The heat of the summer is great news for outdoor cannabis plants – all that wonderful warmth and sunshine fuels healthy growth. However, the height of summer brings its own problems and one issue that can cause anxiety for greenhouse and polytunnel grower concerns watering cannabis plants.
With high summer temperatures, it is essential to establish a disciplined regime for watering
cannabis plants – especially if they are in pots – to ensure they don’t dry out. This is especially important as the marijuana plant moves towards the flowering stage when it needs higher levels of water to make the transition.
How to Provide Moisture For Greenhouse Cannabis Plants
Greenhouses and polytunnels are the gardener’s best friend when outside weather conditions aren’t ideal for growing as they extend the season. However, in the heat of the summer these growing environments can cause problems for cannabis plant watering. This is because the intensity of the temperature can rapidly wick away moisture, especially when cannabis plants are in pots. Dramatic changes in temperature will have a negative effect on your plants and causes stress which may affect plant growth.
There are some simple habits to get into, which can add to the effectiveness of watering cannabis plants in greenhouses and polytunnels. ‘Damping down’ the internal surfaces and floor space in the early morning with a hose pipe (or via a water sprinkler which attaches at the end) will create a moisture base which will provide some humidity as it evaporates. The old gardener’s trick of placing buckets of water inside the greenhouse, to add to the humidity as the day heats up, may also help too depending on your surface area.
Leaving doors and windows will help with cooling and improving shade and ventilation capabilities are another way of preventing moisture loss after watering cannabis plants. If the polytunnel or greenhouse has no natural cover (from trees for example) then consider using gardener’s shade cloth, which will help to reduce the stress caused by heat damage which can adversely affect cannabis plants – causing issues from dried out roots to leaf damage.
Remember that hot air will rise and so ideally your structure will have vents to let it escape. Most greenhouses have this option and you can buy top vents for polytunnels which are easily fitted by cutting a hole in the plastic sheeting. Polytunnels usually have doors at both ends but side vents are also a good idea if the structure is longer than 10 meters, in order to prevent a build up of stale air in the middle. If the option is available, bringing in a small fan to keep that hot air moving will also pay dividends.
Use Pots!
While plants in the ground will inevitably grow bigger, planting in pots gives the greenhouse gardener much more control. The great thing about growing in pots – so long as they’re not too big and heavy - is that they can be pulled outside to escape the ravages of the hottest part of the day – under some shade and accessing soft breezes.
Of course, this sort of management can be time consuming – especially if the grower is away for the day. For this reason, collection mats buy some extra time between watering and a good tip is to fill a container 10 - 15% over what it can contain with the extra water running off onto a collection mat.
Useful Tips for Growing Cannabis in Pots in Greenhouses and Polytunnels
It goes without saying that larger plants need more water than smaller plants and this is also relevant for different pot sizes, especially if you have a soil mix designed for good drainage ie with perlite and coco husk added to the medium. With this in mind, during the summer over watering is rarely an issue with bigger plants.
It pays to choose the color of your pot wisely – especially in hotter climates, as black and dark colored pots will inevitably absorb more heat and add to the problem of soil drying out. It also pays to be observant of what the weather is doing. For example many gardeners underestimate the effect of wind on drying out plants and soil, which can cause potted cannabis plants to use as much as 2 - 4 times more water than under normal conditions.
In the summer, even the most experienced greenhouse and polytunnel cannabis plant grower can get caught out by the heat – especially on those days that start off overcast and then become blazing hot as the cloud cover melts away. Take some time to prepare however and those cannabis plants will have all the fun in the sun without any of the stress!