indulged with today, the phases of the moon were an important aspect of time keeping. Ancient peoples around the globe carefully tracked the moon and other celestial bodies to understand seasonal timing and to plan various activities of daily life.
If you aren’t tuned in to the phases of the moon, we are due for a full moon tonight. The light of the full moon is signal to many that it’s time to plant, harvest or do other activities in the garden. Beliefs and traditions surrounding the lunar influence on plant and animal life have existed for as long as human culture, yet few have scientific support in their application.
Once such tradition that ties the lunar cycle to plant cultivation is the act of “planting by the signs”. This historically popular practice is based on the premise that the moon impacts water on earth and cycles of the moon will consequently impact plant growth. Therefore, planting and harvesting recommendations were based on the phase of the moon and the specific sign of the Zodiac for that day, thus the term “planting by the signs.”
The moon certainly does impact the tides, which is attributed to the gravitational force it applies to earth across the lunar cycle. This relationship has much scientific support and has been accepted as fact in the basic physics of the natural world. However, the science behind a lunar influence on plant growth is difficult to find.
A recent review paper in the journal Agronomy put this relationship to the test using current scientific understanding of lunar physics. Researchers reviewed over 120 scientifically supported references to assess whether or not the moon’s influence on earth extends beyond tidal movements to significantly effect the lifecycle of plants.
This review looked at the moon’s gravity and assessed whether or not its influence on earth might affect plant life. We know that the earth’s gravity impacts plant growth, as evidenced by simple observations of potted plants tipped on their side. Both roots and above ground stems have been shown to react to gravity and correct their growth accordingly when pots are oriented differently. So, a similar influence from the moons gravitational pull may affect plant life as well.
However, the moons gravity as it influences earth is approximately 300,000 times less than the effect of the earth’s own gravity and researchers concluded that this influence is so negligible it cannot have significant influence over plant processes.
They compared the moon’s gravity to other factors in plant life, such as the force required for the capillary action that moves sap upward in plants. In the case of capillarity, the force of the moon’s gravity was concluded to be “completely imperceptible” when compared to the force required to move sap up plant stems.
Researchers also looked at other aspects of the moon’s influence on earth, such as the light it reflects from the sun. This lunar illuminance, during a full moon, was found to be 128,000 times less than sunlight provides. Even when assessed in the context of the most sensitive plants, lunar illuminance was not found to be a significant player in photosynthesis or plant lifecycles.
Based on this review, and the factors we know about the moon’s influence on earth, there was no consistent relationship identified that supports a lunar influence on plant life. However, some interesting research was reviewed that eluded to other more tangential relationships. In one case, a middle eastern shrub was found to produce more pollen under a full moon which correlated with higher pollination success since it attracted pollinators better able to navigate by full moonlight.
Perhaps there are some underlying relationships worth further investigation? Researchers did conclude that additional research is needed, especially in light of the widespread global traditions surrounding perceived lunar-plant relationships. While additional research may uncover new and interesting aspects, it also serves to promote critical thinking and use of the scientific process over simply following tradition.