Growing cannabis outdoors is an experience that all members of society should endure at once in their life. Watching a seed turn into a young plant and then thrive into a flower-producing gem is just awesome. Unfortunately, there are certain things that growers must combat to get their crop through until harvest without any issues. Below is better explained how to fight heat stress and to avoid any stress or damage to your plant.
By Stoney Tark
Shading and Cover
At first, this may sound like it is counterproductive, depriving the plants of the precious rays of sunshine. Cannabis plants prefer temperatures of 24 degrees Celsius and a comfortable nighttime temperature of a 5-8 degree drop. Temperatures in Southern Europe can exceed 35+ with hot winds blowing. It can be challenging to cool down the air and the plants, which can lead to the water levels in the medium rapidly drying out and running the risk of the plant becoming tired and overtranspiring. A good idea here is to keep the canopy covered with a light sheet netting during the hottest parts of the day. This usually is around 2-3pm and during June, July and August, it will pay well to have had your garden covered. The netting that you will use can shade the plants and reduce the light intensity and drive the temperatures down. Your garden will thank you for it in the long run and will not find these 3 hours of each day to be stressful. Setting up a net can be as easy as attaching four corners of a large mosquito net over your plants from above to 4 pieces of bamboo and fixing in a high up place. This reduction in shade allows the plants to grow in much more comfortable temperatures with a more cooling wind.
This is relevant for a small-scale garden and large-scale farming. Many growers with plants growing in peak time sunshine will feed during the hottest parts of the day, yet with some caution to the effect that foliar spraying can have when in direct sunlight. This method of watering is not as effective as switching your watering times to late morning and early evenings. The reason why watering in smaller quantities during these parts of the day is recommended is that the plant will not transpire as quickly, meaning that they will have a much better opportunity to hold water in the medium and in the plants. In the evenings, the temperatures outside will be far more cooling and will retain the water. During the hottest part of the day, you will want to have your plants in some shade. This is the point in the day where you can encourage dry zones in the growing medium. Allowing the medium to dry and air out to the point of a lightweight pot will flush the substrate you are growing in with nutrient solution and cause air displacement as it exits the base of the pots. Feeding your plants half as much twice as often is an excellent way to expand your root base and reduce stress from excess transpiration from the tissue of the leaves during the hottest parts of the day.
Improving The Growing Medium
An excellent way to retain more moisture in your growing medium over the long term and reducing water usage is to improve your growing medium. This does not mean that you will think of the micro or macronutrients, but more of capillary action and water retention. Growing with a dense soil base can sometimes lead to efficiency issues with regards to the wicking action and water storage. Using coco from the hairs of coconut husks is a brilliant way to retain moisture. Coco has an incredible ability to keep water locked into the substrate, available for the plants to use. Many hydroponic growers who use coco will often mix a 50/50 ratio of coco and perlite as this combination improves drainage, water retention, and capillary action. Adding vermiculite is also a great way to keep the growing medium moist. Vermiculite is a hydrous phyllosilicate mineral that is made when the mineral is heated. A good ratio to mix with an existing soil bed would be a 50/50 ratio and the same with coco to the soil.
Things Not To Do!
Many things will cause the plants more harm than good, and below are listed what some of those are. Never foliar spray the plants when they are in direct sunlight during hot days, in an attempt to cool them down. The only effect this will have will be momentarily and will do more damage over time than benefit. Especially if using a nutrient solution to foliar spray the plants, as this will cause burning of the leaf tissue and permanent damage. Avoid using icy water when feeding the plants, when the temperatures are so hot. We know that all you want to do is cool them down but using really cold water can cause the root zone to shock and the microbiology within the growing medium to have problems. Do not keep the bottoms of the pots you are growing directly on the floor. If you are growing on a terrace, then make sure you elevate the pots onto a wooden pallet. A hot floor will quickly heat up the pots and cause the moisture in the medium to be sucked dry. Hot air circulating the pots will not generate as much stress as a heated plastic container. Overwatering your plants can be a bad habit and, during peak sunshine, the temptation to add more water during feeding times is unbearable. You should consider that less is more and it will only cause the wilting of your plants. Doing this consistently can lead to deficiency problems as the roots try and balance out the plant requirements.