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Capitol Corridor
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Capitol Corridor

Now I Know My N-P-Ks (Next time won't you plant with me?) Part Three

We have come to the third and final installment of my series discussing the three  macronutrients essential for a healthy garden.  My first blog was about nitrogen, why it is needed in the garden, what it might look like if there is a deficiency, and what do do about correcting it.  The second article was about phosphorus.  This final submission of the series is about potassium.

To catch you up, these three essential macronutrients are contained in the bag or bottle of fertilizer you purchase.  However, unless you are informed, you will simply see three meaningless numbers listed there, e.g. 5-10-5; or 12-10-5.  You must know that these numbers refer to the percentage of each macronutrient included, and these are always in a specific order;  nitrogen (N), phosphorus (P), and potassium (K).  In the first of these examples, the fertilizer contains 5% nitrogen, 10% phosphorus, and 5 % potassium.  Use these numbers to decide which product you need to purchase for your gardening needs.  

So why do we need potassium?  Potassium helps regulate photosynthesis, moisture content of plant cells and stomata, which controls the carbon dioxide exchange.  Potassium helps move vital nutrients around in the plant itself.  It also aides in the formation of proteins, which directly effect the nutritional value of the fruit.  Lastly, potassium aids the soil as it is responsible for fixing nitrogen in legumes which need a potassium rich soil.

What would a potassium deficiency look like?  It would be much subtler than a nitrogen or phosphorus deficiency, even to the extent that you might not notice it.  Your plants may appear a bit smaller or thinner than expected, but they do not look "sick". There are a few symptoms to be on the lookout for, however.  If your plants appear weak and spindly, attract more pests than usual, and/or plants bear small, thin-skinned fruits that are lacking in flavor, you most likely have a potassium deficiency. This deficiency, as with the other two, can be remedied by composting.  

Another highly recommended remedy is the use of greensand.  This is really green, and has the consistency of sand.  Add 10 pounds per 100 square feet to a new garden.  Add it to your compost pile also to ensure against future.   It also contains iron, magnesium, calcium, phosphorus, and more than 30 trace elements.

Wood ash contains about 5% potassium in a relative quick release form.  Spread on a new garden without plants (late fall or winter), as the ash can actually burn plants. A third recommendation is granite dust.  It will provide a water solvable potassium that your plants can use immediately.  Granite dust is about 3% immediately available, and 3% available over time.  It will not effect your pH balance.  (pH balance?  Ah, fodder for another blog!)

Ground kelp has been noted as a source of potassium, but its percentage is less than the above mentioned additives.

In reviewing these macronutrients, it is clear that all of them are essential.  Most likely, like the vitamins our bodies need, if your garden is lacking in one, it is lacking in others.  As I review the differences in the appearance of the deficiencies, I see more similarities the differences.  I have come to the conclusion that I must not only keep feverishly composting, but actually increase the amount I compost, as compost contains the nutrients required by most plants.  Then, if that fails, and deficiencies continue to appear, I will have my soil professionally analyzed.  There are testing kits available for around $11.00, but in researching these, I found numerous reports of unreliability.  Instead, I would recommending using the UC Davis Analytical Lab.  Information on how to use this resource, the costs, and the procedures are available if you simply put UC Davis Analytical Lab in your search engine.

I have learned a lot from writing a three segmented blog about N-P-K, but I must admit what has really increased is my ever growing awe of nature and how it comes together and works to produce what we need.  Little, tiny, invisible nutrients effecting big leafy, greens--with or without my understanding.  Remarkable!

Posted on Tuesday, June 25, 2013 at 6:06 PM
Tags: essential (1), fertilizer (12), Nitrogen (13), nutrients (1), phosphorus (2), potassium (1)


It's my understanding that worm-created compost is rich in potassium. Some might say almost too rich if overused.

Posted by bil paul on June 29, 2013 at 11:27 AM

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