I stumbled upon a study today while conducting some research on a different topic. I was wondering what the general opinion is on drought stress. It seems to me that some people intentionally stress the plant and then apply various bio-stimulants that help alleviate the stress.
Personally, I have always preferred to keep the grow medium moist but not wet, regardless of what medium I have used. When the medium is dry, I can easily add more water. But when it is too wet, it can cause a lot of problems. I have attached the study, but the conclusion is below.
My focus is more on drought stress and less on si accumulation and its advantages. Is there something there with drought stress or are regular efficient watering practices best. Im currently using rockwool after growing in coco in a commercial setting for several years and we are experiencing the fastest growth we have ever seen.
Conclusion
Precision drought stress reduced height and dry mass in Cannabis compared
to well-watered treatments. Silicon (Si) supplementation did not benefit Cannabis
under drought stress in these studies but reduced powdery mildew infection of Si
supplemented treatments on the aerial shoots due to the accumulation of Si in tissues.
Precision drought stress has shown potential but requires further study in Cannabis.
I’ve read that in studies. In marijuana I would think light stress would be better or even salt stress through high ec. I started questioning if I’m hurting yields with drought stress.
The fact we add silica and fulvic through irrigation and foliar kelp just got me thinking. Why create so many abiotic stresses to then apply products that counter it.
One question essentially led to many more questions
Humic acid content in soil helps tremendously in getting through dry conditions. Once again, this is with vegetables, but there are probably some cannabis parallels.
100% agree. The parallels are there for sure. Just curious if extreme drybacks are worth it, especially in rockwool. We just received our order the other week from @agtoniik
I’m surprised myself at how fast the growth is. We essentially going to cut our veg time to about 10 days. In Coco we were always at 2-3 weeks
I’ve been reading up on water use efficiency as well and trying to get a better understanding on how to optimize my inputs and equipment.
It’s almost impossible to cause soil like drought stress in coco and especially wool until you’ve gone far too dry. It’s my understanding that in soil-less media EC stress simulates a controlled drought stress because you are effecting the matric potential of the media. I usually describe this as low EC is a short straw and raising the EC is lengthening the straw making the plant need to pull harder to get what it needs.
If you are running a high VPD environment, excess EC stress would not be proper steering.
My experience, controlling the stress at the end of flower greatly effects flowering time and quality. Not applying any stress would increase yields but you will extend flower time and lose some of what most of us classify as quality. The extremes work much less effective then a more nuanced approach to EC control especially when indoor. Greenhouse growing adds more complexity as VPD swings can be extreme.
What’s considered high? Keep vpd floating 1-1.20.
From research and experience I’ve found running higher ec and watering less works good because in high co2 environment keeps the stomata closed at 50% since the plant doesn’t have to work as hard for co2. I don’t understand the mechanics completely but I know wue is increased with co2.
Depending on the strain we keep EC around 3-3.2. co2 1150-1200. Biggest differences between Coco and rockwool I have noticed is drybacks. Last harvest with Coco we did 91 g/sqft. Essentially trying to do at least 80+ g/sqft this first run with rockwool.
I consider that normal VPD, 1.3-1.5 I would consider high but still healthy. Multiple VPD points can work as long as everything else is dialed in around it. At a lower VPD you can push dry back and EC a little harder.
I’ve had my veg in wool and flowered in mostly coco until this last year, I recently started playing with slabs for flowering and that is probably my preferred way now.
What do you like about slabs over blocks? We currently do 444 to 665.3. I thought about going slabs instead of 6’s. Definitely like the cleanliness and efficiency over Coco. Man power and labor seems more efficient as well.
I mean this is absolutely true. The healthiest i’ve seen plants of mine was when I experimented with small small small drip emitters running at 15 minutes at a time several times a day. Top layers of soil are so dry i’ve had friends of mine think it was clogged but the girls were still straight up praying with serious chunk forming on the colas. Ghetto drybacking ftw
Ive had issues with ph swings via longer dry backs using coco and wool. Keep detailed notes and its taken me years and i still grow mids.
Happy Holidays errone
We could have a long conversation about soil-less media and pro/cons. I’ll try to summarize my opinions.
Coco is better at adapting to your system, wool needs to be designed around it more.
A lot of engineering and information is know about stonewool culture. Grodan can be thanked for this in large part. Blocks were never designed for fruiting, they were designed for scaled flood and drain for mass propagation to transplanted into/onto another media. This is why the fibers are vertical. Slabs were the intended long term media for fruiting. Horizontal fibers and height play a huge role.
Have you ever stacked two blocks on top of each other? What happens to the top block even if no plants are in it? It pretty much completely dries out. This fact alone makes stacking blocks literally make zero sense, I understand people do it but wool was never meant to be used this way. What happens when you stack a block on a slab? You gain that as additional media, as the top block stays hydrated and functional. I’m not including 6x6x6 blocks in this statement.
Now slabs were designed and engineered around vegetable production not cannabis. Media volume/sf for your crop matters and it has been my experience that a 3x6x36 slab is far too much media for that spacing for cannabis. 4x8x9 is an amazing slab for large greenhouse style plants but for indoor both of those options are less than idea, for a few reasons, but primarily goes back to what I said first about wool.
Now, a 6x6x6 block and a 3x6x12 slab are the same volume but the dynamics and water holding capacity are drastically different.
Interesting info about the direction of fibers in blocks vs slabs.
I’ve never heard that before but it makes sense.
I would like to hear more about this from people with experience if you wouldn’t mind.
Rockwool seems more risky and easier to mess up by drying back too far but it’s very consistent from batch to batch.
Coco seems less risky as far as drybacks but you can have wildly varying quality between batches. There is also the issue of potentially needing to wash/buffer and worry about CEC issues. Maybe some of this is different with these new compressed coco bags but I’m just trying them for the first time.
Let’s have that long conversation. I’m interested to hear your experiences.
My first experience with rockwool was in 2015 for about 6 months before switching to something else. Our first run with wool at this facility. This was day 7 of flower and about 3 weeks from being 6-8 inches clones.
4 inch cubes vegged about 10 days and we were forced to transfer to larger cubes because roots were growing out the bottom crazy. Clones were growing into the lamps on the double tier racks. We kept the wool moist most of the time in veg around 50-55%. At the time I thought it was too wet but I was wrong as they healthy and growing fast.
After transferring to 6 cubes it took about 2-3 days for the blocks to work themselves out and perform consistently. I noticed what your saying, the top block dries out and becomes a stem of the plant in a sense. However I like how the top block makes the water disperse on the lower block better than the dripper does. It’s like the water spreads then gravity kicks in. I noticed with water content sensors it will be weekly adjustments and recalibrations.
As stated some blocks perform better than others, usually the ones that run dryer are the trouble makers and seem to never get back right. So I will say there is inconsistentcy with the flower lot and noticed the same when we move clones to the veg racks.
I don’t see how people do extreme drybacks with wool to begin with but that’s something we plan to shy away from as wool just does not perform like Coco at all.
Coco: Coco has a significant overwatering zone. This means that even a slight increase in tension results in a notable drop in volumetric water content. This zone can potentially lead to reduced oxygen availability to the roots.
Rockwool: Rockwool, on the other hand, doesn’t have a pronounced overwatering zone. The tension increases more rapidly with very little drop in volumetric water content, making it less prone to overwatering issues.
Drying Characteristics:
Coco: Coco exhibits a slower decline in volumetric water content as tension increases. This indicates that, for coco, the plant needs to exert more effort to draw water from the media as it dries.
Rockwool: Rockwool, in contrast, shows a steeper decline in volumetric water content as tension increases. This suggests that the plant can more easily extract water from rockwool as it dries.
Here is a great video by @danielfp further explaining moisture retention curves:
Humic acid tends to be for soil, but it’s absolutely true. I dry back 30% with fulvic acid. As others have mentioned in this thread, keep an eye on your pH going up when you do this. It allows elements to be absorbed at all pH ranges.
interesting discussion but don’t you guys use clay pebbles these days? is there a reason u prefer rockwool/coco like prefer run to waste than recirculate? am in N.europe and used to use rockwool in 1990s for flowering but these days only use for rooting clones or starting beans. The clay pebbles offer more control over moisture level and far cheaper can be re used. When used to run ebb&flow could flood maybe 4 or 5 times a day with rw (4in cube) over 12hour period without satuation whereas with clay can flood every hour so more air exchanges better growth.
