Cannabis nutrients part one: Primary and Secondary nutrients.

by Alex Robles

Greetings everyone, today is a beautiful day and I figured it would be a good time to start talking about plant nutrients.  Now depending on what book you read or who taught you how to grow, some of this information may be different.   In this series of posts we’re going to talk about the when and the why plants  absorb nutrients.

Primary Nutrients

Almost all plant life uses the primary/macro nutrients of nitrogen (N), phosphorus (P), and potassium (K) as the major building blocks for developing a strong, healthy root system and beautiful green foliage.  They are known as macro nutrients because they’re needed in large amounts.  But different plants take up these nutrients in different ways at different times in their life cycle.  Plants like vegetable and cannabis will absorb certain nutrients easier when they’ve been processed by bacteria.  More woody plants or plants with some sort of bark on them like shrubs and trees will absorb those nutrients in a more complete form.

The NPK ratios should be clearly printed somewhere on the label of most bagged soil, bottled nutrient or fertilizer.  The first number is the nitrogen, the second is the phosphorus and the third is the potassium.  These ratios are important because you don’t want to over or under feed your cannabis plant during an important cycle.  If your soil or worm castings say 20-10-10, that means it has 20% N, 10% P and 10% K by weight.  If your bottled nutrient or liquid fertilizer say 10-20-10, that means it has 10% N, 20% P and 10% K by volume.

During vegetative growth I alternate between a liquid fish and kelp fertilizer that is a 2-2-2 and beneficial microbes for every other feeding/watering.  While in flowering I cut down on the nitrogen and increase the potassium to a 0-1-3.  I’ll stop feeding the plant nutrients and microbes and start flushing the plant 2 weeks before harvesting in order to give the plant a chance to use up and sweat out any nutrient that might be left in the soil and water leaves.

Secondary Nutrients

Secondary nutrients are calcium (Cal), magnesium (Mg), and sulfur (S) and are sometimes labeled as CalMagS.  These elements are sometimes lumped together with the macro and micro nutrients.  Me personally, I like to keep them in their own category because they’re not needed in the same, larger amounts as N.P.K.

When a nutrient deficiency in cannabis shows up, you can make a pretty good guess of what it is by where it starts.  In an iron, calcium or sulfur deficiency the symptoms will usually start with the top, newer growth and move its way down.   During a nitrogen, potassium, phosphorous, or magnesium deficiency, the symptoms will show up on the older, lower growth and move its way up.

In this series I’ll go over the some of the “Good” (why a healthy plant needs a nutrient), the “Bad”(what a plant looks like when it has too much nutrient) and the “Ugly”(what a plant looks like with too little nutrient) of plant nutrients.

Grow, Learn, Teach

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