Greenhouse Cannabis Growing in Winter

Rambo November 15, 2016 Comments Off on Greenhouse Cannabis Growing in Winter
Greenhouse Cannabis Growing in Winter

Q:

I usually grow the normal outdoor season but I have a large 3000 sq/ft greenhouse and I’m thinking of experimenting with a winter crop. I live on the West Coast of the US so December only provides about nine hours of sunlight. Without supplementing light, what effect will the limited daylight have on my harvest?

A:

The short answer… If you fail to provide supplemental light for your winter grow, it’s going to have a huge effect on your harvest. In fact, it will likely make your grow a complete disaster.

Cannabis plants begin to flower in the mid summer as the daylight hours begin to wane. As fall approaches the decreasing sunlight brings the cannabis to full maturity. You need to provide your plants with enough hours of light to keep them in this vegetative state so they will continue to grow instead of beginning to flower right away. Yes a 6 inch plant can flower. Think sea of green. Once the plants do begin to flower, you are going to need enough light intensity so the plants stay healthy and develop nice dense buds.

This being said, if you are willing to pony up for supplemental lighting, I love the idea of growing cannabis in the winter months and making the most of your outdoor/greenhouse growing space. I have explored the feasibility many times. Under the right conditions you can be very successful. Here are a few of my concerns.

  • Supplemental lighting will be needed to extend the daylight hours during veg and ideally during flowering as well. Supplemental lighting is expensive. Both the cost of the equipment and the energy to run it. You probably won’t be able to get away with just enough light to make it “not dark”. In the winter months the sun is low in the sky so the sunlight passes through more atmosphere exposing your plants to fewer lumens. You’ll need to provide enough supplemental lumens so the plants stay healthy and grow. This extra light could could attract unwanted attention.
  • Supplemental light will help but it’s unlikely that your plants will get nearly as large as in the summer. For a winter crop to fill a greenhouse of this size your plant count may expose you to legal concerns.
  • Low overnight temperature could stunt growth. Use of the greenhouse will help but you may still require additional heating which can get expensive.
  • Greenhouses can create insect problems as they provide a more favorable condition than normal outdoor conditions.
  • High humidity caused by winter weather can create fungal problems during flowering which can destroy an entire harvest.

Low soil temperatures often lead to phosphorus uptake problems and if you have a high water table you’ll have even bigger problems from root rot. This will likely require purchasing containers like smart pots and the soil and amendments to fill them.

Beyond the above and the inevitable unforeseen minor issues, I think a winter harvest is a great idea. I live in California and in recent years our winter months feel more like spring… but with shorter days. If you have also been experiencing mild winters, I see no reason why your greenhouse winter harvest would not work. The big issue here is going to be the additional cost of changing your greenhouse to run this type of grow cycle.

Your winter grow is going to look very much like a deprivation (dep.) crop. So I see rows of 3 foot tall plants in something like 15-20 gallon smart pots. The plant count will get totally out of control and could climb as high as 600 or beyond to fill the described structure. Larger plants could be achieved with additional veg time, but I’m not sure if there is time for that.

Depending on when you start your plants for the normal outdoor season, you’ll need to be careful that your winter crop doesn’t overlap and delay your spring planting. Starting your summer crop late could impact the yield more than what you would harvest in the winter. Even after the winter crop is harvested, some time may be needed to prepare the space for the next planting. Additional steps should be taken to remove any lingering pest and fungus fostered by the winter crop to prevent infection of the spring planting.

On the topic of overlapping planting, it’s possible that plant counts from winter crop could overlap with spring planting which could create some very uncomfortable plant counts. Even if this is not a legal issue it could present a labor issue.

To recap, I think a winter crop will come off very much like a dep. We often call these crops “no-pull-deps” because they are so early in the season that blackout plastic is not needed to decrease the hours of light. In my area No-pulls are not uncommon but harvest is generally scheduled around march and very early strains are selected. Strain selection is critical for success for these plantings.

Best of luck, and we would love to hear how this works out for you

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