What Is Photoperiod Cannabis & How To Grow It Outdoors

PHOTOPERIOD, EXPLAINED

When you come across the words photoperiod, photoperiodic, and photoperiodism, think of the hours of light in a given 24-hour period. Cannabis strains that bloom indoors under the standard 12-12 light-dark cycle do so because they are triggered to flower with a longer dark phase.

Outdoors, most photoperiod strains will transition into flowering as the hours of daylight dip below 15. Thus, a longer flowering period is to be expected. 12-12 is optimal for indoor cultivation. That’s why the flowering-time data on the reverse of most cannabis seed packs reflects bloom periods somewhere between 8–12 weeks. Typically, heavy indicas like Northern Light finish flowering fastest, sativas slowest, and indica-sativa hybrids somewhere in the middle.

Autoflowering cannabis is the exception to the rule. Regardless of the hours of light, autos will start to flower around 30 days post-germination (give or take). In contrast, photoperiod cannabis plants can remain in vegetative growth indefinitely, so long as they receive 18–24 hours of light per day.

CRITICAL FACTORS OF OUTDOOR CULTIVATION

THE CANNABIS LIFE CYCLE

Cannabis is an annual plant. And as a short-day plant, it will not be ready for harvest until autumn. In general, cannabis planted in the spring after the equinox will gradually shift from vegetative growth to bloom some time after the summer solstice, and finally be ready for harvest sometime during autumn. How much sunlight each plant receives will set the pace of the crop.

Greenhouse growers can use tarps and light-proof plastic sheeting to reduce the hours of sunlight and trigger plants to bloom faster. The only downside is it turns the grower into a walking timer plug. Don’t forget to remove the shade material before sunrise.

LOCATION, LOCATION, LOCATION

In the Northern Hemisphere, the outdoor growing season is April–November. The summers become shorter and winters colder the further north you go. In the Southern Hemisphere, it’s the complete opposite, with the season running from August–April. Of course, there will be some regions that are outliers. But unless you are living close to the equator where a near-constant natural 12-12 day and night cycle prevails year-round, you must do some research.

SUNRISE AND SUNSET DATA

Data is digital gold. Use an online sunrise-sunset calculator. You need to study the historic monthly analysis for your local area. This is absolute need-to-know information. The sun is your grow light in the sky. You must be certain of how many hours your plants will receive before you germinate a seed.

First, you must pinpoint when 18+ hours of light will be available for vegetative growth. Then you must check approximately when sunlight is less than 12 hours to estimate a harvest window. Don’t get too hung up on a perfect 12-12. Remember, outdoor photoperiod cannabis will bloom slow and steady as the nights get longer. Some late-blooming super sativas like Amnesia Haze can grow to enormous sizes and not finish flowering until sunlight is down to 11 hours per day in late-autumn.

WEATHER FORECAST

18+ hours of daily sunshine is not enough to get growing. Check the weather forecast regularly and study the historical data for the last few years. Spring in Northern Europe is still pretty cold. For best results, cannabis needs 20–28°C temperatures to grow to its full potential. The reality is if you live too far north of the Mediterranean, you have a very short growing season. A hardy autoflowering hybrid like Blue Cheese Automatic is better suited to cooler northern climates. Lucky continental growers can really go for it with exotic strains like Kali Dog and Chocolate Haze.

SITE INSPECTION

OK, so you have completed your desk research. Now it’s time to do some field research. You must inspect your grow site. Make sure no obstacles are casting shadows to block sunlight, and scout around the area to make sure it’s safe from prying eyes too. The best outdoor grow space is a private one. Use chicken wire and fencing to keep out any weed-munching herbivores or rodents.

GENETICS

You must tailor your choice of cannabis seeds to your microclimate. Use the RQS strain filter to help make this important decision. One of the big advantages all photoperiod strains have over autoflowering cannabis is you can take cuttings to preserve the genetics. When you find a winning mother plant that thrives in your cannabis garden, cut clones to repeat the success.

CLIMATE CHANGE

Climate change is already destroying outdoor cannabis farms. Growers in Northern California saw crops go up in flames in 2017. Smoke from the wildfires tainted marijuana growing for miles around. This is an extreme example, but extreme weather events are a real threat to outdoor cannabis cultivation everywhere. All you can do is be aware of the current weather patterns in your region.

PRO TIPS

Getting started indoors is always a smart idea. If you have good weather, a sunny windowsill is a good spot for delicate seedlings. Or, if it’s still too cold and raining outside, you can use a 200W cool white CFL to see plants through vegetative growth. A hybrid indoor-outdoor grow is not a compromise, it’s getting the best of both worlds.

We recommend growing outdoors using cannabis-specific soils in white plastic pots or Smart Pots. Pick up some brand name dope-growing dirt from the local grow store. You can do little more than staking plants with bamboo for support if you grow in the ground. Containers give you the option of moving plants. This is usually required as the seasons change. The Earth moves around the sun, so if you are growing on a balcony or terrace, you may need to move plants around as the day progresses to keep them in direct sunlight.