Growing cannabis outdoors involves sunlight, and having plants exposed to intense sunlight can spell trouble. If your plants face the kind of scorching heat that summer often brings, it can cause them (and you) stress, affecting growth and overall health. Fortunately, there are ways to protect your plants from heat damage. Seedsman recommends the best ones.
An outdoor cannabis grow is more challenging to control than indoor growing. Indoor growers can take complete control of their climate and use equipment and timers to ensure a perfect environment, but outdoor growing is very much at the mercy of nature. Knowing how to compensate for elemental variables is vital to protecting your cannabis through its lifecycle, with shelter among the primary concerns. Be proactive rather than reactive here, and stack the odds in your favour.
How Heat Stress Affects Cannabis Plants
Heat stress is just one of several real enemies outdoor growers face. Whether you grow photoperiod plants or autoflower strains, you must guard against the sun. The damage it can cause to your plants ranges from bad to severe depending on how intense the heat is and how long your plants are exposed to it. The spectrum of damage heat can cause is wide, ranging from drooping or wilting leaves to stunted plant growth. Know the signs of heat stress, and this will give you a clearer path to a remedy. As with any plant problem, once you see signs of damage, act fast to arrest it.
What Are The Signs Of Heat Stress?
Heat stress manifests differently based on your plant's life stage. Common symptoms that display in each cycle are as follows:
Seedling Stage: Slow or stunted growth indicates that your seedlings are struggling, but to narrow down the cause, pale and withered leaves are a sign of heat stress at this stage.
Vegetative Stage: One of the earliest and surest signs of heat stress in vegetating cannabis plants is when the fan leaves curl upward. Some people describe it as the leaf begins to fold in and take on a taco-like appearance. Leaves will also look withered, crispy, and dry and exhibit odd-shaped brown spots or patches.
Flowering Stage: Be on the lookout for yellowing on the upper and outer areas of the plant. These areas receive the most sunlight and are often among the first to display warning signs. During the flowering phase, your cannabis plants may offer a different character of heat stress - a condition known as foxtailing. This manifests as new buds growing out of the tops of old ones and is a survival mechanism of the cannabis plant as it seeks to remain viable for reproduction in the face of heat stress. Your plants will put out these buds on top, which are airy and without much substance, as it abandons what it sees as ailing buds and tries to start anew.
Among the worst side-effects of heat stress is that your plant may opt to cease growing entirely, leaving you with either a failed crop or a severely diminished yield at harvest time.
What Causes Heat Stress?
It’s not only the sun that causes heat stress – other contributing factors may potentially do the damage, such as:
Low Humidity: Making it difficult for the plant to keep cool
Too Much Light: Apparent through signs of bleaching on the leaves of your plant
Poor Ventilation: Plants don’t receive proper air circulation and can’t cool down
These are all associated with high temperatures and will cause varying types and degrees of your damage. Guarding against all of these is necessary to ensure a successful grow. The need will vary based on your climate.
How To Protect Your Plants From The Sun
Genetics
As always, the first layer of protection in cannabis cultivation should start with genetics. If you’re a cannabis grower in a part of the world that experiences scorching heat during growing season, opt for genetics that can handle the hot climate. Heat-resistant cannabis strains do exist, and choosing these for your grow will give you a leg up on beating the burn. Some breeders have intentionally created cultivars to resist high temperatures, and buying these cannabis seeds is the wisest choice to limit your troubles.
Look to sativas and sativa-dominant strains in particular, rather than indicas, to combat the intense summer heat. These varieties typically evolved in hotter climates to cope with the sun’s fiery rays. Strains such as Amnesia Haze, Mama Thai,Sugar Haze and Lemonchello Haze all have the solid genetics needed to thrive in hot temperatures – but don’t let this make you complacent. Remain diligent and check plants regularly for signs of damage, regardless of their genetics.
Planting
Where and how you situate your plants outdoors is another factor in protecting them from the sun. It’s worth considering growing in pots to re-situate your plants in a more favourable spot if a heatwave should strike. Don’t be tempted to stick them in the shade all day, however, as a lack of direct sunlight is detrimental to vital photosynthesis and the production of cannabinoids like that all-important THC.
Pots
Choosing the right pots for your climate can make a difference in protecting from heat damage to the roots. Fabric pots will allow your roots to breathe, letting air in through the sides of the pots and also helping drainage. Just remember that fabric pots will dry out more quickly, so adjust your watering practices to compensate.
Watering
Who doesn’t like a cool refreshing drink on a hot day, right? Plants are no different. Plants drink a lot in the heat, so make sure the growing medium never dries out completely on those hottest days. Protecting your plants from the sun involves several facets, one of which is ensuring adequate hydration to those roots. Just be careful not to overwater your plants, as that can do different damage.
Timing your watering is also important when guarding against sun damage. Aim to water your plants in the early morning or evening to lower the risk of harm to your plants – water droplets can essentially act as a magnifying glass for the sun’s rays, increasing heat damage to plant tissue.
Avoid soaking your growing medium every day, or else you’ll starve the roots of oxygen, but do ensure your roots have plenty of drainage. You can employ a layer of mulch on your topsoil to keep your things moist for longer in the heat.
Shelter
Elegant ladies used to carry a parasol to provide temporary shade from the sun’s heat, and your elegant ladies will benefit from something similar! Crafting a temporary shelter to pull over your plants during the hottest hours will provide them with a necessary layer of protection. Just be careful not to keep them in there too long, or they’ll miss out on the vital sunlight they need to grow and bloom.
A temporary shelter is relatively easy to construct; you only need corner supports, mesh, cloth, or tarpaulin. Pull it over (but not directly on top of) your plants for a couple of hours during the hottest period of the day, then remove it after this period to allow your plants access to those necessary (but less powerful) rays for the remainder of their daily light schedule.
As always, do your preparations in advance. Know the tendencies of your climate and plan accordingly. Start with the rights, keep an eye on substrate moisture levels, and if blazing heat is expected, think about providing shelter for your plants. These tips will keep your plants cool at the root, and stop them from overheating on top.
