10 unexpected problems that may arise in cannabis growing and how to solve them

Although they are rare, there are some unexpected events that can negatively affect the development of your cannabis plants. Therefore, the simple fact of knowing what they are can help you to identify them and possibly avoid them in the future.

The Pareto principle states that 80% of consequences come from 20% of possible causes. But what happens with those rare issues that can occur in cannabis growing? Here we analyse 10 unforeseen complications that may never have happened to you, but that’s not to say that you’ll never have to deal with them in the future.

1- Can a brief light leak during the 12-hour darkness period turn a feminised plant into a male?

Light leaks during the flowering period, however small, can stress the plants and make them react by becoming hermaphrodite (this is when they exhibit both male and female characteristics). This really depends on the genetics of the plant and the duration of the interruption of the dark cycle, so some plants will be affected more than others. If you find sacks of pollen forming on the plants, it’s best to get rid of them and start fresh with new seeds.

2- My seedlings grow to a height of 15 cm or higher, and then their own weight causes them to fall. Could this be happening because I didn’t plant the seeds deep enough, or could it be something else?

The initial diagnosis is that the light is too far from the top of the seedlings, so they need to stretch in search of it before they fall over. Adjust your lamp so that it’s closer to the plants and this issue should disappear completely. If your seedlings are still alive, you can still recover them by carefully taking them out of their container and replanting them, with most of the stem buried in the soil (just up to the first leaves). Some light airflow from a fan can also help strengthen the stems so that they can better withstand the weight of the cotyledons.

3- You buy some seeds and, when they germinate, one of them sprouts twins. Is that a bad thing?

Those plants exhibit a common mutation called polyembryony, an anomaly of two or more embryos developing within the same seed. Just like identical human twins, the seedlings that emerge will be exact copies of each other. You’ll obtain two different roots from a polyembryonic seed, which makes separation harder but not impossible. The seed shell can be removed after germination has ended, and the two shoots can be carefully separated. After the plants have been split, they can be planted normally in two separate pots.

4- You’ve accidentally mixed feminised and autoflowering seeds. Can they be identified by their size?

You won’t be able to tell the difference between autoflowering and feminised seeds from their size, as this is governed by genetics and by the required growing conditions for those seeds. You’ll need to plant and grow them to determine which is which. Those that start flowering, regardless of the amount of light that they’re exposed to, will be autos. The rest will be feminised.

5- You’ve planted two seeds in the same pot to keep the most vigorous one but, at the time of separating them, their roots are tangled together. Should I leave them like that or separate them?

Planting more than one cannabis seed in the same pot is not recommended. The roots get entangled, and the plants must then fight for nutrients and light. This results in significantly lower yields than those of plants that grow separately. Having reached this point, however, it is advisable to not separate them so as to avoid the stress that this would inevitably cause.

6- I place my cuttings in clear plastic glasses with potting soil, but, after a few days, there’s some green moss around the root ball. What is it?

The green mould is algae that grow because the plastic cups are clear, so the light can reach the humid growing medium, creating the perfect conditions for the moss to start competing with the plants for nutrients, as well as creating a breeding ground for harmful pests and moulds. Transplant the cuttings immediately into larger opaque containers with plenty of soil mix.

7- My indoor timer stopped working while I was away on a weekend break, so my plants have spent 3 days in total darkness. Can they somehow recover?

When cannabis plants are subjected to total darkness for several days, they are likely to stretch in search of light, showing signs of premature ageing. However, it is possible to recover them because they’re very hardy and are able to adapt to adverse situations. Nonetheless, once the optimal lighting conditions have been re-established, the stress levels that they’ve been submitted to will translate into lower yields than usual.

8- I follow the directions on my nutrient containers to the letter, but the tips of the leaves always end up getting burnt. What am I doing wrong?

The recommended amounts on the labels of nutrient containers tend to lean towards the maximum that plants can absorb, which can sometimes lead to overfeeding issues. Most fertiliser firms want you to go through your fertilisers as quickly as possible, so you then have to buy more. A good piece of advice is to feed at half the rate recommended by the manufacturer, unless you spot signs of low nutrition. It is best to err on the side of caution than having to deal with the nightmare of recklessness.

9- I’m growing outdoors in a humid climate, but as it’s been raining for several days in a row, my plants are now being eaten by snails and slugs. What’s the best solution?

These invertebrates can be seriously problematic, especially for young plants. Scattering some diatomaceous earth around the plants can be a good idea to get rid of them: when the snails and slugs get coated in diatomaceous earth, its silicic composition causes them to dehydrate and eventually die. Another great remedy is to bury a glass of beer in the ground, leaving the rim at ground level: these gastropods cannot resist the yeast mixture, so they end up falling right in and drowning.

10- My plants exhibit a set of strange symptoms without an obvious cause: stunted growth, brittle stems, scarce flowering, deformity and chlorosis on the leaves… What could be happening to them?

If you’re actually doing things well, a mix of all these symptoms at the same time is usually an indication of a devastating diagnosis: a virus is attacking your cannabis plants. Marijuana is prone to suffer from many viral infections, including the alfalfa mosaic virus (AMV), the cucumber mosaic virus (CMV), the tobacco mosaic virus (TMV), and the hop latent viroid (HLVd). And once any of these attack the cannabis plants, there is no way back.

You have two options: firstly, prevention; and secondly, the detection of infected plants so you can remove them from your grow (these viruses are transmitted through contact). The maintenance of mother plants for cuttings, or the actual exchange of cuttings, are also great catalysts for the spread of these phytoviruses. Therefore, a thorough clean of your grow tent and planting cannabis seeds rather than cuttings will help you increase your chances of avoiding this huge and unexpected issue.