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Fertilizer basics

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TasunkaWitko View Drop Down
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Joined: 25 January 2010
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    Posted: 14 September 2010 at 14:25
this is outstanding information, dan! thanks for posting!Clap
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daniel77 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote daniel77 Quote  Post ReplyReply Direct Link To This Post Posted: 14 September 2010 at 13:49
As some of you may know, I'm a professional landscaper/horticulturist here in South Louisiana, and I've seen the dirty "F" word occur a bunch of times throughout the gardening threads, so I thought I'd take a minute and shed a bit of light on what is really going on in this area. I also had a 2 acre vegetable garden in high school, which I sold vegetable from, so I have a bit of experience in this area. Of course, I'm going to be brief and general here, as volumes of books could be filled on this subject, and our respective areas of the country/world can vary greatly.

Fertilizers  basically provide nutrients that are broken into two main groups: Macro and Micro nutrients. The Macro nutrients are N, P, + K (Nitrogen, Phosphorous, and Potasium or potash). There is no mystery to how these work or what they do. Think back to 3rd grade and Photosynthesis. Plants use sunlight, air, and water to make food. Think of the fertilizer as merely a component that provides building blocks for food.
There are many different forumlations of fertilizers, and it can be easy to get caught up in the lingo.
All fertilizers, be they grainular, liquid, or whatever, will have three numbers showing the concentrations of N,P, +K and ALWAYS in that order. Miracle grow, for instance, and this may be a SHOCK to many of you, is a very simple and basic 8-8-8. Meaning that it is 8%Nitrogen, 8%Phos., and 8%potash. This is a very good basic recipe for most applications. You are always better off going with lower concentrations than pushing the upper envelope, unless you really know what you are doing.

Nitrogen primarily deals with vegetative growth (think leaves and stems). This is one of the least useful, and potentially harmful ingredients with regard to gardening. You do want your plants to have enough vegetative growth (leaves) to support the functions of the plant, however, if you oversupply your plants with nitrogen, they will primarily produce leaves and not fruit. A lawn fertilizer, for example, would be highest in N, and lower in P + K because you want the lawn to grow primarily leaves to look pretty. If you are growing a legume, like peas, you DO NOT want to use very much N at all, or you will merely produce copious amts of vines and very few peas, because legumes, properly inoculated, capture N from the atmosphere in amounts in excess of what they can use, and actually return it to the soil making your next crop behind legumes somewhat pre-fertilized.

Phosphorous primarily deals with root development. Take that especially into account if your are growing something that is primarily root fruit, like potatoes, carrots, onions, etc. As I recall, P also has a lot to do with the overall health of the plants, and immune systems. You can actually buy a product called triple super phosphate, which is nothing but P, and it will turbo charge your garden. P can build up in soils however, and is not needed in super high amounts for good success.

K or Potash primarily deals with blooming. If you are growing a crop that produces fruit from a flower, as most do, this is very important. If you are growing annuals for flowering purposes in your yard, the same would apply. Potash, like Phos. is not needed in super high amounts, but is needed in adequate amounts for good and especially successive blooming. Many plants that produce large amounts of bloom (could be roses, tomatoes, peppers, whatever) are fairly heavy feeders and will require regular fertilizing.

A few basic rules of thumb for fertilizing:
Fertilizing in general has an acidifying effect on the soil, and soil pH is one of the MOST IMPORTANT numbers that there is with regard to successful gardening. This being the case, even if you start with ideal soil pH, over time, fertilizing will cause it to be lowered. I am located in South Louisiana, and our local soils are known to me. We regularly have to add lime to adjust the pH so that nutrients are available to the plants. This is critical to know. If the pH is off by too much, your plant will not chemically be able to absorb nutrients, so it may be starving even though you've done a very good job of fertilizing. In my area, at least, you can take a soil sample to the local county agent and they will test it for you for $10. You can also tell them what you plan to grow in that particular soil, and they will tell you exactly how much of what to add in order to get it just right.

Time released fertilizers are much more forgiving than regular fertilizers because their effect is spread out over time. They are, however about 5x more expensive. Regular fertilizers must be watered in and used completely after opening. The sad, but true, truth is that within a few days of applying a non-time released fert. the unused N will dissolve into the atmosphere. For this reason, you would always want to water it in as quickly as possible, and be sure to seal up any open containers, lest your Macro Nutrients escape.

It is better to underdo it, than overdo it. Plants that uptake too much fertilizer, especially N, will burn and possibly die. This can even happen with low doses after periods of drought. During periods of drought, it is a good idea to water the plants before and after fertilizing, because the plant's thirst for water could cause it to uptake too much fertilizer as it absorbs as much water as possible.

Micronutrients are a whole nother ball'o wax. They can be very important, but a lot more knowledge is required to understand the intricacies of what they do. One tip I can give is to use a general purpose micronutrient provider like Ironite. Some plants benefit more from certain Micronutrients than others. For instance, tomatoes which begin to rot at the tip (blossom end rot) will be completely cured with a small amount of Calcium added to the soil.

Here is a good link that I found, and feel free to fire off any questions, as I could go on forever on this subject.
http://houseplants.about.com/od/howtousefertilizer/a/indoorfertilize.htm

Another tip, while I'm thinking about it, is to be mindful of your plant's water vs. air needs. Most people don't realize that plants breathe, even through their roots. This is why you'll see someone haul in a bunch of dirt under an old oak tree to cover up all those unsightly roots above the ground, and a few years later the tree dies. They smothered it to death and didn't know it. Cypress tree knees are grown specifically so that the roots can breath and have adequate air, as they are generally under water or in saturated soil. I say all of this so that you can simply know that over watering your plants doesn't kill them, but filling up the soil (with water) so that there is no air available does. This is why you can successfully grow many plants upside down. The roots can get above the water and have all the air and water that they need. This is also why heavy/clay soils are generally more difficult to grow things in. It all comes down to soil particle size and availability of what the plant needs.
Organic materials primary use is water absorption. That's right, adding all of that compost to your soil does provide nutrients, but the main reason to do it is to keep the soil from drying out too much. Take notes, if you have high organic content in your soil, most easily determined by the color, be careful not to over water, as it will stay wetter than you think. Darker soils have more carbon, or organic material. Paler soils lack organic material, or carbon.

Do you think Al Gore realizes that all that terrible carbon that he's always worried about is actually necessary for life as we know it to exist?

As I said, fire away.


If what you're serving comes on a cracker, you'd better have a lot of it.
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