Signs:
The first sign of a calcium deficiency is yellow spotting on the leaves. If left untreated, the yellow spots will start to become brown in the center and will eventually spread over the entire affected leaves. They will then start to dry out, shrivel up and die.
From issue 24 of CannaTalk Magazine
- Unbalanced pH.
pH is one of the most important factors in gardening. If the pH level of your growing medium or nutrient solution isn't in the proper range, typically from 5.5 to 6.5, certain nutrients can't be absorbed by the plant. So even though you may be feeding your plants everything they need to grow well and perform, they might not actually be taking it in. You can check your pH with a variety of tools. For testing water: paper pH test strips, pH indicator solution (General Hydroponics makes an inexpensive test kit, and a complete control kit that comes with pH Up and pH Down to adjust your pH) or a digital pH pen. For testing soil: A soil tester that is cone-shaped with a dial or a Bluelab digital soil pH meter (the inexpensive pH testers with the long metal probes are unfortunately not very accurate). With container gardening, you can always test the water you're feeding your plants and then the run-off from the bottom of the containers and "ballpark" the difference (for example, if your water is reading 6.0 and your run-off is reading 7.0, you can safely assume your medium has a pH of around 8.0).
Cure: In hydroponics, you can simply adjust the pH of your nutrient solution with pH Up (which is alkaline) or pH Down (which is acidic). In soil it will take a little longer to stabilize the pH (it takes longer to fix any problem in soil than it does in hydroponics), but you would do it using the same principle as reading the run-off. For example, if your soil has a pH reading of 4.0, you would want to water with a solution that measures 8.0 for a few waterings to bring it up to 6.0.
- Using nutrients that don't have a high enough dose of Calcium.
New York, especially the five boroughs, has some of the cleanest water in the country (minus the chlorine) which means that it doesn't have a very high nutrient/mineral content. This is typically a good thing because when your water starts out with a low PPM/EC/TDS/CF (all of the units of measure that are used to measure the amount of "stuff" in your water), you have more room to feed your plants the nutrients that they actually want and need. When your water starts out with more "stuff" in it, you are limited in how much you can add to it to feed your plants. When starting with water with a very low PPM (Parts Per Million, which is the most common unit of measure in the US in our industry), you have to make sure that you're adding all of the essential micro and macro nutrients for plant growth, in the proper ratios for the specific stage of growth that your plants are in. That sounds complicated, but most of the base nutrients you see have a pretty well-balanced blend of these elements. That said, sometimes plants need more.
Cure: Use a calcium supplement (usually a blend of calcium and magnesium) such as General Hydroponics' CALiMAGic, which contains 5% calcium, 1.5% magnesium, 1% nitrogen and .1% iron (all of the most commonly deficient nutrients in the vegetative stage), or Aptus' Massboost which contains 7% calcium, 5% nitrogen and 1% magnesium. Within a week or 2 this should fix your calcium deficiency. New growth should start looking green and healthy. (If you'd like to speed up the recovery process, when your plants are in their vegetative stage you can foliar-feed the Massboost. Just be sure to follow their recommendations for foliar-feeding and always spray when the lights are off, or at sundown if growing outdoors.)
Sometimes plants just want more food. If your pH is on point and you're using a good nutrient that contains a higher percentage of calcium, look for signs of other deficiencies. For a chart of what all of the major nutrient deficiencies look like, come in for a free copy of CannaTalk issue 24. If you see signs of a calcium deficiency, but maybe it looks like a nitrogen deficiency too, and also kind of iron (or some other mix..) you might not be feeding them enough.
Cure: Try and increase the amount of food you're giving them, but be very careful. Adding too much, too soon, can cause over-fertilization and burn your plants. This is when a PPM meter comes in handy. You can know exactly how much you're feeding your plants and make notes of what they want, and when they want it. We usually recommend increasing your nutrients by only 100-150 PPM at a time.
- Nutrient Antagonism
Sometimes when it looks like you a have a deficiency of one nutrient, it's really because you have an excess of another. This is known as "nutrient antagonism." An over-abundance of potassium and/or salt is a very common cause of calcium deficiency when using coco coir as a growing medium. Coco has a lot of naturally occurring potassium and sodium (sodium due to the sea water that is present where the coco is originally grown) which is an antagonist of calcium.
Cure: When growing in a coco coir medium, be sure to use a high quality brand! Canna Coco has already been treated and buffered to correct any nutrient/salt excesses beforehand so it isn't an issue, but a lot of other brands have not been treated the same way. This is why many people have negative results when using sub-par brands of coco coir. Just add a good quality calcium supplement to your nutrient regimen and the problem should correct itself. If you're growing in a soil or soilless medium, such as Pro-Mix or Rockwool, just give the plants a good flush (see our article on Flushing) and the next time few times you feed, add in a dose of a calcium supplement.
From Aptus' Education Manual
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