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!

I love pouring over seed catalogs and gardening magazines.  I greatly enjoy picking my sweet peas and harvesting  my chard and lettuce.  I relish writing about gardens and sitting at our Master Gardener's table at the Vacaville Farmers Market on a sunny Saturday morning, talking with home gardeners about their plant problems and chatting with fellow Master Gardeners.

What I do not love has been trying to learn the technical side of gardening--the chemistry, the science of what makes it work.  I got as far as biology in high school, but became turned off to science at the dissection of that poor frog.

However, as an adult Master Gardener, it is time I looked reality in the eye, planted my feet firmly on my nutrient-poor soil, and learn some science.

I have decided to to start with nitrogen.  Why?  Because it is the first number listed on fertilizer labels, and I really want to understand what that means.

Researching  nitrogen, I discovered it is the 5th most common element in the universe and makes up 78% of the earth's atmosphere. Bringing it down to more useful information for a gardener, nitrogen is an essential nutrient that is a naturally an inert gas which needs  to be  "fixed"or drawn  out of the air and converted to a form usable to a plant.  Simply stated, plants without sufficient nitrogen display poor or stopped growth and/or pale green or yellowing leaves due to the fact that they are not able to make sufficient chlorophyll.  Therefore, photosynthesis cannot occur.

One can recognize nitrogen deficiency by noticing spindly stems, the pale or yellowing of leaves, especially of the most mature ones, and wilting of sufficiently watered plants, even if the weather is not overly warm.  It is good to know which plants are most commonly are effected by nitrogen deficiency so as to keep an eye out.  These are fruit trees, vegetable plants, and broad leafed evergreens.

The good news is that gardeners can manage the nitrogen content of their soil several ways.  One method is adding organic materials by actually planting crops in the fall or very early spring that fix nitrogen.  These would be legumes used as a cover crop, including alfalfa, clover, hairy vetch, or peas, as these plants actually work the bacteria in the soil to absorb nitrogen from the air and place it in the tiny root nodules.  This is called "nitrogen fixation".  These plants, when mature, are to be chopped up and dug into the soil.

Another material to get nitrogen into the soil is manure from grass eating animals.  Let the manure age at least 6 months before using to prevent burning of your plants.  Poultry manure is also a good source, but let it air out for 4 months before using.  Bone meal is a fast acting fertilize,  but can also burn plants.  Mix with water or dig it lightly into the soil.   Crab meal, feather meal, alfalfa meal, soybean and cottonseed meal are all also recommend.  Just be very sure to do a little research, know what your plant needs, and follow directions exactly.

So what does all this have to do with that first number on the fertilizer bag?  There are always three numbers, and those numbers simply tell you what the percentage is of each of the three main nutrients found inside the box.  The first number is for nitrogen, represented in chemistry by a capital "N". The second number is for phosphorus, represented by a "P", and the third number, represented by a "K" , tells you the percentage of potassium.  So if you are wanting a deep green lawn or lush, green kale, you would use a product with a high first number.

So what would be the reasoning for looking for  a higher second or third number?  To find out, read my blog next month as I explore phosphorus.  Meanwhile, work on memorizing N-P-K along with me, and you will be a tad closer to being a real science type.