Calcium Deficiency: Signs, Causes and Cures

The most common nutrient deficiency that our customers face is a calcium deficiency.  When you encounter it for the first time, it can be scary.  You might freak out and think your plants are dying.  They're not, they're just showing you that they need something.  It is very easy to diagnose and fix, hopefully this helps.

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

Causes:

- 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.)

- Under-feeding

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

Flushing

Flushing is something that a lot of people seem to be confused about.  Either they don't do it at all, or don't know if they have to do it, or THINK that they already do it when they don't.  There are two different types of flushing:

1. The periodic flushing of your medium, to leach the salts out to avoid salt and nutrient build-up (or the mad flush after realizing that you've already over-fertilized in an attempt at damage-control).

2. Flushing during the final week of the plants blooming cycle to remove synthetic nutrients and salt build-up from the plants themselves, to avoid a chemical taste in your fruits and vegetables.  

Let's start with the first one.  When using a porous medium, such as soil, rockwool, a soilless mix (Pro-Mix, Sunshine, etc.), a periodic flushing is always recommended.  The way plants use nutrients is like a conveyor belt - they use what they need and leave behind what they don't.  Over time, the excess nutrients build up in the medium and can lockout the useful nutrients that the plants want.  Also, most fertilizers contain salt.  When the salt builds up in your medium the plants begin to absorb it along with (or, if it's bad enough, instead of) the nutrients.  The best way to catch it before it's too late is to measure your run-off with a PPM/EC meter.  If you're feeding your plants 1000 PPM, and the solution coming out the bottom of the containers/cubes is measuring higher, you know there are other nutrients or salt building up in your medium.  Unfortunately most people only know after-the-fact, when their plants are starting to show signs of over-fertilization and salt buildup - the leaves of the plants begin to curl upwards, they begin to burn at the tips (or if it's gone even further, the whole leaves start to burn up and get crispy).  This will stunt the growth of the plants and if allowed to go on for too long, the plants can die.

Flushing is not the same thing as just watering your plants with plain water (a very common misconception).  In order to remove all buildup from your medium, you need to either use a salt leaching formula (such as Clearex from Botanicare) that will bind to the salt and help remove it faster, or use a massive amount of water.

If using plain water with a soil or soilless medium, you need to use close to 3x the amount water as the size of the container you're growing in (if you are growing in 5 gallon buckets, you would need to pour about 15 gallons of water over each plant).  If using Clearex, 2x the water is usually enough.  This requires something to catch the water you're flushing with, like a big reservoir or a bathtub, or the most ideal thing would be a floor drain.  Have your PPM/EC meter with you and measure the run-off.  At the end of your flushing your PPM/EC reading on your run-off should be almost identical to that of the water you're pouring in.

If flushing in a hydroponic system with rockwool as your medium, I'd recommend draining the reservoir of all nutrients, filling it with plain water and adding Clearex at its maximum dosage (the bottle says 1/4-1/2 oz. per gallon of water, use 1/2oz./gallon).  Measure your PPM before it comes in contact with the medium, then run your system for an hour or so.   After it's been run, take a fresh gallon of water and clearex and pour it over the top of your rockwool cube.  Measure the run-off and hopefully the PPM's are close.  If not, run the system for another 30 minutes to an hour and measure again.

This should be done about every 3-4 weeks.

Now for the final week flush.  When using synthetic or chemical fertilizers, the flavor of your fruits and vegetables can be affected.  Especially when using a three-part fertilizer (like General Hydroponics' Flora-series), the iron in the Micro can leave an unpleasant metallic taste.  The best way to combat this is to remove all fertilizer from your feeding regimen for the final week of flowering/fruiting before harvest.  Add a FINAL flushing agent (different from a salt-leaching formula) to your water like Final Phase from Advanced Nutrients.  Final Phase has chelates in it that bond to heavy metals and nutrient salts and remove them from the plants themselves, not just the mediums.  Some people like to add a flavor enhancer to their final flush (like Sugaree, Sweet or B. Candy) so they get the benefits of the fruit extracts in those formulas, but Final Phase is designed to retain essential oil production so your fruits' natural flavors won't be lost.