Ask ten gardeners about the moon and you get three who swear by it, three who roll their eyes and four who do it just in case. We sit in the fourth group, and we also publish a moon calendar, so we owe you a straight look at what the evidence says. Short version: it is thinner than most calendars let on. Longer version is below, plus a way to find out for your own garden.
What the tradition actually says
Two different systems get mixed up under the one name, so it helps to pull them apart.
The phase system follows the moon growing and shrinking. Our calendar splits the month into four stretches: new moon to first quarter for leafy crops, first quarter to full moon for fruiting crops, full moon to last quarter for root crops, and last quarter to new moon as a rest period for weeding, composting and soil preparation. The idea is that sap rises while the light is growing and falls while it is shrinking.
The sign system comes from the biodynamic movement and the work of Maria Thun. It ignores the phase and tracks which zodiac constellation the moon is passing in front of. Each sign is tied to an element and a plant part: fire for fruit, earth for roots, air for flowers and water for leaf.
The two cycles run on different clocks, so a day that is good by phase can be a poor one by sign. Our calendar shows both. That alone tells you the tradition is more of a menu than a law.
What the evidence says
There are two usual explanations for why the moon would matter to a seed, light and gravity. Neither holds up well.
Light. A full moon on a clear night delivers roughly 0.05 to 0.3 lux. Direct midday sun is somewhere around 100,000 to 120,000 lux. Our arithmetic, not a measurement of ours: that makes the sun hundreds of thousands of times brighter, up to millions of times at the dim end of the moon range. Seeds in the soil do not see the moon at all.
Gravity. We looked for a mechanism that plant scientists accept for how the moon’s pull would eventually change germination or growth in a garden bed, and we could not find one.
The trials. The supportive work comes mostly from inside the biodynamic movement itself: trials on radishes and carrots, and later reviews written by supporters, report differences in yield depending on where the moon is. The summaries we could find describe those effects as small and not consistent from one trial to the next. We did not find independent, repeated trials that settle the question either way.
One honest limit on our side. We read summaries and could not get hold of every original paper, the 2001 Kollerstrom and Staudenmaier review among them, so treat this as our reading of the secondary sources and not as the last word.
What matters far more than the moon
Sowing in the wrong month will cost you much more than sowing on the wrong day. Soil temperature, moisture, the season and whether the variety suits your climate decide most of what comes up. If the moon says wait but the heat breaks on Thursday, sow on Thursday. That is also how we wrote the line on our own moon poster: the season picks the month, the moon picks the day.
So why keep a moon calendar at all?
Because a rhythm gets people into the garden. A calendar that says leaf crops this week, roots next week and rest days for weeding is a decent prompt to do the jobs in order, even if the moon does nothing. Plenty of good gardeners use it exactly like that, and nobody has been hurt by weeding on a rest day.
A small practical thing from living here: in Australia the growing moon is lit on the left, not the right as on many overseas calendars. And overseas calendars often list phase times in their own clock, so a full moon late on a Sunday night in London lands on Monday morning in Brisbane. If you use an overseas calendar, check the date against your own clock.
A fair test you can run in your own bed
Rather than take our word, or anyone’s, you can find out. It costs one packet of seed.
- Pick one quick crop. Radish is a good one. It is usually up in about a week and ready in about a month, so you get an answer before you lose interest.
- Use one packet and one bed. Do it in the weekend, so you can mark two short rows side by side. Sow 20 seeds in each, at the same depth, in the same soil, and water them the same.
- Sow one row on a day the calendar rates best for roots, and the other row three to five days later on a day it rates poorly. Label them. Weather will differ a little between the two days, and that is a real limit of this test.
- Count and weigh. Count teh seedlings at ten days. Weigh the harvest when they are ready.
- Repeat it three or four times across the season with different crops.
A word on reading the result. With 20 seeds per row, a gap of two or three seedlings is inside the normal noise, and one test proves almost nothing. This is our own reasoning about small samples, not a rule from a textbook. What would count is the same row winning, by a clear margin, in most of your repeats. If that happens, you have found something worth knowing about your own soil. If it does not, you have saved yourself some fuss.
Write the dates and counts down as you go. A note in the phone is fine, and a printed record page beside the crop is better, because next year you will not remember.
Want the whole year laid out?
The Garden Year 2027 puts the full 2027 moon calendar next to a month by month plan for your climate zone, with a page for every crop and room to write down what really happened. That is exactly the record your moon test needs. There is an edition for each of the seven Australian climate zones.
Where our facts came from
- Moonlight and sunlight illuminance ranges: the Wikipedia pages on lux and illuminance orders of magnitude. The ratio is our own division of those figures.
- Biodynamic and sign system background and the reported trials: secondary summaries only, including the Kollerstrom and Staudenmaier lunar and sidereal crop yield review (2001), which we could not read in full.
GardenBuddy.au, built for subtropical vegetable growing at Dayboro, QLD. More about the project.
