Ask the expert: topping, light leakage, curved leaves, and much more

Welcome to our special ‘Ask the expert’ post, where every month we immerse ourselves in the fascinating world of cannabis through your questions, to clear doubts, destroy the myths surrounding erroneous beliefs, and offer practical advice that will help you better understand and take advantage of the qualities of this plant.

On this occasion, we have selected a series of enquiries, made during April through our ‘Ask the expert’ section, which reflect the most common concerns among our readers. From how to identify different marijuana strains to top growing tips, as well as the legal implications of cannabis use. Our aim is to provide you with reliable and up-to-date information that will allow you to make informed decisions and enjoy self-cultivation safely and responsibly. Join us, send us your questions, and discover everything you need to know about cannabis!

Can I legally have any plants at home if this doesn’t bother anyone around me? (Wizza)

The legality surrounding cannabis self-cultivation varies depending on the country where you live and its current legislation. In Spain, for instance, cultivation for personal use is not criminally sanctioned, but beware: this doesn’t mean it is legal. Basically, if you grow marijuana for self-consumption in your home, you cannot be penalised at criminal level, but you can be given an administrative fine. And there isn’t a set number of plants that you can grow: the key is that the plants are for personal use and aren’t placed in visible areas like a terrace or a rooftop. If the number of plants is proven to be for commercialisation, distribution, or trafficking purposes, then the offence can go from administrative to criminal, as it will be considered an offence against public health. In other countries like France, growing cannabis remains illegal, even if it is intended for personal use. French laws are quite strict on this and can result in significant penalties. And at the other end of the scale is Germany, where, as of 1^st April this year, it is legal to grow up to three marijuana plants, provided that it is intended for personal consumption and the plants aren’t a nuisance to neighbours, both in terms of size and the odour that they produce.

Greetings from Canada. I have a few freebies from your collection of genetics. I have Kritikal K and there’s no indication as to whether she’s feminised or autoflowering. According to my research, I’m guessing she’s feminised. Is that right? (Austin)

That’s right, Kritikal K is our photo-dependent feminised version of the legendary Critical + (or Critical Mass). If you’re looking for an auto version of this gem, you should get hold of our Kritic Auto, which is ready in just 70 days from germination to harvest.

Is it possible to identify a strain just by looking at the seed or seedling? My plants got mixed up when I was germinating them (one Mataró Blue and a Super OG Kush). I guess I should be able to tell them apart when they start flowering, but then I’d lose the magic of knowing what I’m growing right now. (Lucas Ezequiel)

Identifying a marijuana variety just by the appearance of the seed or seedling is extremely difficult. Cannabis seeds don’t exhibit any significant visible differences that can be used to distinguish between strains like Mataró Blue and Super OG Kush; and neither do the seedlings, especially when they have the same dominance (indica in this case). The distinction between strains generally starts to become more evident as the plants flower, when you can clearly notice differences in aroma, plant structure, and bud shape and colour.

Can autoflowerings be topped? (Wizza)

Yes, healthy autoflowering plants can respond well to topping providing they have at least 4 or 5 sets of leaves and they still haven’t started producing buds. The best time is usually around the end of week 3; but be careful, since this will cause some degree of stress to the plants. If you grow photo-dependent varieties, you can compensate for this stress by prolonging the vegetative cycle, giving the plant more time to fully recover before it starts flowering. With autoflowering strains, you can’t afford to extend the vegetative phase, and some auto varieties may simply not be able to fully recover from stress, which will therefore lead to lighter and lower quality crops. This is the reason why many growers prefer not to risk it and tend to stay away from techniques like topping.

Hi, I’d like to ask a question about the Break Up Cake Auto seeds that I am currently growing. In practice, how many weeks from germination do they take to be ready? Today I’m starting week 7 overall, and it really doesn’t look like they’ll be ready in 10 weeks. Thank you! (Mark)

Autoflowering plants develop automatically according to their own schedule, and seed banks usually offer an average time (in this case of 10 weeks) as a guideline. However, there’s a certain flexibility in the times. Some phenotypes may take a little longer to be ready, depending on the different growing conditions in which they are being grown.

Can a brief light leakage during the 12-hour period of darkness make a plant grown from a feminised seed become male? (Jorge G.)

Light leaks during the flowering period can impact the plant and make it react, turning it hermaphrodite (i.e. a plant that exhibits both male and female characteristics). This really depends on the plant’s genetics and on the duration of the interruption of the darkness cycle. Growing hermaphrodite plants will result in a harvest of seed-laden flowers, which would be a most unfortunate and horrendous result.

How long does it usually take for the buds to start forming after the 12/12 day/night light cycle has been started? (Pablo)

You should start seeing small flowers forming within a week or two after switching from the vegetative to the flowering phase. Some sativas that have a longer flowering period may take up to three weeks, or even a month, to start producing flowers, but most hybrids available today will show buds sooner. Female pre-flowers look like small balloons with white hairs pointing upwards. In contrast, male plants develop small clusters of ‘bananas’ (or ‘nanners’) that point downwards.

What would be a better option, adding some side lighting to my grow tent or removing the lower branches? I’m not a big supporter of removing anything apart from the fan leaves. I’d like to add LED bars on each side to provide more light to the lower branches. What do you reckon? (Francisco T.)

We recommend adding side lighting instead of removing the lower branches. This will significantly increase the yielding potential at a fairly low cost and with minimum added heat. If you choose not to add side lighting, removing some of the lower branches will send more energy to the upper branches; but, in our opinion, providing more light to the lower branches is a better option.

No matter what I do, the tips of the leaves always get burnt! I am following the instructions on my nutrient containers to the letter, but I always have the same problem. Why could this be? (KarmaKush)

You’re overfeeding your plants. The recommended amounts listed on the labels of nutrient containers tend to lean towards the maximum that plants can absorb, which can sometimes cause slight overfeeding problems. Our advice is to feed at half the recommended dose unless you see clear signs of insufficient feeding. It is easier to fix a nutrient deficiency than for your plants to recover from excessive fertilisation.

Can you tell me why the leaves of my plants, grown in pots indoors, curve downwards? (Yannick)

There are several factors that may be causing your leaves to curve downwards, but the most likely cause is water stress caused by over-watering your plants. Other possibilities include over-fertilisation, high temperatures, or nutrient blockage caused by pH variation. Check the temperature, nutrient, and pH levels: if all of them are within the right parameters, then water stress will likely be the culprit. Let the substrate dry between waterings and the symptoms should go away. It’s also worth mentioning that there are certain plant viruses that cause the leaves to curl downwards, such as Hop Latent Viroid. If you want to learn more about this pathogen, you can check this post.

Remember that you can send all your questions about cannabis to ‘Ask the expert’. Every month we will publish a selection of your queries on our blog, resolving the most outstanding questions.