How to plant marijuana seeds in winter

The Cannabis plants love warm and sunny locations, but does this mean that you cannot plant marijuana seeds in the winter? Not necessarily: your chances of success will depend on what the winter season is like where you live. Outdoors, low temperatures and lack of light make the process especially difficult, so yields tend to be smaller. Fortunately though, thanks to the advancements in indoor techniques, it is now possible to grow all year round in the comfort of your own home.

In countries closer to the tropics, where temperatures are quite mild even in the winter, it is possible to grow marijuana outdoors all year round. However, at latitudes that are further from the equator, cannabis doesn’t often develop properly outdoors in the winter, especially in snow or freezing conditions. Even though some strains can withstand lower temperatures better than others, warmth is the key if what you’re looking for is high-quality weed.

Once the temperature drops below 15ºC, the metabolism of cannabis plants gradually slows down as their biochemical and enzymatic processes become paralysed. Under these circumstances, their root system doesn’t expand as it should, which means that the plants cannot absorb as many nutrients as usual, which in turn leads to highly unproductive growth.

So ultimately, if you want to plant cannabis seeds in the winter, you need to evaluate the pros and cons of indoor growing versus outdoor growing, and then decide which one better adapts to your needs. Here are some basic tips for successfully planting marijuana seeds in the winter:

1- What cannabis seeds should you plant in winter? Choose the right strain.

Some marijuana strains work better than others in colder climates. Look for indica-dominant varieties from those parts of the world that tend to be cooler, as these have adapted more effectively to the difficulties of living in the open. Sativas originate from tropical regions with warm and humid climates, so they struggle more than the indicas in cold environments.

Our seed catalogue includes several options that are worth considering:

• CRITICAL GENETICS: Kritikal-k
• WIDOW GENETICS: Feminized Silver Widow
• SKUNK GENETICS: Feminized Skunk+
• KUSH GENETICS: Purple Kush, Og Kush

Of all the possible options, autoflowerings are usually the most suitable. Thanks to their ruderalis heritage, which derives from regions like Siberia, these cannabis plants have adapted to adverse climate conditions and to the different day and night durations with minimum resources. As a result, they are more resistant to the cold and don’t depend on the photoperiod to start flowering, which makes them much easier to grow in the winter.

Here are some highly resistant varieties that will definitely solve any doubts about which autoflowering seeds you should plant in winter:

• GINGER ALE GENETICS: Ginger Punch Auto
• CRITICAL GENETICS: Kritic Auto
• XL GENETICS: Amnesia Dream XXL Auto

Indoors: Regardless of the type of seed, the temperature for germination must remain between 22ºC and 25ºC, with a relative humidity between 70% and 90%. These conditions can be difficult to achieve unless you grow indoors or use a mini greenhouse. We recommend keeping your seedlings indoors until their vegetable mass has grown substantially and their root system is extensive enough for them to feed through it.

2- Keep an eye on the root system as it is the one that suffers most from the cold.

The health of the root system is vital when you’re planting seeds in the winter, especially during the seedling phase. When outdoor cannabis is grown in pots, the root area can get very cold. Plants that have rooted directly into the soil cannot be moved, but their roots will stay much warmer than in a pot during a cold night.

Top tip: during the hours of darkness, outdoor plants can be covered with plastic sheets to help them retain the heat. In any case, it’s always best to shelter them in a greenhouse if you have one available.

Indoors: LED lighting can be highly efficient, but HPS technology has a major advantage in winter because it produces a lot of heat. If you have a cold grow room, an HPS light can have a double function as a source of both light and heat for your plants. However, you should always take into consideration the temperature of your grow room when the lights are off.

3- Keep a constant temperature to prevent thermal stress.

The optimum daytime temperature for cannabis is between 24ºC and 29°C, whereas the optimum night temperature ranges between 18ºC and 22°C. It is essential to avoid large contrasts between the two, as a constant temperature helps the plants optimise their growth, health, yield, and potential. In some areas the changes in temperature between night and day can be extreme, so using a greenhouse will help minimise this thermal contrast.

Indoors: If you grow cannabis indoors when it’s cold outside, it’s advisable to start the light cycle after sunset, when the temperature is lower. This way, the darkness cycle occurs during the day, when the temperature is higher, which in turn helps to prevent extreme changes in temperature.

4- Controlling the humidity levels: a double-edged sword.

It’s quite common to be confronted with rainy, frosty, or foggy conditions during the colder months. Besides, morning dew can appear, which creates the perfect environment for the development of mould and fungi. Find an outdoor grow space that gets a lot of sun in the morning and is protected from the prevailing wind. This will help the morning dew evaporate more quickly.

Indoors: Freshly planted marijuana seeds need between 80% and 90% relative humidity to germinate. Humidity is then decreased progressively to 60-70% during the vegetative phase. These parameters can be easily controlled through the use of air conditioning and dehumidifiers. However, indoor humidity is lower in winter than in summer, and in some cases can drop below the optimum range. There are several ways to correct this; for instance, by increasing intraction power so that more humid air comes in from the outside.

5- Be careful with overfeeding: less is always more.

Cold air tends to be drier, and the roots of the cannabis plants can compensate for this by absorbing more water. But this can be problematic if the seedlings grow in a substrate that is particularly rich in nutrients, as it can lead to burns on the tips of the leaves caused by overfeeding. But if the temperature drops too much, down to 10ºC or even lower, then the plants will struggle to absorb the nutrients effectively (especially phosphorus and magnesium). This is what is known as ‘nutrient lockout’.

Indoors: In this case, you must consider using a heating system or maybe some heating blankets to stop the root area from getting too cold. If you’re growing in hydroponic media such as coco coir, remember that with feeding ‘restraint is a virtue’: you can always resort to foliar fertilisation if you’ve fallen short.

As you can see, planting marijuana seeds in the winter doesn’t need to be an odyssey if you follow our advice. With some advance planning you can prevent plant issues and guarantee a successful harvest. We encourage you to check it out for yourself!