Like anything in this world, excessive amounts of any one thing is often a bad thing, even if that substance is necessary for survival. Just because you think your plant might want more of something, doesn't mean you are doing your plant any good. The fact of the matter is, unless you know what you are doing, you may very well be killing it. Plants can't scream in pain like the rest of us....
Step 1: Try to Figure Out What Your Plant Is Called
These names will only help you find extra information on how to grow each specific plant, and how to correct any problems that may occur.
Step 2: Give It the Light It Needs
Various plants will need various levels of light. They have grown accustomed to differing levels of light through evolution. Plants receive the energy they need to survive from light- Mainly the red, and blue wavelengths of light (the reason why plant lights give off a bluish-purplish light).
Unfortunately, the average home is far darker than the environment outside. When one is out in the middle of a field, he or she can clearly see that light can reach the plants around him no matter what time of day it is. This is not the case inside a home. The various opaque structures of a home keep light from reaching plants inside. Light can't pass through a brick wall....
For those of us in the northern hemisphere, the sun is always to the south. This means that south-facing windows will let the most sunlight into the home. Most plants will appreciate being placed right in front of a window (A south-facing window is best).
It is not just light intensity that matters- the duration of light is also important. Try to give your plants a whole day's worth of sunlight. That being said, if you have no windows facing somewhat-south, you are at a clear disadvantage. You should get them as close to their light source as possible. Interior plants that receive light through a north-facing window may need supplemental light. Turn on a fluorescent light bulb to simulate day time. Get the bulb as close to the plant as possible, without the plant being overheated by it or touching it directly. Using electricity to help keep a plant alive is a completely legitimate reason to keep the light on (but can get expensive if you are paying for electricity).
Plants also need darkness to survive. This is how they have evolved.... Give them at least a couple hours of darkness every night if possible. If you aren't using a room at night, turn the lights off to give the plants some darkness. This is better for the environment anyway. 12-hours light, 12 hours darkness, is a good rule of thumb to follow. One does not have to follow this exactly.
Plants tend to flower and produce fruit when a certain daylength is met, and held constant for a period of time. Each plant will be different. Look up how day length and flowering for your particular plant to see what I mean.
Leaves that develop under any particular lighting condition will contain a particular amount of chlorophyll that will be most beneficial in that light intensity. If a plant is moved from a low-light situation to a high light situation, the leaves that developed under low light will soon become burned, and or bleached out.
On the other hand, if the plant is moved into a darker area, any dark green leaves that developed under high light intensities will be sacrificed by the plant, only to be replaced by leaves better suited for the plants new environment.
A plant must be acclimatized to its new environment. Simply put, ease the plant into any dramatic change in its environment. Increase the light levels gradually, and not all at once.
Step 3: Watering
A good way to accurately and efficiently find out when your plant needs more water is to keep an eye on the soil. When the soil looks dry, just stick you finger in it. If the soil is dry in the first couple centimeters, is it probably time to give the plant more water. If your finger comes up with a little water on it, your plant is probably fine.
I water my plants every Sunday while they are inside, unless they need water earlier. Once I move my plants outside for the summer, they need to be watered much more often.
Try not to water your plants while the sun is shining on them. Any water droplets on the leaves will act like tiny magnifying glasses. If the light hitting the water droplets is strong enough, the leaves may actually be burned.
Some plants like their soil to be continually damp, and some plants like the soil they grow in to dry out a little in between waterings.
How much water do you give it?
Saturate the soil. Pour water into the soil slowly, so that water is moved throughout the soil before exiting the bottom of the pot. If you do this correctly, the soil will be thoroughly and adequately watered by the time water comes out the bottom of the pot. Keep watering (slowly) until a little water comes out the bottom of the pot. A good rule of thumb is about 1/10 of the water you put in should flow out the bottom of the pot. A little plant tray that will keep the access water under control is a very good investment. But any waterproof surface will do.
Water quality is very important!
If you have a lot of dissolved minerals and salts in your water, the soil will eventually accumulate this minerals and salts, and will be injured by them.
Your plant does not necessarily need distilled water, but filtered water can be beneficial if the water it would be receiving is quite hard. If you have very hard water, filter your water at home- do not buy bottled water to water your plants with. Filtering your water at home is FAR cheaper than bottled water, and it is better on the environment as well.
Soft water is also terrible for plants. Soft water is extremely salty water. Water softener salts will injure plants.
Rain water is an excellent source of water for your plants. Any rain that flows off the roof will be fine. A rain barrel is a worthy investment!
Step 4: The Kind of Soil
Potting soil found in bags at the store will suffice for most plants.
You can make your own soil-less potting soil as well. Sphagnum peat moss, coconut coir, perlite, vermiculite, and concrete-grade sand, and bits of pine bark are all good to use as ingredients a potting mix. If you want to make some of your own, you are going to want to buy the ingredients in bulk, as it is a lot cheaper than way.
A few recipes include:
1 part Sphagnum peat moss, 1 part vermiculite
1 part coconut coir, 1 part sphagnum peat moss, 1/2 part perlite, and 1/2 part vermiculite
3 parts pine bark, 1 part sand, and 1 part sphagnum peat moss
One that includes soil as well is 1 part soil, 1 part sand, and one part sphagnum peat moss.
Each one of these formulations provide different growing conditions for your plant.
Dry sphagnum peat moss is notoriously difficult to get wet. To combat this problem, just put the sphagnum peat moss, or sphagnum peat moss containing mix in a water-proof container with some water. Shake the container around a while. Warm water will speed up the process.
You can also microwave the container as long as the container is glass, or recyclable number 5. The steam will quickly infiltrate the moss. Just remember to let the mix cool before you put a plant in it.
The soil provides the plant with support, while giving it access to adequate amounts of air, water, and nutrients.
Aeroponics, and hydroponics take advantage of this, and supply the plants with the necessary support, air, water, and nutrients without using any soil, or soil-less medium at all. It is quite interesting....
Step 5: Fertilizer
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....
Step 6: Potting/repotting
If you want to check if they do or not, gently slip/shake/wiggle the plant out of pot (soil still on roots). If the roots are rapping around the pot, it is most likely time to repot. If the pot is literally deformed by the roots, it is also time to repot.
Roots have little single-celled hairs that grow on them. These are called root hairs. The root hairs suck up most of the water and nutrients that the plant needs. They are extremely delicate. Disturb the roots as little as you can. Trying to find these root hairs will most likely rip them all off- don't do this....
Choose a pot that is slightly large than the original root ball or pot. Do not double the size of the pot each time you repot, as most potted plants do not like this. Plants react differently when they are potted as compared to outside in the soil.
A good pot must have drainage holes. The size of the drainage hole/s isn't really all that important of an issue. As long as the pot has a whole that is large enough to let access water exit, without vast amounts of potting soil fall out with it.
Always wet the potting soil before you add the plant to it, and as well as after the plant is potted up again. This will reduce the shock of having some root hairs ripped off during the potting process.
The original soil surface should remain the soil surface after repotting. Do not bury the plant any further down than it was originally- keep it level with the original soil surface.
Placing a little soil on the bottom of the pot before placing the plant into it's new container is always a good idea. Make sure the soil in the pot and the bottom of the soil/root ball make good contact. Large air bubbles in the soil should be avoided.
Also, do not fill the entire pot full to the brim with soil/plant. Leaving a little space will make it easier to water the plant (less overflow).
Tall pots drain better than short pots. This is due to gravity, and the weight of the water on itself. Try holding a wet sponge vertically as compared to horizontally if you don't believe me.
Anything semi-rigid to rigid will do for a pot, keeping in mind the depth of the container. All the pot needs is a few small holes in the bottom. Try digging through the recycling. If you happen to come across a landscaping crew installing plants, ask if you can have any of their empty pots. Sometimes landscaping crews throw the pots away so they don't have to pay an employee to take the time to rinse and sterilize them so they can be reused again.
Step 7: Air Supply
If you happen to be growing plants in a large soda bottle (hopefully clear plastic, not green), the plants growing inside it will appreciate it if you unscrew the cap for a while. Breathing into it will replenish the C02 levels inside the terrarium as well. You should unscrew the cap at least once every couple of days.
Air flow will also help reduce disease. If you want a terrarium plant to last a while, try installing a small computer fan into the wall of the terrarium, or even inside the terrarium (be aware that humidity might reduce the life of the fan) It does not need to run on high, but just enough to circulate the air.
Plants in windy conditions will grow more compact, and sturdier than plants grown in a complete absence of wind.