This past winter, the local Home Depot had some screaming deals on fertilizer, most of them being about 90% off. With the way everything is going, I figured it would be a good idea to stock up. But just to be sure, I consulted Blueberry Girl, who is now about five weeks away from earning a bachelor’s degree in soil science. Surely azalea and rhododendron fertilizer (4-3-4) could be used on other plants, right? I seemed to recall that those flowering shrubs liked acidic soil, and so do blueberries. But I needed her confirmation on that. (Even if I could research on my phone, I just didn’t have time to do it.)
Yep, she said, buy it all. At a buck for an eight-pound bag, it was a no-brainer (at least, for Blueberry Girl it was).
I didn’t have to ask her about the other options. Fish emulsion (5-1-1) and another formulation (3-3-0.3) at a dollar per quart (I think I got 22 quarts total) and several bags of Dr. Earth Organic Fertilizer (2-2-2) for a dollar (fish emulsions) or two (the organic bags) were easy decisions. I could do the research on exactly how to use them later.
It’s now later for me, but how does this apply to everyone else?
With all the supply chain issues, and with the increasing need for raising more of our own food, we may not have the fertilizer options we’ve grown accustomed to. We might come across deeply discounted products we wouldn’t normally use at nurseries or grocery stores, or even garage sales. We need to know how to use the various products and what their shelf life is. (Did you know fertilizers have a shelf life? Me neither.)
Before applying any fertilizer, have a soil test conducted through your county extension office. Because plants deplete soil as they grow, these tests need to be performed every 2-3 years. Unfortunately, we likely will not have access to extension offices or private testing firms post-collapse. In this case, compost and/or slow-release fertilizers will be a better choice since they will be less likely to harm plants. And we’ll also need to learn how to identify and rectify problems on our own.
All packages of fertilizer list the nitrogen-phosphorus-potassium (hereafter, NPK) ratios, usually rather boldly on the front of the package. These are the big three nutrients that are added to the soil to feed plants. They are always listed in this standardized format in alphabetical order (nitrogen, phosphorus, and potassium—which is designated by a K, from kalium, which is Latin for potassium). This series of numbers indicates the ratio, or percentage, of nutrients by weight. So, the higher the number, the more concentrated the nutrient is in the fertilizer. 10-10-10 has twice as much fertilizer per pound as 5-5-5. Synthetic fertilizers have higher numbers than organic fertilizers.
Now let’s take a look at each of the individual components, what they do, and how to identify problems.
· Nitrogen is essential to the growth of strong foliage—it makes plants greener. It’s why lawn fertilizers have ratios like 20-2-6. Evergreens need high nitrogen to keep them green, something like 30-10-10. (They also need copper, iron, and molybdenum.) As far as garden crops go, leafy vegetables require more nitrogen. Nitrogen comprises 78% of the air we breathe, but atmospheric nitrogen is not available to plants. They have to get it from the soil. A natural way to put nitrogen into the soil is through planting nitrogen fixers like peas, beans, and other legumes. It’s one reason why practicing good crop rotation will become increasingly important in the home garden. Organic sources of nitrogen include blood meal, feather meal, and fish fertilizer.
o Nitrogen deficiencies are manifested by the yellowing of older leaves and slowing or stopping of growth.
o Nitrogen excesses are indicated by fast growth and spindly, weak, dark green leaves.
· Phosphorus contributes to the growth of strong roots and flowers, including blossoms and fruit production. Something like 5-10-10 makes for good weekly or bi-weekly feeding for tomatoes, and the same goes for flowering annuals, which bloom profusely when nitrogen is restricted. Last year, I planted hundreds of pansies, which had fairly lush green growth. Many of those pansies reseeded themselves this year. However, on a lot of those plants, one can barely see any leaves amidst the profusion of flowers. This suggests to me that the nitrogen in the soil is low—and I better get some added to the soil around those flowers if I want the vegetables to produce. Plants consume more phosphorus during blooming and seed setting. Keep in mind that phosphorus becomes unavailable to plants if the pH is off balance. Also, phosphorus does not leach out of the soil, so levels can build up and become too high.
o Phosphorus deficiencies can be recognized by dull green, sometimes yellowing, leaves and purplish stems, or by a lack of lush green growth and blooms.
o Excessive phosphorus will bind iron and zinc, making these nutrients unavailable to plants (evidenced by yellowing and withering of the plants). Unfortunately, little can be done to remove excessive phosphorus from the soil. It will be important to avoid adding phosphorus to the soil for several seasons to help lower phosphorus levels. Growing nitrogen-fixing plants like peas and beans in areas with excessive phosphorus will increase the amount of nitrogen in the soil without resorting to added fertilizers (including organic fertilizers and compost) and will hasten a return to normal nutrient levels.
§ Iron deficiencies are exhibited by a yellowing of younger leaves with the veins remaining green.
§ Zinc deficiencies manifest in early spring as dwarfing of the plants and have yellow striping between the veins of younger leaves.[1]
§ Both of these deficiencies may occur at the same time and make it difficult to determine the actual problem.[2]
· Potassium (also called potash) contributes to overall vigor and good fruit production. It helps the plant fight off disease and withstand extreme temperatures to adapt to harsh conditions. Most soils have sufficient potassium, so this number tends to be lower.
o Potassium deficiencies are indicated by the yellowing of older plant leaves along the edges or between the veins, and the leaves may die at the edges or tips. Plants will wilt more easily in hot weather and succumb to pests and disease more quickly. Treat deficiencies by making sure the soil is watered well, well-drained (but don’t let it dry out), and aerated. If it’s early in the season, use cloches or wall of waters to warm the soil and thus improve the plant’s ability to uptake potassium. If all else fails, organic sources of potassium include wood ash (this will also raise the pH), kelp, and banana peels.
o Potassium excess itself rarely
affect plants, but excessive potassium can cause deficiencies of other
nutrients.
Links to related posts:
DIY
Complete Organic Fertilizer
Crop Rotation for Maximum Yields
Synthetic Fertilizers, Pesticides, and Herbicides
References:
https://www.thespruce.com/best-fertilizers-4154249
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-npk.htm
