Brown spots on leaves

[bebop]

I'm sure this has been brought up before...I'm a first timer, started with two plants. Both germinated on a wet paper towel, planted in Rapid Rooters in a pint-sized plastic pot of coco coir mix (with drainage holes). After a week or two, I started noticing brown spots on the lower leaves of one of the plants. I'm watering when the soil seems dry (first knuckle), about every 3 days. pH is correct (about 6), and using a low level of nutrients every other watering. I repotted them both, each in their own 5 gallon pot, and they seem to be doing well, but the one still is developing brown spots on the lower leaves. The other is not...what's going on?

[Tersky]

Did you buffer the coco first? Are you using cal mag? Tap or filtered/distilled? I typically dont water until pot is light. This allows roots to spread out searching for water/nutes. It also lessens the risk of root rot from overwatering. Personally, i feed every time i water, but also use RO water so my ppms are on the low side. Finally, it could be going through transplant shock, tho i have never had transplant shock that severe.

If it were my guess from the pics, you possibly did not buffer the coco which then causes deficiencies and stunted growth.
"Why You Need to Buffer Coco Coir

There are cation exchange sites in coco that will interfere with nutrition until they are buffered. The cation exchange sites in coco naturally come loaded with sodium (Na) and potassium (K) cations. However, the Na and the K are only weakly held to the exchange sites. In the presence of calcium (Ca) or magnesium (Mg), the sites will release their Na or K cations and lock onto the Ca or Mg. These processes are known as “cation exchanges”.

Buffering coco is accomplished by soaking it in Ca and Mg. This allows the cation exchanges to take place prior to adding plants. Simply soak your coco in a solution of Cal/Mag water and the exchange sites will release their K and Na cations and lock onto the Ca and Mg. When the cation exchange sites bond with Ca and Mg rather than Na and K, it is “buffered”. The bonds that hold the Ca and Mg to the sites are very strong and cation exchange will largely stop. This means that all of the nutrients that you add to the water will be available to the plant at the ratios that you provide them.

Growing in Un-Buffered Coco

Many growers are unaware of the need to buffer the coco and they try to grow plants in unbuffered coco. In unbuffered coco, the cation exchange sites will strip the nutrient solution of the Ca and Mg and replace those cations with Na and K. This creates a sub-optimal Nutrient Element Ratio (NER) and renders Ca and Mg unavailable to the plant.

Failing to buffer the coco is why so many growers suffer calcium deficiencies in coco grows."

taken from https://www.cocoforcannabis.com/how-...fer-coco-coir/

[TOKABIGONE]

bebop that was an excellent technical explanation by Tersky of the chemical processes that need to occur for nutrients to be available to the plants. I found in coco with perlite {hopefully!}. that pH is best maintained at 5.5 to 6.0. At same age I had brown spots and yellowing areas. New growth looked much better in just a few days. Spots and yellowing will remain until those leaves fall off.

There is however I think maybe another issue with over watering and possible root rot as a result. Are they still in the pint cups? A drainage problem perhaps? Feeling the weight of your containers both dry and wet is a great way to know when they need water. Read the tutorials on watering and transplanting on the main site.

You could slide the plant out of the pot enough to see and smell the roots. White and fresh earthy smell is good, brown, slimy or smelly bad. Cut your losses at that point or if ok then go ahead and put into a pre-prepared larger pot.

Best of luck to both of you!

[bebop]

Thanks to both of you for the help and explanation!

I am using CalMagic, but I had never heard of buffering the coco coir, so perhaps that is the issue. I think when I had them in the smaller pots, they were starting to get root bound (the cups were semi-clear, and I could see roots along the outside of the soil. That's when I re-planted them). At that point, I was also thinking that the roots ay be getting too much water. After re-planting , they did better, and seemed to spread out more, but then the one continued to get spots on the leaves. The newest leaves seem ok, though they are curlier than the other plant.

That's another thing that puzzles me; both plants were treated exactly the same, but only one has exhibited this problem. I'm not complaining--I'm glad one of them is doing better, for sure!

Anyway, I'll know to buffer the next time, if I use coco coir. I may just use potting soil, though--does that also need buffering, or can I use it as is (adding some nutrients as I go along)?