Article written by
Dipak HemrajHead of Research and Education
Content reviewed by
Dr. Lewis JasseyMedical Director - Pediatric Medicine
Table of contents
“Why is my cannabis plant dying?” If this is a question you want an answer to, you’re in the right place.
The most important thing when it comes to saving a dying cannabis plant is to find out what’s wrong. The most common issue is with the growing environment. Are you watering the plants appropriately? Is the lighting adequate? Is it too hot or too cold? Too humid? Ensuring that your cannabis plant is growing in its ideal environment is the best way to get healthy plants, and to find out what’s wrong with your plant/s.
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What are the ideal conditions for a cannabis plant?
These are the main variables to look at when growing healthy cannabis, which can have the added benefit of reviving a sick plant.
For cuttings and seedlings, 68 – 77℉ (20 – 25℃). For flowering plants, up to 83℉ (approx 28℃) and no lower than 64℉ (approx 18℃, usually night time temperatures) is ideal.
During the vegetative stage, a relative humidity of between 40% and 70% is ideal. During the flowering stage, you will want to reduce the humidity in order to prevent bud rot, so the ideal relative humidity is between 40% and 50%.
For cannabis plants in the vegetative stage, up to 18 hours of light per day at a wattage of around 125 watts is ideal. During the flowering stage, higher wattages are needed, with many people starting at around 400 – 600 watts. The higher the wattage, the higher the yields.
However, a plant that is working extra hard is more susceptible to deficiencies and other problems, and light can create heat as well. This means it is important to keep your plant at a reasonable distance away from your light source as well as to cool the plant down or shade it if the grow room or area is getting stressed from too much light and/or heat.
Soil for cannabis plants should be slightly acidic and have a pH of 6.5. Soil has plenty of nutrients, so you do not need to top it up too much, making it a simple and approachable growing medium. However, due to dirt and the potential of pests, some opt for a medium like coco coir and add their own nutrients. However, you still have to look out for fungus and fungus gnats. Coco coir also makes for an excellent mulch for soil, adding nutrients back into your growing medium.
Overfeeding your plant is a common problem. When your plant can’t take up the nutrients that you provide, salts and minerals will accumulate in the growing medium (e.g. soil) over time, making the soil even more acidic. This means that the plant’s roots won’t be able to take up any more nutrients. This is called “nutrient burn”. In such instances, you will need to “flush” the plant’s growing medium.
“Flushing” is where you use pH-balanced water (pH 7.0) to water your plants in order to get rid of any excess salts and nutrients in the growing medium. To flush your plants, drench the growing medium with water numerous times. It should be ample enough that liquid comes out from the bottom of the container each time. Once your plant is flushed, you can feed it nutrients again (unless it’s a week from harvest, when you should avoid adding more nutrients).
Avoid too much water during the seedling and sap phase. Once the plant is in its vegetative stage, it can handle more water. You should drench the growing medium in water, and it should dry out in 2 – 3 days.
If it takes longer, you are either over-watering or the growing medium doesn’t have good drainage, and you should loosen it up. If the growing medium dries out too quickly, the plant is not being watered enough.
You should water every 2 – 3 days. The key to good soil for cannabis plants is to balance moisture retention with water drainage. Generally speaking, it is better to under-water than to overwater your soil, as you can always add, but cannot detract. Overwatering can also wash away essential nutrients.
Ensure that excess water is drained properly. Containers should be lifted slightly off the ground so that all the water can drain and your plants aren’t sitting in stale liquid.
Check out our post, ‘How Do I Keep Cannabis Plants Healthy?’ for more detailed information on nutrients and the ideal conditions.
Keeping pests away from your cannabis crop
We would recommend avoiding pesticides wherever possible, and encourage natural methods of pest control. Ladybugs, frogs, slow worms and other natural predators can get rid of ants, aphids and many other common pests. Strategically-placed adhesives strips can also help treat pests like leaf miners and white flies. Nets and barriers can prevent many birds and mammals from ruining your crops. Scarecrows and other distractions can also help!
Natural and gentler insecticides such as neem oil, spinosad (an insecticide based on chemical compounds found in the bacterial species Saccharopolyspora spinosa), castor oil, garlic- and pepper-infused water, potassium soap, and alcohol-water mixtures will get rid of most bugs that tend to attack cannabis plants, like red spider mites, cochineals and thrips.
Practising crop rotation is generally good practise for the health of your garden, and has the added advantage of ensuring pests don’t colonize particular areas and get used to a food source (i.e. your cannabis plants) being readily available.
Download Free Guide to Plant Pests
Topping and pruning
Topping is when the grower cuts off the main stalk of a cannabis plant during the first few weeks of its vegetative stage in order to force it to grow sideways and bushy. Left untopped, a cannabis plant will usually focus on growing its central stalk and one main cola. A topped plant will redistribute growth hormones from the main stalk to the side stalks, meaning that the grower will get multiple colas rather than just one central one. Not all cannabis varieties can tolerate topping, but topping hardy hybrids like Blue Dream, OG Kush and Skunk #1 may help keep your plant healthy and improve yield.
Pruning is the process of getting rid of old and dead leaves and branches that don’t get much light. Getting rid of old leaves and getting the plant to focus on bud production rather than leaf production is a great way to keep your plants healthy and improve yield. If you have yellowing and dead leaves, cut them off! Removing large branches at the bottom of your plant is a good start. You will want to do most of your pruning during the vegetative period in order to prevent the plant from getting stressed during the flowering period.
Don’t keep your plants in the same pots. When they grow, move them to larger pots. Let the roots flourish and grow and take up lots of the soil.
Knowing when to get rid of weak and dying plants
If your plant is too far gone, don’t hesitate to get rid of them. If there are too many pests, remove the plant from your garden before they infect other plants. If the roots are weak and the plant stunted in growth, get rid of it earlier rather than later. Focus your energies on growing a few high-quality plants rather than lots of plants of varying quality. High-quality females can also be made into mother plants from which you can take clones, so ultimately your future yields will be much greater.
Supplements – fungi, compost teas, silica and seaweed
Mycorrhizal fungi are fungi that colonize and attach themselves to the root of the cannabis plant, establishing a symbiotic relationship and helping the plant take up nutrients in the soil. These fungi can also help protect against pests and diseases, and are one of the best ways to keep plants healthy and to save them from dying an early death.
Compost tea is where compost is steeped in water, passing along all the compost’s nutrients, microorganisms and humates, which help plants better use nutrients already in the soil.
Silica is great for both soil and hydroponic grows, and can increase the plant’s cell wall strength, improve nutrient uptake, protect plants from contaminants, help ward off diseases & pests, and enhance plant metabolism. You can add silica to your soil or spray, but avoid applying it at the same time as you feed your plant.
Seaweed is essentially a fertilizer, giving your plants a massive nutrition boost. However, seaweed can also improve and regulate soil quality, improve stress tolerance, and defend against harmful diseases and pests.
Download Free Guide to Plant Nutrients
Some final tips
Essentially, the key to saving a dying cannabis plant is to keep it in as stress-free an environment as possible. Not too hot or cold, not too much moisture in the air, the appropriate amount of light, and not too much or too little water. Prevention is better than cure, but in the case of cannabis plants, the prevention methods can double-up as cures.
The other key is to learn when to focus your energies on a specific plant. Many people want to keep all the females they can get, but this is not always the best idea. Keeping weak females can just waste valuable time and space, and their susceptibility to pests and diseases may end up infecting other plants. It can feel counterintuitive (and even brutal) at first, but growing strong plants will save on time and effort, and will ultimately improve your yield.
There’s certainly a learning curve when it comes to growing cannabis, and it can require patience and persistence. However, it doesn’t necessarily need to be too difficult, either, and for the average, everyday homegrower, keeping your grow as simple and straightforward as possible will reduce both your stress and the plant’s. Keep to growing solid, well-established cannabis varieties and not trying to go too big with your garden is probably one of the best ways to prevent your plants from dying.
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