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  • Professor Sprout

The Weed In The North! Mold Resistant Cannabis Strains For Outdoor Northern Growers

Updated: Oct 28, 2019

Hi Professor Sprout,

I'm just thinking ahead to next spring. What are the hardiest mold-resistant and cold tolerant strains on your website? I'm thinking of indicas mostly, but hybrids and sativas also interest me.

From what I've seen, KK (Korengal Kush) and PBH (Peanut Butter Herijuana) seem like they'd allow for some good air flow, while the shorter, bushier ones like A98 (Angel ’98) and GDP (Grand Daddy Purple) might not fare as well. Then again, I'm a rookie so I don't really know for sure.

I am located in eastern Canada and the weather has turned cold, damp, and my plants still have weeks to go before they’ll be ready to harvest. I need something that can withstand our Canadian climate.


Yes, Lucky 13 Seed Company’s Korengal Kush and Peanut Butter Herijuana do fare well outdoors, especially the PBH. Peanut Butter Herijuana produces a sativa-looking phenotype that initiates flowering very early and finishes before it gets too cold and damp. All phenos produce dense golfball-like buds with excellent internode spacing that allows plenty of airflow to wick away moisture and prevent rot.

Korengal has some tough genetics and being a high altitude landrace from the Himalayas is certainly more tolerant of cold temperatures when planted directly in the ground where the roots stay insulated.

Korengal Kush Bud
Korengal Kush's Himalayan genetics make it resistant to colder climates.

However, the weather we've been dealing with in western Canada (and the larger part of the country) for the past number of years has been trending towards shorter summers with cold and damp conditions that arrive almost overnight. This year it literally went from warm and sunny one day, to cold and damp the next. Summer was gone in less than 24 hours.

As a result of this new trend, many strains that traditionally would ripen without issue are having trouble reaching maturity. And if they do, the buds are often destroyed by the dreaded moldy “Bud Rot”. Botrytis is the technical term for this nasty disease, and it is triggered by rain and high humidity causing excessive moisture buildup in the buds that creates a breeding ground for this nasty shit.

Genetics do play a part in mold resistance, but the sad fact of the matter is that Cannabis is just not well adapted to a cold and wet climate and almost all strains will be prone to molding and rotting if the environment is not kept dry and warm.

But fear not! There are options for those of us who wish to grow outdoors in the northern latitudes. The first thing to consider is planting in containers. If you’re planting directly in the ground and the weather turns ugly, you’re stuck where you are. Yes, you could erect a makeshift plastic greenhouse, but this is only going to increase the already deadly-high humidity. In containers you have the option of moving the plants to a warm and dry indoor location to finish ripening.

Lucky 13 Outdoor Cannabis Plants
Early flowering Cannabis strains take advantage of ripening when it's warm and sunny.

Even just bringing the plants indoors to a perfectly dark garage at night and moving them back outside during the day can give you an extra couple of weeks of ripening time; which may be all you need if you’re growing a fast flowering Indica. However from personal experience I can tell you, this is a monumental pain in the ass if you’ve got more than a few plants to handle. This also means you aren’t going anywhere for the time it takes your plants to ripen. You’re going to be their bitch until they’re finished. No weekend getaways, no coming home late at night, you’re on lockdown and at the mercy of your precious plants.

The next option is a proper greenhouse. This would allow you to avoid artificial lighting entirely, but may still require supplemental heat, and most definitely will require dehumidification and plenty of air circulation. I realize for many people a full-sized greenhouse with heat, fans, and dehumidification is somewhat of a pipe dream (pun definitely intended) so the next option is early-flowering genetics.

Early strains can take the shape of varieties that flower automatically after a certain number of days of growth no matter the time of year, or strains that begin blooming earlier in the season, and thus ripen before the weather turns ugly.

Lucky 13 Frostberry Cannabis Strain
Frostberry cola starting to put on weight early in bloom.

While auto-flowering genetics have improved somewhat in recent years, many still suffer the same issues that have always plagued autos: poor yield, leafy buds that lack density and resin, ho-hum potency, and mediocre medicinal value. Plus you can’t clone the little bastards, so you’re going to have to constantly buy new seed; which is great for us seed companies, but not great for you, the customer.

I have grown my share of auto-flowering varieties over the years and while it certainly is handy being able to harvest 70 days after planting while the weather is warm and dry and mold is just a faint whisper of a threat; I have yet to find myself reaching for a jar of “auto-bud” when I’ve got something else to choose from like my recent batch of Peanut Butter OG in my stash. Your results may vary, but this is a common sentiment among Cannabis connoisseurs.

To understand this topic better, you need to know how Cannabis initiates the flowering stage of it’s life cycle. Most traditional varieties start flowing somewhere around the autumnal equinox (last weeks of September in the northern hemisphere) when the days and the nights are of equal length at 12 hours of light and 12 hours of darkness. The decreasing amount of sunlight triggers hormones that tell the plant that winter is coming and that it is time to start blooming to reproduce.

Every strain has a different set-point at which blooming actually begins, but virtually all strains flower under 12 hours of uninterrupted darkness. But here is the big problem; if you live in the colder regions of the globe, by the end of September the weather has already turned to shit and you’re plants are only just starting to flower. At this point you’re going to need a lot of luck and plenty of cooperation from mother nature to get them to ripen to completion. In my estimation, nearly 80% of outdoor bud harvested in the northern United States and most of Canada is underripe, which is one reason why outdoor bud has such a bad reputation.

Peanut Butter OG Outdoors
Lucky 13 Seed Company's Peanut Butter OG getting massive outdoors. Yes that is just one single plant!

So this is where early flowering varieties come in to the picture. Early, non-automatic strains still require a certain number of hours of complete darkness in order to trigger their flowering hormones. This means you can keep a mother plant alive (under artificial light) in the vegetative state and take cuttings from her year after year. However, instead of beginning flowering in mid to late September, strains like Korengal Kush, Peanut Butter Herijuana, Okanagan Grape and Laughing Lion will begin flowering many weeks sooner and will also ripen in just 49-56 days as opposed to 65 or more days required for many hybrids.

Now here comes my shameless plug: Lucky 13 Seed Company has just released a new strain I’ve been working on for a number of years called “Frostberry”. It’s genetics include Blackberry Kush and Purple Prozac crossed with a super-early flowering mutant Grand Daddy Purple male. It has been a long and slow process of growing this strain outdoors in the north for many years. Each season only the very earliest flowering males and females were bred together. Through the process of careful selection and lots of patience we have finally arrived at a very early flowering pure Indica strain that has been bred specifically for outdoor growers in cold northern climates.

Frostberry from Lucky 13 Seed Company
All new Frostberry from Lucky 13 Seeds. An early flowering Indica with incredible bag appeal and top shelf potency.

This most recent generation of Frostberry began flowering at the end of July and was ready for harvest in early September, an entire month ahead of everything else in our outdoor garden, and well before the cold set in. Frostberry is not an auto-flower, so it can get very big with impressive yields and packs a serious punch in the potency department. It produces massive stacked buds that are a gorgeous lavender colour with a sweet berry aroma. Resin production has been very impressive, giving the buds a nice frosted look very early into blooming. As temperatures cool off it only further enhances her colour and aroma and really brings out that beautiful sticky resin to an extra degree. We just finished germination testing on this batch of beauties and had 100% germination with over 50 randomly selected seeds.

Frostberry flowering pictures
Frostberry at the beginning stages of flowering already showing beautiful colour and impressive bud size

There are some special considerations when growing Frostberry, however. Although she achieves her fullest potential when grown outdoors in full sun, she can certainly be grown indoors as well. If you start seedlings indoors or keep her on artificial light, it is necessary to run your lights for 20 hours on, 4 hours off to keep her from flowering. For this reason, Frostberry is really not recommended for outdoor growers near the equator; the daylight hours are just not long enough to grow her properly in these locations.

Frostberry mold resistant strain
Frostberry at 4 weeks into flowering in August. Still lots of size and resin to come with plenty of warm weather left.

The next thing to consider is her stature and growth habits. She likes to produce tall and super-thick colas with little to no side branching. For this reason you’re going to want to top her frequently early on in her life cycle to get multiple terminal buds and spread her out as much as possible for the best yields. Or you can simply grow her sea-of-green style with multiple plants grown closely together without topping. The latter method will result in faster growth and massive trees by the end of the season with enormous berry-perfumed colas. We’ve used this method on the farm with great success, planting a full 13-seed pack in a single 10 gallon fabric container, and then plucking out the males when they begin to show. And no need to worry about accidental pollination; the males will reveal themselves around two weeks before the females so you’ll have plenty of time to chop them down to avoid seeded buds.

Frostberry cola
Frostberry like to grow tall and thick with virtually no side branching. Top early and often for massive yields.

So if you’re an outdoor grower who, like me, hasn’t been very impressed with auto buds, I think you will be pleasantly surprised by Frostberry. She’s got everything you’d expect in a hard-hitting medicinal Indica while allowing you to achieve an accelerated growth rate and yield in the great outdoors that simply isn’t possible with standard strains. Check out our strains page to order a couple of packs of Frostberry today.

Frostberry cannabis seed
Ripe Frostberry seed bursting through the husk.

Frostberry purple seed
Frostberry's gorgeous purple colouring saturates the entire bud and even the seed pods.

Hint: Want a massive bumper crop next summer? Grow two or three packs of Frostberry indoors over the winter and clone everything during the vegetative growth stage. When you harvest take note of the biggest, baddest, stickiest female from the group and turn that clone into a mother plant. When next May rolls around take as many cuttings from your mother plant as local laws will allow and plant them in the ground in rich, fertile soil and get ready for an insane harvest at the end of Summer.

Happy Gardening!

Professor Sprout

Special Note: This season I was able to obtain a handful of seeds from an old hippie who has been growing a strange mutant sativa strain out in the bush for many generations. His plants routinely finish in the middle of August! This is unheard of for a non-auto and especially so for a non-auto sativa. I'll be running some tests with these genetics next season. I'm very excited about this one as I think it has tremendous breeding potential and could be an absolutely bonkers strain for us northern growers who like a speedy sativa rush. I’ll be sure to keep you posted on that project next season.

Frostberry macro
Organically cultivated Frostberry seeds grow fast due to extreme hybrid vigour

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