Some of the leaves on my plant are getting these dry tips with sort of yellowish spots. What causes this?
It’s root burn, or malabsorption. In short, you’re overfeeding. Ignore these deficiency charts, they only really apply if you’re growing in hydro with de-ionised water as your base for your nutrient solution. Tap water + soil means you have an abundance of all of your micronutrients already. If you’re in a physical media and/or using wholly organic nutrients, you don’t have a deficiency. Nutrient companies release these charts and try to convince you you need to buy a manganese supplement, or a zinc supplement. It’s just nonsense meant to prey on people that don’t have an education in horticulture and it will only make your situation worse. I can tell by looking at the leaf in the back (see the way the colour kinda fades across it?) that it’s not binding nitrogen correctly. The pale colour shift is classic. What I would do, personally, is flush the medium (I’m assuming soil?) with plain water, use approximately 3 times the water in litres as exists in the pot. So, if you’ve got 10 litres of soil in there, pass 30L of water through it. After that, leave it for 2 days to dry out and then add feed again at 1/2 the ratio you’re using. You’re already in flower, so you need to sort out these root problems today, because the root won’t recover the stuff you burn away.
It’s a trap everyone falls into, the plant consumes more in flower so people up their feed. They consume more, but they don’t consume everything that you put in the medium. If you’ve already got a high-level nutrient solution in the soil and you add to it what happens is reverse osmosis, so the water is ripped from the root to equalise the osmotic pressure between nutrient saturated medium and the rootbed, because water moves from an area of high concentration to low concentration across a semi-permeable membrane. Flush it, give it two days, reintroduce nutrients at half the strength. I don’t know how you’re measuring the feed, but general rule is less is more. It’s been ages since I’ve done wholly organic growing, now I use salt solution nutrients in de-ionised water at 20-10-20 N-P-K, starting 550 mols/cm3 and moving to 800 mols/cm3 as you progress from veg into flowering. That is it, that is all the plant needs. If you are using organics, you need to keep your concentrations measured as well. It’s like jam, or salt preservatives you’ll overwhelm the bacteria present at the root base, so they won’t be able to break it down. That will further fuck with your pH and lead to more root damage.
Source: Bachelors in plant sciences, former master grower.
Edit: Just to add, the reason this “looks like deficiencies” is because when you saturate a plant’s root base to the point it causes burn, or malabsorbtion (see “lockout”) it can’t bind any of the essential micronutrients. Rule of thumb, if you’re in soil, not deionising your water. Every “deficiency” is caused by root problems and this is why you need plant scientists and not people who trust what AI tells them about plants.
Well I knew I was coming to the right place for help but sure wasn’t expecting it at this level! Thanks for the thorough analysis. It does seem to have stalled a bit in growth compared to other plants - I suppose that is a symptom of malabsorption too?
No worries buddy, I usually just lurk but I saw someone suggesting AI and I went ‘nope’. Correct, it all comes down to roots. You have 3 types of meristemic tissue, which are you bread and butter for growth. if you like. It’s where undefined cells are sent to gather and form new structures/tissues. The ground mersitem at the roots, the apical meristem at the nodes and the Procambium which is what creates your phloem and xylem, your transport tissue. Undefined cells are produced at the root meristem and then sent to areas of the plant for growth by chemical messengers called auxins. So, if your pH is out, the plant can’t bind essential nutrients and it looks deficient. If you’re oversaturated with salts/fertiliser it damages the root and diminishes the capacity to produce new undefined cells to send to these areas and again, it looks like it’s deficient. It also changes the priority of where they’re distributed, because now they’re also trying to limit damage that’s occurring at the root bed. You’ll notice that it’s the tips that get consumed first, that’s because leaves are energy stores. So, because it isn’t getting the nutrition from the transport tissue, because of root issues, it depletes those stored in the leaves to try and make up for it. That reduces the ability of the plant to photosynthesise, reduces the binding of carbon from Co2 using RuBisCo, which lowers the rate of cellular respiration, damages the ability of the plant to utilise nutrients from the feed and further slows growth. So, it’s like a knock-on effect.
Ah that makes sense! It’s really cool to understand the underlying mechanics.
There’s a University text book you can get really cheap second hand called “Plant Propagation and Practices.” If you read through the sections on the structure of flowering plants, herbaceous plants and olericulture, You will know more about cannabis cultivation than any youtuber, influencer, or cannabis themed company around. The internet is not a good resource, because most of the information is put out by seed companies, nutrient companies and purveyors of cheap grow lights. It’s not all awful, but the fact is they don’t exist to ensure that your plants are great and you produce lots of cannabis with very little effort. They exist to sell you their below commercial quality equipment, at an insane markup, when you can get identical, or better equipment from Alibaba. Advanced Nutrients has made an absolute killing splitting up N-P-K over and over again and selling it back to you at 300% mark up. The mermaid with the big tits on the bottle, isn’t for the plant, it’s for you!
You know I just might order that. I’m so tired of the pitch and all the SEO garbage and that’s before the AI slop started to take over. Makes learning about something such a hassle.
Is this the one?
https://archive.org/details/PlantPropagationPrinciplesAndPacticesByHartmannAndKesters8thEdition
Probably close enough. This is the guy I used in college though. Anything from 5th edition up and you should be golden. Biology doesn’t really change that much, Universities just like to recharge you for the same information. I completely agree with you on the AI slop. I use a flip phone and a library card. Any dumb-dumb can get ChatGPT to create an article online to sell you something. University text books are dense and boring and the only place I would look if I wanted to learn a completely new skill. Good luck with the babies bro!
Also, sorry, just to add. Over-watering, having the medium wet all the time. Will massively reduce growth. You want Co2 at the leaves and oxygen at the roots. If it’s wet all the time it just won’t grow, you gotta let them dry out between fertigating. Pick up the pot, if it feels light, water it.
No apologies at all, I appreciate all the help. So lots of light and a bit of dry time between waterings is best, right?
Simplicity is everything. Light is a different school of thought. For indoor growing if you’re not adding Co2 a PAR of around 800 is sufficient, if you’re using a PAR meter. You can get away with a Lux meter (30 euro about) with a reading of about 70,000 if you’re using white LED’s, so, full spectrum grow lights. For the blue-purple LEDs you have to use a PAR meter. Which is substantially more expensive than a lux meter, but you can get a cheap one for a couple hundred euros. If you’re not at the stage where you want to buy a meter to measure the light. Just keep it at a distance so the plant doesn’t bleach. That’s the breakdown of chlorophyll which is the green pigment responsible for photosynthesis. If it’s natural light, just leave it be.
This may help
Zinc deficiency?
Charts like this are quite useless in my view. They confuse more than they help. The issue is almost always either watering or PH. If not, then it’s overfeeding (clawing/burnt leaf tips) or underfeeding (yellowing leaves on the bottom of the plant) the only exception to this is cal/mag deficiency which is easy to diagnose by mixing a foliage spray and misting both sides of the leaves. It should respond in few days given you’ve addressed potential watering/PH issues first.
Thanks! I’ll keep this around.
Can you show more of the plant?
Are you sure those no parasites?
Yeah fairly sure no parasites. The rest of the plant looks pretty normal outside of a couple leaves that look like that
FWIW, various LLMs seem to think this is caused by nutrient imbalance, specifically potassium deficiency. That potassium deficiency can also be a knock-on effect from overdoing it on calcium or magnesium affecting potassium uptake. Finally, another thing to consider is pH testing the soil. If you’re using a nutrient mix, you might need to flush the soil and start over (especially if you over did it). If you’re not using a nutrient mix, you should consider doing that.
Could be zinc, it potassium deficiency, also how big is your pot? Are the roots getting crowded? May need to repot. Also could be too close to the light
Also, if you’re growing in dirt, look into getting a 5 gallon bucket hydroponic setup. Super cheap and easy, just make sure your pump stays going 24/7
Definitely thought about hydro but haven’t had the time yet! Thanks for the suggestions, I’ll look into them.