At harvest time, the daily weather report is a call on outdoor growers to “know when to hold'em’’, know when to fold 'em’’. It can be daunting to call a bluff on Mother Nature…. but there is no more addled gambler than the outdoor cannabis farmer.
Ideally, harvest is planned according to trichome ripeness. For outdoor growers in cold climates, the reality is that plants are harvested to prevent damage from frost or mold. When you see the weather, and must play your hand: Ask not just how cold, but how wet, and for how long?
Cannabis can survive sub-freezing temperatures and massive snowfall, unprotected. It can also wilt and die within seconds of exposure to dry, cold air. The key difference is moisture. Frost warnings happen when the night sky is clear and temperatures plummet.
But an off-season overnight blizzard? If it starts with rain, and tomorrow’s forecast calls for sun, then the plants will survive, unscathed. The precipitation coats and protects the plant from brief exposure to freezing temperatures as low as 26f, from our experience on the ranch.
This was the case when a blizzard rolled through southern Colorado in early September, 2020. The storm rained, then sleeted, then dropped over a foot of snow before it stopped, suddenly, around 3am.
The clouds lifted to reveal stars and moonlight cast over a snow-covered landscape. Without a blanket of moisture in the sky, radiant cooling sent temperatures well below freezing in the early morning hours.
Yet sunrise and some gentle shaking revealed the Chemdawg, unphased, un-frozen, alive and well. It survived the blizzard without losing a leaf and thrived for weeks afterward! It proved to be a mild September and October, otherwise ideal weather for such a slow ripening strain.
Citrus farmers have known for generations that water protects against frost. They spray trees with water, forming icicles which, counterintuitively, protect fruit and foliage against freezing. Perhaps this could work for Ganja farmers too?
Physicists of the internet say that water “releases energy as it freezes”. Thus a coating of water will release warmth into the fruit as ice forms around it. I reckon it seems to me water has a high heat capacity-- it takes a lot of energy to change the temperature.
It’s kind of like how a big, heavy tanker truck takes a lot of energy to start and stop, a momentum of sorts. So when a plant is first covered with rainwater, and then snow, it is actually resistant to subsequent hard freeze-- like insulation. Ice cubes form from the outside inward. Thermodynamics aside, the brutal reality is that cold dry air will quickly freeze exposed dry foliage. A layer of water can buy some time in the race against frost.
Luckily mold doesn’t grow well at near-freezing temperatures. However, as plants warm up again, lingering dampness will quickly cause mold and mildew. That’s why it’s important that snowed-in cannabis plants get dry as quickly as possible. Hope for sun the morning after snow.
Even when snow and frost are not in the forecast, beware the dew point on dense foliage and big flowers. Bud rot, at harvest, is a fate worse than death. And it often happens during perfect, dry late-summer weather. That’s because our nights are cold in the high mountain desert. Relative humidity spikes as temperatures drop, especially in the moist micro-climate within the dense foliage of flowering plants.
It is usually the bud attachment sites within the top cola that rot first. Keep in mind, if it is mature enough to rot, then it is mature enough to harvest. If you find mold in one spot, then you will soon find it everywhere. If you catch it early enough, you may still be able to harvest some personal smoke. On the other hand, just don’t. Every gardener knows that the secret to surviving is knowing what to throw away and knowing what to keep.
Every hands a winner, and every hand’s a loser. Unlike frost, there is a lot a gardener can do to fight mold. Canopy management promotes airflow and reduces habitat for mold spores. It is especially important to promptly remove dead leaves from the garden to maintain overall garden hygiene. Check out our articles on canopy management and integrated pest management for more information.