Fertilizers

Fertilizer  is an incredibly complicated topic. Soil fertility is not as easy as "things grow" or "things don't grow." Just like people, plants need a wide and balanced variety of nutrients. After all, fats, carbohydrates and protein may be the three "basic" nutrients for humans, but a human raised on just these three things wouldn't be as healthy as a human with a varied diet. Humans need "micronutrients" like vitamins  and minerals, and plants need many of the same things! 

While plants make their own basic food by photosynthesis, they still need a number of other nutrients for growth, flowering, fruiting and other life cycle functions. They get carbon and oxygen from the atmosphere but for most other elements they depend on the soil and, by extension, on you.

Furthermore, the soil environment can affect plants in other ways besides the supply of nutrients. Some plants may prefer a more acidic or basic soil, but most prefer a neutral or very slightly acidic pH. If your soil pH is too high or too low, you should add the appropriate material to balance it out. Soil pH can be determined with an easy-to-use soil testing kit.  Soil pH mainly affects how well your plants can absorb nutrients from the soil and which nutrients are available, so it is important to maintain the right balance.  

Plant Nutrition

Just like people, plants need different nutrients in different amounts. Some are readily available from the environment -- air and water provide carbon, oxygen and hydrogen. Everything else comes from the soil and, by extension, from you. This is especially true of houseplants  and container gardens,  which have only a limited amount of soil  to work with, but all of the plants in your garden from crocus to oak tree need many of the same nutrients.   

• Macronutrients
• Nitrogen, phosphorus and potassium (NPK) -- essential for healthy plant growth. They can't grow without them.
• If your soil is low in any of these you should fertilize it.
• Nitrogen  encourages lots of green, leafy growth. Use it around foliage plants but don't put too much near your flowering or fruiting crops.
• Phosphorus  encourages root and flower/fruit growth.
• Potassium  helps root development and disease resistance.
• The macronutrient content of a synthetic fertilizer is always marked on the bag as a series of three numbers in what is known as the N-P-K ratio.
• For example, a 14-10-12 fertilizer contains 14% nitrogen, 10% phosphorus and 12% potassium by weight.
• Secondary Nutrients
• Calcium, sulfur and magnesium are all important. They are needed in smaller quantities than the NPK trio.
• Magnesium is important to the synthesis of chlorophyll, the green pigment plants use to absorb the sun's energy.
• Micronutrients
• Just like us, plants need a wide variety of elements in small quantities.
• A few of these are boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel and zinc.

Natural (Organic) Fertilizers

There are many kinds of natural fertilizers,  These can be divided into three main categories: animal, vegetable and mineral. In this context, "organic" refers to "from natural sources/approved for organic farming and gardening." Note that "organic" fertilizers can be entirely composed of inorganic materials. 

Animal Byproducts

Most animal product fertilizers are by-products from the meat, egg and dairy industries. If you are adamant about having an organic and vegan garden, skip this section and read up on plant-based fertilizers. Keep in mind, however, that these fertilizers are made from parts of the animal that would otherwise be wasted anyway, so animal-based fertilizer doesn't necessarily contribute further to the meat industry. 

• Manure
• There are two main kinds of manure: "hot" and "cold."
• Hot manure  (from horses, pigs, chickens, etc.) is extremely nitrogen-rich. It is called hot because the high levels of nitrogen can burn your plants. Hot manure needs to be composted before it is applied to your plants.
• Cold manures  (from cows, sheep, goats, other ruminants, rabbits, etc.) have less nitrogen and can be applied directly to the soil as an amendment.
• Composted manures don't smell bad.
• Guano is the collected droppings of seabirds or bats. It is particularly high in nitrogen and phosphorus.
• Blood Meal
• Steamed, dried blood from the meatpacking industry.
• Rich in phosphorous.
• Bone Meal
• Ground bones from the meatpacking industry.
• Good source of phosphorus; also adds calcium. Particularly recommended for roses.
• Fish Emulsion
• A liquid byproduct of the fish industry.
• Very mild, good for young plants.
• Smells fishy.
• Feather Meal
• Ground-up feathers from the poultry industry.
• Primarily a source of nitrogen.
• Urine
• Rich in nitrogen.

Plant-Based Fertilizers

• Compost
• Adding compost  is just about the best thing you can do for your soil no matter what.
• Compost  adds organic material back to the soil, which improves the texture and drainage.
• It also adds nutrients and won't burn your plants.
• You might still need to supplement your compost if your soil is very deficient in one or more nutrients or has a pH imbalance.
• You can also apply compost tea,  a solution of compost in water, and apply it as a liquid fertilizer. You can read more about it on Wikipedia.
• Green Manure
• Green manure  refers to cover crops that are grown for a specific period of time and then plowed into the soil. The plants then decompose, enriching the soil further.
• Green manure crops are often in the legume family; legumes have nitrogen-fixing bacteria in their roots and help add nitrogen to the soil.
• Green manure also helps improve the soil texture by improving water retention and drainage and by preventing erosion during non-growing season.
• A controlled form of allowing fields to lie fallow for a period of time.
• Some popular green manure crops are clover,  oats,  rye,  mustard,  fenugreek  and several kinds of beans. 
• Cottonseed Meal
• Cottonseed meal  is a byproduct from the cotton industry; good source of nitrogen.
• Peat
• Peat  is another kind of partially decomposed vegetable matter.
• May not be the most environmentally friendly choice, as peat bogs have become endangered habitat.
• Seaweed or Seaweed Extract
• If you plan to use raw seaweed you gather yourself, be sure to rinse it off first to keep the salt out of your soil. Also be sure to collect only from unpolluted areas and areas not contaminated by nearby nuclear power plants.
• Seaweed  is also a great addition to compost.
• Most people use processed seaweed or seaweed extract.  It has a wide range of nutrients but is an especially good source of potassium.

Mineral Fertilizers

• Greensand
• Greensand  is a mineral-rich sedimentary rock which is ground up and added to soil.
• Rich in potassium and iron.
• Superphosphate
• "Superphosphate"  is phosphate treated with sulfuric acid to makes it easier for plants to absorb it.
• Powdered Limestone
• Powdered limestone  adds calcium to the soil and neutralizes acidic soils.
• Saltpeter
• Saltpeter  is potassium nitrate -- NPK ratio of 13-0-44.
• Potash
• A mineral found in wood ashes, potash  is a powerfully basic substance and will neutralize acidic soils.
• Good source of potassium.

Synthetic Fertilizers and Plant Food

In the last 100 years, our knowledge of chemistry has given us the power to create precise blends of chemicals in labs. Like any technological leap, synthetic fertilizer has taught us that Spiderman  knows best -- with great power comes great responsibility. Synthetic fertilizers can give great results in your garden but they can also be dangerous to your plants, your family, your pets and the environment when not used according to label usage and safetly instructions. Use caution when using any synthetic fertilizer and take appropriate precautions to protect yourself during applications. Use the absolute minimum for your garden; fertilizer runoff is a major pollutant in the ocean, where it can trigger algal blooms that suffocate other ocean life. 

Synthetic fertilizers have another downside -- the rising costs of oil. The connection may not be immediately obvious, but it does exist. Nitrogen is not an easy element to "fix" -- that is, to render usable by plants. It takes a lot of energy to fix nitrogen, and most of that energy comes from oil. As energy prices continue to rise, fertilizer prices will rise as well. Composting,  however, requires very little energy input from humans; the bacteria and other microorganisms do most of the work. Read up on composters  and backyard composting before buying fertilizer, and save yourself a lot of money in the long run. 

Fertilizer

There are two kinds of fertilizer: liquid  and granular. Granular fertilizers  can be further divided into slow-release  and quick-release. 

Liquid Fertilizer	Granular Fertilizer
Absorbed quickly and fast-acting. Also washes away quickly; requires reapplication every 2 to 3 weeks. Sold as concentrates; need to be diluted before use. Some brands require specialized attachments that hook up to your hose for easy mixing while watering.	Applied dry, needs to be watered to start working. You can see how much is being applied. Applied by hand or with a mechanical spreader. Slow-Release  (aka water-insoluble nitrogen (WIN)) Has a coating to slow release of nutrients. Sulfur-coated lasts about eight weeks. Polymer-coated lasts about 12 weeks. Quick-Release  (aka water-soluble nitrogen (WSN)) Last three to four weeks.

Plant Food

Plant foods  are a type of fertilizer that is usually formed into a small, slow-release tablet  or spike  and is formulated for a specific kind of plant, such as African violets.   They're usually used for houseplants, but some are available for outdoor plants such as roses  or rhododendrons.  These are usually spikes that are inserted into the soil near the roots of the plant. There are a number of blends available; formulas for foliage plants contain lots of nitrogen, while food for flowering plants is heavier in phosphorus.

Plant foods are a good choice for potted plants.  Since potted plants need frequent watering, nutrients are rapidly washed out of the soil. A slow-release food spike  can help mitigate this loss.

External Links

• Lowes.com -- another of Lowe's excellent buying guides; this one will help you choose the right fertilizer. Keep in mind that it leans towards synthetic fertilizers.
• Organicgardening.com -- short article on fertilizing an organic garden. (Hint: it's compost.)
• Allaboutlawns.com -- list of many articles about lawn fertilizer from ChemLawn.
• Lawncare.com -- Whether you are a hobbyist or simply looking for help maintaining a great-looking yard, this site has is loaded with information to help you keep your lawn looking its best.
• Lawn Care for the Beginner -- a collection of resources for the novice from Scotts
• How the Environment Benefits from a well-maintained lawn-- a report on effective turf maintainance from the Lawn Institute