The ABCs of NPK
First for me was ABCs, then BVDs. Next, in my first at bat in little league, it was HBP (squarely on left rump). Later it was that LP by CS&N, but eventually, after my BA, I took up gardening and learned about NPK which stands for nitrogen, phosphorus and potassium.
Gardeners can get better results from their efforts if they learn a tiny bit of chemistry. Your vegetables and flowers are counting on it, so here is a kindergarten-level guide to garden chemistry.
Printed on packages of soil amendments and fertilizers are three numbers which indicate the ratio of nitrogen to phosphorus to potassium, or the NPK numbers. The reason for these numbers is the different elements have different benefits for plants. Nitrogen is what plants need for leaf growth. The air we breathe is about 78 percent nitrogen, but it is not available to plants so they must get it from soil.
Chlorophyll, the green pigment in plants, is mostly nitrogen and it is responsible for photosynthesis. Leafy plants such as lettuce, bok choi, kale and chicory benefit from a healthy dose of nitrogen. A time-honored source of nitrogen is horse, cow, rabbit or poultry manure. Fish emulsions are also excellent sources as is cottonseed meal and feather meal. Literature says blood meal is a reliable source of nitrogen, but I choose not to spread dried blood powder around my tat soi. I’m staying with horse poop.
Phosphorus has the chemical symbol P, and it is important for healthy roots and for moving nutrients through the stems for flower and fruit production. Lack of phosphorus means growth slows to a halt because cells fail to replicate, but the good news is decomposition of organic matter makes it available for roots to absorb. Purplish leaves or seemingly healthy plants with plenty of foliage but no blooms are indicators your plants are calling for phosphorus.
Sources of phosphorus, if you need it, are rock phosphate or bone meal. Seaweed emulsions add not only phosphorus but an array of other important trace elements. However, keeping your garden beds covered with organic material is an easy long-term answer for supplying phosphorus.
Potassium, often known as potash, has the chemical symbol K because the medieval Latin name for potash was kalium. It is essential for strong stem growth, carbohydrate transferal, disease resistance and healthy fruit.
If the soil lacks enough potassium, plants look sickly, fruit do not fully develop, and the plants suffer more during stressful weather such as drought.
The best sources of potassium are compost, wood ashes, kelp meal, greensand, alfalfa hay and granite dust.
So, if you see 10-6-4 on a soil amendment bag, you would be getting more nitrogen but a moderate proportion of phosphorus and a slightly lesser amount of potassium – maybe for broccoli or brussels sprouts. Tomatoes would appreciate less nitrogen and more phosphorus, and I’ve seen ratios for tomatoes in the range of 8-32-16 or 6-24-24.
However, potato growers who study chemistry late at night might apply a heavy nitrogen regimen until the final month of growth and then switch to more potassium in the ratio of 14-7-21. You can see garden chemistry can get esoteric and idiosyncratic.
Also, NPK are not the only alphabets your garden needs. Calcium, Ca on your periodic table, aids in the manufacture of plant cells, promotes healthy root development and improves soil structure. Dolomite and bone meal are good sources of calcium if you need it.
Dolomite also adds magnesium to the soil, and you might not need much. Magnesium sulfate, MgSO4, known as Epsom salts, is used by some gardeners as a midseason additive for tomatoes and peppers to make them sweeter.
Other elements also matter, but regular doses of mulch and manure might be all your garden needs to pass its chemistry test. Easy as ABC.