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Step 5Fertilizer
If your plant is actually growing, it will eventually need fertilizer. It is hard to judge whether your plant needs fertilizer or not, but there are certain things that remain constant.
For the most part, your plant won't need as much fertilizer (if any) during the winter months, as the temperature indoors is most likely cooler, and the light source isn't as bright. Cooler temperatures and dimmer light sources lead to slower growth rates. Plant don't need as much nutrients when their growth has slowed down to a crawl.
There are 17+ elements that are utilized in the plant- 17+ elements that are required for normal growth and development.
89% of a plant's weight is made out of elements supplied by water and C02.
The other 11% of a plant's weight is supplied by elements supplied by fertilizer, organic matter, or elements already in the soil....
There is almost always a set of three numbers written on any fertilizer package. The first number is the % nitrogen in the fertilizer. The second number is % P205 (A compound containing Phosphorous) in the fertilizer. The third number is the % K20 (a compound containing Potassium) in the fertilizer. Nitrogen, phosphorous, and potassium are 3 macronutrients (elements needed in high quantities by the plant). Nitrogen and potassium are needed in much larger quantities than phosphorous. Urea (urine contains urea, but also contains other things...) and ammonium are sources of nitrogen, but can injure your plants. Nitrates will not burn your plants as easily. Ammonium is used in fertilizers because it is held by the soil. Nitrates are more easily leached out. There are benefits and downfalls of each form nitrogen commonly used in fertilizers.
The other three elements that are needed in large quantities (besides carbon, oxygen, and hydrogen) are magnesium, calcium, and sulfur. These may or may not be supplied by the fertilizer. It is generally good to use a fertilizer containing these three elements as well (don't look to hard....) Epsom salts found at almost every grocery or drug store will supply magnesium and sulfur.
There are also a a few more elements needed for normal plant growth that are often left out of fertilizers. These elements are needed in fairly small quantities ( called micronutrients for this reason- not size of the element...). Foliar applied (applied to the leaves) fertilizers contain micronutrients. So certain elements can be applied directly to the leaves if one chooses to do so.
If you really want to know, the micro nutrients a plant needs are iron, manganese, boron, Chlorine, zinc, molybdenum, nickel, and apparently cobalt as well.
You can technically stick an iron nail into the soil as a source of iron, but it won't work very well. Micronutrients need to be treated before they can be readily taken up by the plant. I wouldn't recommend trying to do this yourself, so just let the fertilizer manufactures do it for you. Fertilizers that contain micronutrients will be treated so you don't have to worry about it.
Fertilizers are sold either as slow-release fertilizers, or quick-release fertilizers.
Slow release fertilizers are generally coated in a material of varying thickness that breaks down over time to release the tiny fertilizer pellets inside over a period of a few months. Slow-release fertilizers are generally mixed into the potting soil/medium at planting time, but they can also be spread onto the top of the soil at any time. Slow release fertilizers take the guess work out of fertilizing- just follow the directions, and your plant will be fed worry-free for a while.
Quick-release fertilizers are water soluble fertilizers that are immediately available to the plant. These fertilizers can easily damage the plant if over-applied. If you are unsure of how much fertilizer to use, it is better to apply a weak fertilizer solution than one that is too strong. If one chooses to use quick-release fertilizers I would recommend diluting the fertilizer and adding the diluted fertilizer to the water normally used to water the plant- fertilizing the plant every time it is watered. This is called fertigation (fertilization plus irrigation...). If diluted correctly, the plant will receive roughly the same amount recommended on the package, but slowly, and not all at once. Fertigation will reduce the risk of harming the plant, while giving the plant what it needs, as it needs it- similar to slow-release fertilizers.
Organic matter- the alternative to commercial fertilizer
There is one way you can easily supply all the elements (besides the input of CO2 and water) a plant will need to grow. Compost or grind up plant scraps, weeds, or lawn clippings. These plants gathered all the necessary nutrients in the correct quantities for you!!!
Do not use plants as fertilizer that have been sprayed with herbicides. They may still contain residues of these herbicides, leading to the death of anything you that you fertilize with these herbicide-sprayed plants.
You may have heard and or bought the fancy organic fertilizers that contain kelp or seaweed. Well, if you live anywhere near the water, pick your own- it's free! Wash the plants off though, especially if they grew in salt water. If there are any cottage owners or owners of waterfront property that have problems with stinky seaweed sludge washing ashore, it should be a great fertilizer once properly rinsed out. The salts from the sea water will be harmful to your plants- salting the land acts like an all purpose, and rather permanent herbicide. A word of warning- Freshwater seaweed sludge may contain toxic chemicals such as PCB's. You might not want to apply a form of this sludge to plants you will be eating....
The cooled water left over from cooking vegetables is also a safe source of a number of different nutrients. Water the plants as you would otherwise.
The ph of the soil/potting medium will determine the availability of the various elements ( supplied by the fertilizer).
I you actually have a ph tester lying around (I currently do not, so I don't blame you) you can test the soil to see if the ph is within the correct range. If the mix is way to acidic or basic, your plant might be getting to much of a certain element, and not enough of another....
Soil based potting mixes should have a pH between 6.2 and 6.8.
Soilless potting mixes should have a pH between 5.4 and 6.5.
Adding lime (not the fruit) will raise the pH of the potting medium. Adding acids (either nitric, sulfuric, or phosphoric) will lower the pH.
The pH of the potting soil/medium being used is generally not a problem, but it might just be the reason why a plant looks sickly.
In response to a comment below, soil and or potting medium cannot hold every bit of fertilizer that is thrown at it....
For the most part, your plant won't need as much fertilizer (if any) during the winter months, as the temperature indoors is most likely cooler, and the light source isn't as bright. Cooler temperatures and dimmer light sources lead to slower growth rates. Plant don't need as much nutrients when their growth has slowed down to a crawl.
There are 17+ elements that are utilized in the plant- 17+ elements that are required for normal growth and development.
89% of a plant's weight is made out of elements supplied by water and C02.
The other 11% of a plant's weight is supplied by elements supplied by fertilizer, organic matter, or elements already in the soil....
There is almost always a set of three numbers written on any fertilizer package. The first number is the % nitrogen in the fertilizer. The second number is % P205 (A compound containing Phosphorous) in the fertilizer. The third number is the % K20 (a compound containing Potassium) in the fertilizer. Nitrogen, phosphorous, and potassium are 3 macronutrients (elements needed in high quantities by the plant). Nitrogen and potassium are needed in much larger quantities than phosphorous. Urea (urine contains urea, but also contains other things...) and ammonium are sources of nitrogen, but can injure your plants. Nitrates will not burn your plants as easily. Ammonium is used in fertilizers because it is held by the soil. Nitrates are more easily leached out. There are benefits and downfalls of each form nitrogen commonly used in fertilizers.
The other three elements that are needed in large quantities (besides carbon, oxygen, and hydrogen) are magnesium, calcium, and sulfur. These may or may not be supplied by the fertilizer. It is generally good to use a fertilizer containing these three elements as well (don't look to hard....) Epsom salts found at almost every grocery or drug store will supply magnesium and sulfur.
There are also a a few more elements needed for normal plant growth that are often left out of fertilizers. These elements are needed in fairly small quantities ( called micronutrients for this reason- not size of the element...). Foliar applied (applied to the leaves) fertilizers contain micronutrients. So certain elements can be applied directly to the leaves if one chooses to do so.
If you really want to know, the micro nutrients a plant needs are iron, manganese, boron, Chlorine, zinc, molybdenum, nickel, and apparently cobalt as well.
You can technically stick an iron nail into the soil as a source of iron, but it won't work very well. Micronutrients need to be treated before they can be readily taken up by the plant. I wouldn't recommend trying to do this yourself, so just let the fertilizer manufactures do it for you. Fertilizers that contain micronutrients will be treated so you don't have to worry about it.
Fertilizers are sold either as slow-release fertilizers, or quick-release fertilizers.
Slow release fertilizers are generally coated in a material of varying thickness that breaks down over time to release the tiny fertilizer pellets inside over a period of a few months. Slow-release fertilizers are generally mixed into the potting soil/medium at planting time, but they can also be spread onto the top of the soil at any time. Slow release fertilizers take the guess work out of fertilizing- just follow the directions, and your plant will be fed worry-free for a while.
Quick-release fertilizers are water soluble fertilizers that are immediately available to the plant. These fertilizers can easily damage the plant if over-applied. If you are unsure of how much fertilizer to use, it is better to apply a weak fertilizer solution than one that is too strong. If one chooses to use quick-release fertilizers I would recommend diluting the fertilizer and adding the diluted fertilizer to the water normally used to water the plant- fertilizing the plant every time it is watered. This is called fertigation (fertilization plus irrigation...). If diluted correctly, the plant will receive roughly the same amount recommended on the package, but slowly, and not all at once. Fertigation will reduce the risk of harming the plant, while giving the plant what it needs, as it needs it- similar to slow-release fertilizers.
Organic matter- the alternative to commercial fertilizer
There is one way you can easily supply all the elements (besides the input of CO2 and water) a plant will need to grow. Compost or grind up plant scraps, weeds, or lawn clippings. These plants gathered all the necessary nutrients in the correct quantities for you!!!
Do not use plants as fertilizer that have been sprayed with herbicides. They may still contain residues of these herbicides, leading to the death of anything you that you fertilize with these herbicide-sprayed plants.
You may have heard and or bought the fancy organic fertilizers that contain kelp or seaweed. Well, if you live anywhere near the water, pick your own- it's free! Wash the plants off though, especially if they grew in salt water. If there are any cottage owners or owners of waterfront property that have problems with stinky seaweed sludge washing ashore, it should be a great fertilizer once properly rinsed out. The salts from the sea water will be harmful to your plants- salting the land acts like an all purpose, and rather permanent herbicide. A word of warning- Freshwater seaweed sludge may contain toxic chemicals such as PCB's. You might not want to apply a form of this sludge to plants you will be eating....
The cooled water left over from cooking vegetables is also a safe source of a number of different nutrients. Water the plants as you would otherwise.
The ph of the soil/potting medium will determine the availability of the various elements ( supplied by the fertilizer).
I you actually have a ph tester lying around (I currently do not, so I don't blame you) you can test the soil to see if the ph is within the correct range. If the mix is way to acidic or basic, your plant might be getting to much of a certain element, and not enough of another....
Soil based potting mixes should have a pH between 6.2 and 6.8.
Soilless potting mixes should have a pH between 5.4 and 6.5.
Adding lime (not the fruit) will raise the pH of the potting medium. Adding acids (either nitric, sulfuric, or phosphoric) will lower the pH.
The pH of the potting soil/medium being used is generally not a problem, but it might just be the reason why a plant looks sickly.
In response to a comment below, soil and or potting medium cannot hold every bit of fertilizer that is thrown at it....
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Mar 11, 2009. 2:39 AMpr1mus285
says:
Don't forget to watch Ph and add lime / sulfur as necessary! Also, remember, apply the fertilizer to the roots, not the leaves! also, the typical potting soil has a very high CEC, so every bit of fertilizer you apply will be sucked up by the soil and held for later use (the plants bump off cations on the CEC they need by putting out into the soil other cations). You don't need to apply fertilizer that often for this reason.
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Mar 20, 2009. 7:38 AMBubbleDragon
says:
I'm not sure I buy this. The "extra" fertilizer might be sucked up by the soil, but it'll be held there burning the plant's delicate root system like a salt - ever see a chalky build up on the rim of a clay pot? It's safe to say you can cut the recommended fertilizer amount (given on the bottle) by 1/2 or 1/4 and probably have healthier plants, though I suppose your argument for fertilizing less often would have a similar end result. Also, some fertilizers CAN be applied to the leaves, such as fish emulsion.
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