Spring is the time for thinking about fertilizers. Organic options are a great way to go - CORVALLIS, Ore
Organic fertilizers such as manures, compost or bone meal are derived directly from plant or animal sources, according to Ross Penhallegon, horticulturist with the Oregon State University Extension Service. Inorganic fertilizers such as ammonium sulfate or ammonium phosphate are often called commercial or synthetic fertilizers because they go through a manufacturing process, although many of them come from naturally occurring mineral deposits.
Inorganic fertilizers usually contain only a few nutrients – generally nitrogen, phosphorus, potassium, sulfur and sometimes micronutrients, either singly or in combination. These nutrients are in a form readily available to plants. However, since they are lost from the soil quickly, you may have to fertilize plants several times during the growing season unless you use a specially formulated, slow-release type.
Some nutrients, such as nitrate, are quickly available for uptake by plant roots, Penhallegon said. If you need only a certain element such as nitrogen and want it to be quickly available to your plants, an inorganic fertilizer such as ammonium nitrate might be in order.
Organic fertilizers usually contain plant nutrients in low concentrations. Many of these nutrients have to be converted into inorganic forms by soil bacteria and fungi before plants can use them, so they typically are more slowly released, especially during cold weather when soil microbes are not as active.
But organic fertilizers have advantages. They don’t make a crust on the soil as inorganic fertilizers sometimes do. They improve water movement into the soil and, in time, add structure to the soil. Organics feed beneficial microbes, making the soil easier to work. But they may cost more than chemical, or inorganic fertilizers, because they are less concentrated, supplying fewer nutrients pound for pound.
Since many chemical/inorganic fertilizers are concentrated and very soluble, it’s easier to apply too much and damage your plants. Fresh, non-composted manure can damage your plants as well, because some manure contains harmful amounts of salts. They can also be a source of weed seeds.
Penhallegon has collected information about the nitrogen (N), phosphorus (P) and potassium (K) content of many of the organic substances commonly used as fertilizer in Oregon. His report, "Values of Organic Fertilizers," also contains information about how quickly an organic fertilizer releases available nutrients and a reference list on organic gardening.
"One of the most difficult things to determine for an organic gardener is how much organic fertilizer to use, say on 1,000 square feet of garden," said Penhallegon. "For a fertilizer with an N-P-K ratio of 12-11-2, this means 12 percent is nitrogen, 11 percent is phosphorus and 2 percent is potassium. In simple terms, this means each 100-pound bag of the fertilizer would contain 12 pounds of nitrogen, 11 pounds phosphorus and two pounds nitrogen.
"For example, using 12-11-2 fertilizer, if we knew we wanted to apply one pound of nitrogen, we would use 1/12th of 100 pounds," he said. "This equals about 8 pounds of this fertilizer applied to get one pound of nitrogen out there in the soil."
Blood meal (12.5-1.5-0.6) releases nutrients over a period of two to six weeks.
Burned eggshells (0-.5-.3), fish emulsion (5-1-1) and urea (urine) (46-0-0) are the fastest-acting organic fertilizers, lasting only a couple of weeks.
To boost the nitrogen content of your soils, apply nitrogen-rich urea (42-46 percent N), feathers (15 percent N), blood meal (12.5 percent N), dried blood (12 percent N).
Organic amendments highest in phosphorus include rock phosphate (20-33 percent P), bone meal (15-27 percent P) and colloidal phosphate (17-25 percent P). High in potassium are kelp (4-13 percent K), wood ash (3-7 percent K), granite meal (3-6 percent K) and greensand (5 percent K).
To make soil less acidic, gardeners want materials rich in calcium, including clamshells, oyster shells, wood ashes, dolomite and gypsum (all are at least 30 percent calcium carbonate or straight calcium).
Many garden centers and feed stores carry organic fertilizers and amendments for gardens.
- Ross Penhallegon
For the gardener new to the idea of organics, the array of options often made available can be confusing. There are dozens of organic fertilizers available, each with different characteristics and not all having convenient labels with simple how-to information to go with them. Those used to exacting recipes and step-by-step measurements and instructions are often bewildered by the apparently willy-nilly “shovel it on” methods of experienced gardeners.
The beauty is, gardening is not an exact science where beakers of measured fluids and charts of soil characteristics and plant viability are the norm. Instead, it’s an “artful science” in which intuition and “feel” have as much to do with it as knowledge and fact. Understanding the common organic fertilizers available is as simple as knowing what each offers your soil and how “available” (easily accessed) those offerings are.
To that end, here’s a quick list of common organic fertilizers and what they offer. Nitrogen (N), Phosphate (P), and Potash (K, potassium) percentages are by weight and “availability” is measured as immediate (fast release, available within hours), moderate (moderate release, available within a few days), and slow (slow release, available in weeks). We’ll include other notes about effects the fertilizer may have on soil pH (acidity) and extra “bonus” nutrients the fertilizer is known for. Your local gardening store may not have some of these organic fertilizers, so try an online retailer that specializes in organic gardening.
Don’t miss our top three favorites from this list of organic fertilizers at the end of the article!
2.5% N, 1% P, 1.5% K
Slow to moderate
Best known as a “hay” for animals, meal is just ground up alfalfa that makes it compost faster in the soil. Best tilled in as an early spring additive, well before planting.
8% N, 6% P, 1% K
Moderate to immediate
The most common source of guano, bat guano is relatively fast in uptake and so is often used between crop rotations (mid-summer harvest / replant) or in late spring just before planting. Bird guano has higher nutrition numbers, but sea bird guano is only available in a few parts of the world.
9% N, 0% P, 0% K
This is a great additive when nitrogen levels are low and leafy plants need a good boost. It is slightly acidic, so some plants may not tolerate it as well as others.
COTTON SEED MEAL:
6% N, 3% P, 1% K
A common fertilizer in areas where cotton is grown, this is a favored year-end, pre-winter mix. Adding it to the soil before cover crops or mulch are put on gives a rich nitrogenated soil in the spring.
CORN GLUTEN MEAL:
0.5% N, 0.5% P, 1% K
Another common late-season, winter preparation additive, corn gluten is a good soil stabilizer for winter.
1% N, 2% P, 5% K
Also a great source for zinc and iron, seaweed is one of the most beneficial organic fertilizers that is freely available on the coasts. Cereal grains and other high-potash crops can especially benefit from seaweed.
2.5% N, 1% P, 1.5% K
Probably the most common organic fertilizer in use in the western world, cow manure is comparable to good compost in nutrient value and uptake. It may contain weed seeds, but is otherwise a gardener’s best friend. Avoid manure from dairies and other industries where the cattle receive a lot of salt.
CHICKEN MANURE (POULTRY):
3.5% N, 1.5% P, 1.5% K
Similar to cow manure, poultry manure is often used in agriculture when organic growing needs a quick boost. Most often, poultry manure is added after harvest and before a second planting.
1% N, 1% P, 5% K
Literally ground up green limestone, it’s a shallow marine sediment and thus full of the richness that the lakes and oceans can offer. The amount of nutrient depends heavily on the source of the sand.
2% N, 1.5% P, 1.5% K
Compost’s actual contents are highly variable and dependent on what was used to make them. Most good compost is a roughly even mix of the big three and can be somewhat alkaline to the soil. Often added before planting, in-between plantings, or at the end of the season. Rough compost can also be used as a beneficial mulch. Also, try worm composting and making compost tea.
3% N, 0.5% P, 2.5% K
Uptake will depend heavily on conditions, but in general, soybean meal is a good additive for longer-lasting results during soil maintenance.
12% N, 1.5% P, 0.5% K
While acidic, blood meal is a very fast “booster” for nitrogen-hungry plants or plants suffering from deprivation. Is most often poured directly over their roots and then covered in mulch.
4% N, 20% P, 0% K
This is most often used in soils requiring serious amendment to bring them up to par. Soils that routinely show high amounts of nitrogen or that produce nitrogen-burnt plants benefit from bone meal.
12% N, 0% P, 0% K
Another nitrogen booster, this is most often used pre-season, before planting, to “pump up the soil” before plants go into it.
10% N, 5% P, 4% K
A fast uptake for a balanced boost of all nutrients is had with fish meal. There’s a reason Native Americans planted a fish at the base of their corn plants in popular legend.
OUR TOP THREE PICKS FROM THE LIST OF COMMON ORGANIC FERTILIZERS
Overwhelmed because there are too many choices? Don’t fret. We’ll narrow it down to just three good, basic choices.
Compost is our first pick because of the unbelievable difference it makes in overall soil health and soil qualities. The bonus is the nutrients that are added to the soil. Also, compost is accessible to everyone. Urban gardeners can compost on their kitchen counter or put a worm bin in their entryway. If you have a small yard, there are a ton of composters available that are easy to use, and some can make their own. Gardeners have been making composters from pallets long before Pinterest came along.
We are going to lump cow and chicken manure together, because we love both and feel both need to be included for different reasons. Cow manure makes for a great overall organic fertilizer and is easy to mix in the top few inches of soil when planting. It is also easy to incorporate in large gardening spaces. Chicken manure gives that pop of fertilizer to the plants and is more concentrated. A little chicken manure goes a long way.
Make sure you are careful when adding manure to the garden. If you age and compost cow and chicken manure on your own, be prepared for a ton of weeds. It is almost worth purchasing from a gardening store, but is easy to find. There are also organic cow manures readily available if you want to take it another step further.
3. FISH MEAL
This is another one of our favorites because it is so easy to use and very versatile. Find a plant that does not respond well to fish emulsion and it may not be worth growing. This one organic fertilizer serves well in the vegetable and flower garden, and is just as beneficial for container plants.
Try using all three of these organic fertilizers for optimal soil and plant health! Mix compost in your soil, add manure when planting, and finish it off and maintain nutrients with fish emulsion every few weeks.