Hi Gee,
@Azimuth pointed me here because I experienced exactly what you described. Gang buster veg, calcium deficiency after the stretch. My first grow only 1 of three plants experienced the post stretch deficiency, however in my current grow both plants experienced deficiency's after the stretch. I was able to remedy most of the issues by top watering the SIP's like you described and it looks like I'll have an ok harvest.
I was thinking back to my first SIP grow and why 2 of the 3 plants showed no deficiency but were grown in the same SIP setups. It occurred to me that those 2 had their soils mixed at the same time and I added more perlite to them because the bagged soil seemed to be little light on it. Throughout the grow these 2 plants were constantly drying before the 3rd which was showing CalMag spots and leaf burn. Could the extra added perlite in those 2 plants make that kind of difference or did I just get lucky?
Either way thanks for writing this in a slightly dumbed down way so that I could make heads and tails of it. Plus I was a Lego kid growing up so I can relate
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G13, Welcome
It's 2 things at play really. One is lack of oxygen because the soil is too wet.
Extra perlite can definitely lessen this, but it can also add to it too. Perlite is porous so it can move air or water.
So as it dries down it can move a lot of air and it drains well. That means if you let your reservoir dry down, your soil will drain from the top down as the reservoir drops, and that pulls air in from the surface, but when you fill the reservoir again, capilliary action will raise the water up thru the perlite and push the air back out the top, so the key is the water stick.
Wait until your soil needs water, then only put enough in the reservoir so if it becomes too wet on the water stick, 12 hours later it isn't.
Any longer and you added too much to the res, and really you should shoot for 8 hours tops.
The 2nd is calcium. Its heavy and sinks. It's also extremely mobile in water, so soil too wet and calcium falls out the bottom.
So you need to add it up top and top water it in, or add calmag to the reservoir, which will work but calcium is heavy and is easier to let "fall" thru the soil than raise from the bottom, plus top watering grow feeder roots.
If your soil has been too wet you will have hydroponic roots so the reservoir may be a better approach to fix a deficiency, but moving forward on new grows, filling the reservoir by allowing it to catch runoff from well areated soil is better.
Then there is soil carbon. It absorbs water. Lots of it.
It's job is to run your CEC and retain water. Water mixes with bug poop in the soil and absorbs into carbon to be held as soup until roots suckbit dry, and it's the CEC, so as they suck it up, cations get pulled into the soup too.
Too much carbon and soil gets soggy. Not enough and it needs too many waterings. Just the right amount and it is just right.
Different carbons have different densities so hold different amounts of water. Wood holds more than coco or leaves, etc. There are different charts all over the net.
Different carbon sources have different carbon:nitrogen ratios. The higher the carbon number the more water it will hold.
So denser carbons need less in a pot, less denser means you need more in a pot. Carbon takes up room so it's a juggling act to balance carbon size in the pot vs food size, and perlite also takes up space, so it's linked in too.
The juggling begins, but by using a larger pot you can accomodate this too.
So balance once again is key.
I prefer coco or aged composted wood. Coco is best IMO because it releases K as it decomposes, but it needs to be fully replaced every rebuild.
Fine aged bark recycles better but more perlite is needed as it's denser as each speck of it holds more water. So I prefer 10gal pots over smaller ones to accomodate more perlite.
This is where following a reputable recipe simplifies things, and if your plant gets hungry before harvest, use a bigger pot next time.
It's all about balance on every front.
So here is an important thing to remember.
Soil is porous by nature. Those hallways in your soil can hold air or water.
Water in the hallways replaces air.
You need to run water thru the hallways to recharge the carbon with water, but all the water in the hallways needs to drain out after the carbon is rehydrated.
That combination of wet carbon and dry hallways ensures both air and water are abundant.
Any piece of food that can't be attached to an oxygen molecule can't be recognized as food, so water in the hallways can and will lead to starvation even if the pot is full of food.
That's what happened to Azi. He was trying to fix it by adding and adjusting food.
I showed him that draining the hallways was what he needed to do.
Balance.
Hope that helps
So add calcium up top, run it thru the hallways, and let the reservoir catch the runoff. Then use a water stick to monitor.
If the soil is too wet 8 hours later, you have water in your hallways, drain the reservoir.
Measure how much water you add and how often until you dial in your practices for the recipe you are using.
Then if you are in LOS, start chasing brix.
An analog refractometer will tell you your brix reading, and it also tells you the state of calcium.
A dollar for a cheapo water stick and $25 for a refractometer is money well spent. It leads to cheap fun
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