Growing Cannabis by the Moon: How to Use a Lunar Calendar

A cannabis lunar calendar times each grow task to the moon's phases: germinate and transplant around the waxing and full moon, prune and take on pests during the waning moon. There's little hard science behind it, but plenty of growers swear by it, and it starts from a real fact: the moon drives the tides all over the Earth.

According to lunar gardening tradition, the lunar calendar has a big influence on animals and plants, cannabis included. Setting the mysticism aside, here's how the moon is said to affect cannabis plants.

The idea is that the moon regulates part of every plant's photoperiod. Moonlight is believed to stimulate light-sensitive proteins in the plant that set its sap in motion depending on how much lunar light it gets. That's the logic behind building a grow calendar around the moon's phase. 

The info below applies to Argentina, Uruguay and other Southern Hemisphere countries, like southern Colombia, Chile, Bolivia, Peru and Paraguay. The phases themselves are the same worldwide; only the moon's shape and the growing season flip in the Northern Hemisphere.

How the lunar calendar works: the four moon phases

New moon

You'll know it's a new moon when the moon barely shines, so the sap isn't moving. It sinks all the way down the stem to the roots. It's a period of adjustment and rest for the plants, when they recharge before sending sap back through the whole plant. It's the perfect time for pruning or staking, because that's when it'll stress the plant the least.

Waxing moon (first quarter)

This is when the moon's light starts getting stronger, and with it the movement inside the plant, which responds by putting out more foliage and roots. In this phase, sap rises from the roots to the stem and branches. Toward the end of this phase is when we recommend germinating cannabis seeds, so you can plant them on the first day of the full moon.

Full moon

This is when the moon shines brightest, so there's more sap and water moving through the plants, producing more foliage. Root growth starts to slow down. The sap reaches the highest parts of the plant and stays in the main top, branches, leaves and fruit. It's the perfect time to transplant or to plant feminized or regular seeds for stronger growth, because once the sap starts heading back down, the roots have much more room to spread. Pruning is not recommended, though.

Waning moon (last quarter)

As the moon starts to wane, its light fades too, slowing down leaf production. Less sap flows through the tissues, and it starts heading down again, building up in the stem and lower leaves. The hormones behind root growth are in the ideal spot for developing thicker roots. The sap hasn't reached the roots yet, so it's still a good time to transplant, but the plant won't respond as well as it would during a full moon.

How the cannabis moon calendar changes by hemisphere

Even if you know the biodynamic lunar calendar inside out, you need to factor in which hemisphere you're in and look at the moon's shape. During both the waxing and waning phases, the moon looks different depending on the hemisphere:

• In the Northern Hemisphere, the moon is waning when it's shaped like a C. It's waxing when it looks like a D.

• In the Southern Hemisphere it's the other way around: the moon is waning when it's shaped like a D, and waxing when it looks like a C.

Planting by the moon: what to do in each phase

Once you're familiar with the lunar cycles and their supposed influence, it's time to put that knowledge to work in your home grow.

At first, it's normal to struggle to get every task done at exactly the right moment. Don't sweat it. With observation and experience, you'll get better at growing weed by the moon.

A quick heads-up on terms: besides the phases, lunar calendars track an “ascending” and “descending” moon, based on whether the moon rises higher or lower in the sky from night to night over a roughly 27-day cycle. Here's a summary of the ideal conditions for each task in your grow:

Germinating:

Ideally, you'd germinate under a specific moon. For this step, the recommendation is to go with a descending moon during the waxing phase, up to 3 days before the full moon. With cannabis we're mainly after the flowers, so it helps to germinate seeds when the moon passes through an air constellation. Avoid sowing on the day of the full moon, and above all avoid the new moon and the waning moon.

Planting and transplanting:

The ideal lunar window for planting is a descending moon in the waxing phase, which gives you the best conditions to move plants into bigger containers. It's also the go-to moon phase for planting out your germinated seeds.

Pruning:

The big question: which moon should you prune under? A descending moon in the waning phase is ideal, because that's when the plant recovers most easily and you keep stress to a minimum.

Grow-phase fertilizer

If you're following the cannabis lunar calendar, apply natural or homemade fertilizers during a descending moon in the waxing phase. If you use mineral fertilizers, the waning phase is the recommended window.

Bloom fertilizer:

When growing by the moon, apply base nutrients and bloom boosters as the moon passes through air constellations, to help buds form and fatten up. A descending moon in the waxing phase gives the soil the best conditions for absorbing slow-release nutrients. Mineral fertilizers are recommended in the waning phase.

Taking clones:

If you wait until the end of the ascending moon, you'll get strong clones packed with sap. Cutting during this cycle is harder on the mother plant, though, so during the descending moon it's a good idea to apply mycorrhizae to help damaged tissue regenerate and get over the stress.

Planting clones:

If you take your cuttings in the last two days of the ascending moon, you can leave them for at least 2 to 3 days in a container with water and rooting hormone. So when should you plant them? If you follow the steps above, wait for the start of the descending moon. If that lines up with the waxing phase, they're more likely to take, since it encourages roots to appear and develop.

Harvesting buds:

The ideal lunar window for harvesting, to concentrate active compounds, is the waxing or full moon phase, avoiding the day of the full moon itself.

If you harvest during a waning moon, you'll notice your weed has stronger flavors and aromas. Drying goes faster and with fewer problems during a descending moon, but if there's no risk of mold and conditions allow, harvesting during an ascending cycle is ideal.

Harvesting seeds:

To collect seeds, wait until the moon is in its ascending cycle.

Pests and diseases:

A descending moon in the waning phase gives you the best conditions for applying insecticides to cannabis. Fungicides are more effective during an ascending cycle and waning phase.

Below is our 2024 Argentine planting calendar (Southern Hemisphere) to guide you when planting or handling any other part of your grow:

LUNAR CALENDAR 2024 (SOUTHERN HEMISPHERE)