Hey can you explain a little bit about how it works using tissue samples?
How do you know whether to take samples from young or old foliage?
How long does it take you to get a sample back from the lab you’re using? I image it has to be pretty quick in order to make the test results useful.
How do you know what standard to compare your results with? (For example, how do you know the reading in your tissue sample is high?)
Hey I was wondering if you by any chance listened to the latest episode of “We the Growers” podcast?
If you haven’t heard of it it’s a podcast put out by the company Athena, usually just talking about their products.
On the latest episode they had Dr. Bruce Bugbee on talking about various subjects. One of the things he says is that he is starting to recommend a pH of around 6.5 for cannabis. I believe he said that they are finding that cannabis does not have much sensitivity to excess iron, which he says is a main issue with higher pH. The higher pH prevents issues with micro nutrients he says.
He also said that if what you’re doing currently with your pH is working then there’s no need to change, so maybe it’s not the biggest deal in the world.
There was more that he mentioned (something about manganese being mobile?) in the podcast and I am going to give it another listen and make some notes to share here.
Cannabis has a tendency to decrease the pH in the media during mid to late flower, which is the reason why Bruce is recommending a feed at 6.5. This is so that you can compensate for this drop. Since the Fe uptake is not affected very much at this point, there are not likely going to be any uptake problems from going in this direction. This is probably feasible at the EC values Bruce generally grows at, which are in the 1.5-1.8mS/cm range (except when he has tested high EC levels).
With that said, with the P and Ca concentrations generally used in most commercial formulations, an increase of pH to 6.5 on the lines will almost inevitably lead to clogging of the lines with probably disastrous results. For most formulations, feeding at a pH of 6.5 is going to be very problematic, especially if the EC values are >2.5 mS/cm. Not because of uptake issues but because of chemical issues inside the lines.
While I was scanning over Dr. Fernandez’s paper “Principles of Nutrient and Water Management for Indoor Agriculture” I think I stumbled onto the answers to one of my questions about where to take tissue samples from.
" The most definitive method for determining optimal nutrition is analysis of leaf tissue combined with crop yield, but leaves vary based on their position and age of the plant. Standardized sampling techniques are reviewed in the Handbook of Reference Methods for Plant Analysis [82]. The uppermost fully expanded leaves are a standard for analysis because they are actively growing tissue. These leaves provide a good indication of whole-plant nutrient status. Lower leaves are less representative because they can have low concentrations of mobile nutrients such as N, P, and K (especially when these nutrients are in limited supply) and high concentrations for immobile nutrients such as calcium and boron [75]. Tissue analysis of upper leaves may not reveal deficiencies in lower leaves. Upper and lower leaves should be analyzed if there are visible nutrient deficiencies or toxicities."
The book mentioned (Handbook of Reference Methods for Plant Analysis) is also available online and has sample-taking methods outlined for various types of plants but not cannabis.
We have the flower mix down pretty good but to be honest we’ve had issues with veg and up until about day 14 of flower, when I started this I was supposed to be getting a hand from someone with lots of knowledge but at basically day 1 he went mia unfortunately.
For the last 6 months I’ve been trying a bunch of different things in veg and the last month has been the best it’s been, I think I’ve been over feeding N and with the high Transpiration rate from the hps they are just sucking the N right up.
All the agronomists I have been studying lately seem to suggest that this is pretty much mandatory when troubleshooting plant nutrition issues because certain problems can look like each other making it hard to tell what’s what and toxicities can look like deficiencies adding to the confusion.
I have been, but it’s just not easy as adding what’s deficient. We are starting to get closer and I think a lot of our issues are coming from over feeding nitrate in veg. I used to use cmh in veg and flower in my medical grow and seems like the Transpiration rate groom cmh is much closer to led then hps, that being said I think the extra transpiration from the hps has the plants uptaking more N then required.
I recently watched @danielfp 's video on using calcium sulfate (gypsum) as a nutritional salt.
It has a low solubility (2.5g/gal) at room temp and has retrograde solubility (gets less soluble as solution is warmed) but is still able to supply all the plant’s calcium needs if you wanted.
100mg/L of CaSO4 (gypsum) adds 23ppm Ca and 18ppm S.
At the max solubility of 2.5g/L this could add 582ppm Ca, more than enough for plants.
One of the drawbacks is that the low solubility prevents the use of concentrated stock tanks, you must add the diluted salt directly to the reservoir.
Here’s an interesting gypsum dilution tank I saw from Bear AG that made me think about this topic:
Is anyone using gypsum to reduce N while still maintaining Ca toward the end of flower or just as part of their regular nutrient regime to supply Ca and S?
Maybe it could be used instead of or in addition to CaCl2 (Athena Fade)?
You could definitely use gypsum for this purpose. However few people do so because it’s not really compatible with direct injection-to-irrigation systems. If you have the possibility to add it directly at any point then it would certainly fit the bill and wouldn’t add any chloride to your flower.
Another possibility is to add gypsum as a top dressing additive to your plants at this later stage.
I have been using jacks 321 in promix hpcc for about 6 months now. Its not perfect by itself but with compost teas and top dressing amendments I think its great . Only thing im not a fan of is both of the bloom products for the first 1-2 weeks and final week before flush have no calcium . Im pretty sure its a salt compatibility issue the calcium nitrate would cause the salts to precipitate out of solution . So i have been battling that problem by feeding lots of compost teas and top dressing the soil so there will be a slower release of calcium and not just entirely cut it off . I use terp tea from roots organic . They have a calmag that is mainly gypsum does anyone know if it would be compatible with the jacks 321 bloom and finish ? Really want to try top dressing the soil with some but was worried about compatibilty issues
