Moving Your Weed Grow Indoors for Winter: Pros, Cons, Night-Time Lights and Humidity

Moving your cannabis grow indoors for winter

Most winters are too cold and too dark for cannabis outdoors, so many growers move indoors after the outdoor harvest and keep going all season. Indoors you control the environment: aim for 20-25 °C (68-77 °F) and never below 18 °C (64 °F), run the lights at night when it's coldest, keep humidity in check to avoid mold, and lean on mold-resistant or autoflowering strains. Growing through the winter is harder to manage, but it's definitely doable.

Winters vary a lot, and obviously some climates are harsher than others. Depending on where you live, you might be able to keep plants outside a little longer into the fall.

Even so, most of the time winter just isn't suitable for cannabis to grow properly outdoors, especially if it snows or temperatures drop below freezing. Some strains can handle slightly lower temperatures, but warmth is key if you're after high-quality bud.

Lots of growers take things indoors once the outdoor plants have been harvested, so they can keep growing through the winter without too much hassle.

It takes some planning and investment, but having an indoor grow room ready for when the cold hits can make a big difference. It also gives you a space to start plants ahead of next year's outdoor season.

Being able to grow through the winter means more harvests a year of your favorite plants. Setting up an indoor grow in the cold months comes with a few extra perks, too. With the right setup, the heat thrown off by your lights and other gear can help warm your home. Your electric bill will probably go up, but the extra buds at the end of the cycle may well make it worth the cost.

Pros of growing indoors in winter:

More harvests per year

Full control over the environment

Lower odds of pests

Cons of growing indoors in winter:

Expensive to set up

Costs electricity

Requires heavy maintenance

Once temperatures drop to 15 °C (59 °F) or lower, growth tends to slow way down. Below freezing, a cannabis plant is likely to die.

Your best bet is to keep the temperature above 18 °C (64 °F) at all times. Somewhere between 20 and 25 °C (68-77 °F) is usually the sweet spot. Bottom line: you need to keep an eye on the temperature to make sure your plants don't get too cold, or they'll suffer.

Watch the dark hours closely, since your lights aren't putting out any heat then. You may need heaters to keep temperatures in the comfortable range. You can put them on timers so they kick on when the lights go off.

It can be a good idea to set your lights to run overnight, when it's coldest outside, and switch them off during the warmer part of the day. That helps you avoid big temperature swings that can stress your plants.

The sun is a cannabis plant's main energy source, and it delivers plenty of light in the summer months. In winter, there just aren't enough daylight hours to meet the plant's needs. That's why you need to add light to make up the difference.

HID lamps are powerful enough to grow weed indoors through the winter and have the bonus of giving off a lot of heat. You can also use LEDs or fluorescents (which are cheaper to run), but plan on extra heating, since they won't give your plants much warmth.

Keeping relative humidity (RH) where it should be can be tricky when it's cold. Humidity often goes up as temperatures drop, so if you're pulling in cold air from outside, RH usually runs high. Depending on the growth stage, try to keep RH in the grow room between 40% and 75%.

High humidity is usually what causes mold, and mold gets harder and harder to control the colder it gets. Dehumidifiers do a good job of bringing RH down, but how well they pull moisture out of the air depends on the size of the space and the quality of the unit.

You can still use natural sunlight in winter. The sun doesn't stick around long, but for a few hours it can be strong enough to give your plants a solid dose of light. Growers who go the greenhouse route can add gear like supplemental lights or install blackout blinds or covers to help manage the light schedule.

When it comes to picking seeds, mold-resistant strains and autoflowers tend to do better in colder conditions. These are usually indica-dominant. Sativas come from hot, humid climates and struggle with the cold more than indicas do.

Thanks to their ruderalis genetics, autoflowers are ideal because they have a short cycle and flower based on age rather than light hours, which makes them much easier to grow in winter. Still, autoflowers need plenty of light in their vegetative stage to reach their full potential.

With all the options available for growing indoors, a winter grow is definitely worth considering. Yields will be better, and you cut down the odds of losing seeds or clones to cold weather and mold. On top of that, you get to experiment with all kinds of indoor techniques that can help you become a better grower.

How do you grow autoflowers in winter?

Growing autoflowers in winter can be a challenge, since these plants have a short life cycle and need good conditions to grow and flower properly. That said, here are a few tips that could help:

1. Pick the right strains: choose autoflowering strains that handle cold well and suit a winter grow. Some autos tolerate the cold better than others, so researching and choosing cold-hardy strains is key.
2. Protect them from the cold: winter temperatures can drop low enough to hurt your plants. Give them protection with things like greenhouses, grow tunnels, frost blankets or extra lights to keep temperatures in the right range for autoflowers.
3. Plan your grow: in winter the days are shorter and daylight hours are limited. So plan your autoflower grow around the light you'll have available to make sure the plants grow and flower properly.
4. Feed them right: in winter, cannabis plants can have different nutrient needs because of the cold and the lower light. Adjust your feeding accordingly, using suitable fertilizers and following the manufacturer's directions.
5. Water carefully: watering is a big deal in a winter grow, since plants may need less water because of the cold and a slower transpiration rate. Adjust watering to each plant's needs and avoid excess moisture, which can lead to mold and disease.
6. Prevent disease: winter conditions can favor plant diseases. Take preventive steps like keeping plants clean, with good airflow and ventilation, and using appropriate products to keep disease from showing up.