All plants need certain nutrients. There are 16 essential elements for plant growth. The primary elements are nitrogen, phosphorous, and potassium. When you look at a fertilizer bag and see three numbers, those three numbers relate to those three macronutrients, in that order. All of the other 13 elements are called micronutrients. These 13 are very important also, just needed in smaller amounts.
The three macronutrients, which I will refer to as N-P-K, are placed on a fertilizer bag by percentage of weight. For instance, if a bag said 10-10-10 and the bag weighed 100 pounds, there would be 10 pounds of N, 10 pounds of P and 10 pounds of K in that bag. Are you wondering what the other 70 pounds consist of? The other 70 pounds consist of needed fillers and carriers. These make the fertilizer easier to spread and prevent the plants from getting burned from the fertilizer.
There are many different types of fertilizers on the market. Sometimes you will find some that are packaged for certain uses or types of plants. You can find fertilizer specifically for roses, or just for azaleas etc. You will also find that different brands have different nutrient ratios for the same type of plant such as the rose. Other fertilizers say they will increase blooms. There is no guarantee to this. There are lots of factors involved including the type of soil you have.
To find out what type of soil you have, whether it is more acid or more alkaline or neutral, you have to perform a soil test. There are soil test kits you can buy to do this. Fertilizer is not cheap, so doing a soil test will help you get a better start. Every location in an area can be different. Follow the directions for the soil test exactly to get an accurate reading.
Slow release fertilizers give plants an ongoing application of food. This is good for the plant. These slow release fertilizers are released at different lengths of time depending on what type you get. Release rates depend on the fertilizer having a coating and how thick the coating is.
Slow release fertilizers are good for house plants. Care needs to be taken for certain plants such as trees, because the slow release fertilizer will keep them growing too long out of season. One advantage to slow release fertilizers is that they don’t have to be applied very often, but a disadvantage is they are fairly expensive.
Organic fertilizers condition the soil and is relatively a slow release fertilizer. You can buy manure or sewer sludge that has been composted. Depending on the type of manure will determine the amount of nutrients you get. Certain manures burn plants easier also, so be sure they are composted first.
Rabbit manure and chicken manure are good fertilizers as well as others. Sewer sludge is usually 1-2-0 and is mainly a soil amendment. Chicken manure is on the average of 3-5-2. Dairy manure is 2-1-3. So you can see that manures are relatively low in nutrients. Salt may be a problem with manures. Also weed seeds can be a problem. A good thing to do with manures is to compost them at a high heat and then use them.
When buying fertilizer follow the directions on the bag. If you use what you have available be sure you know if it is acid or alkaline. For instance, many people use wood ashes on their gardens. Wood ashes are very alkaline, so if you have alkaline soil already, you don’t want to add wood ashes. If your soil is more acid then you can add them to more neutralize your soil.
Bat guano is used from caves. It’s nutrients are about 6-9-3 and is already partially decomposed. Raw bone meal is 4-22-0 but most of the phosphorous is not soluble. This makes the nitrogen the main value to bone meal. There are many other types of fertilizers, so choose what is best for your soil.
When the weather is hot and dry do not use high nitrogen fertilizers. After applying any fertilizer you should water. Otherwise they will have a tendency to burn. Salts will build up, especially in container plants. Be sure and leach the container plants about every 4 months or so. You can see the salt buildup on the outside of clay pots.
Sometimes when you buy a plant from a nursery the salts are at a higher concentration, but the lighting and drainage are good there and they get constant attention. At home, the plant will not be able to tolerate that much salt. Fertilizer is a salt. Greenhouses feed their plants daily with diluted fertilizer. At home, you won’t be doing this. When you buy a plant from a greenhouse nursery, be sure and leach it out the first time you water it.
What type of soil do you have? This is one thing that is a factor in knowing when to fertilize and how often to fertilize. Also the types of plants being grown will be a factor. Root crops don’t require as much nitrogen as leafy crops. Trees and shrubs feed light and corn is a heavy feeder of nitrogen. Turf grasses are like corn and require lots of nitrogen.
GOOD RULE OF THUMB
Roots and fruit=phosphorous
There are different application methods. You can broadcast fertilizer, such as you do seed over a large area like a lawn. You can do banding which is applying a circle of fertilizer around and deeper than the seed.
Banding is done when transplanting and as the roots develop. The plant has instant access to the food. Starter solutions are used for transplants also. Starter solutions come in liquid form and you should follow the directions on the container.
Side dressing is done after the seeds have come up. Place some fertilizer alongside the plants (about 6-8 inches away) and mix in with the soil. Foliar feeding is a good way to get absorption within minutes of application.
When the soil is still too cold for the microorganisms to convert the nutrients into available forms, use foliar feeding. It is not a substitute for other fertilizers, just a good supplement.