I make compost in my backyard. I also buy fertilizers for vegetable and fruit plants from the big box stores. My question is really when to use compost vs. fertilizer? Can I eliminate the use of fertilizers if I have enough compost or do I have to continue to use the combination. If the latter, when do I use each of these? Interested in practical suggestions based on what other's are doing.
No, but it could sensibly reduce or remove needs of fertilizers.
It is not very probable that the compost has the required exact proportion of fertilizer. It is also not so probable that one single fertilizer has the required proportions, but we have many different fertilizers, to choose..
It is possible not to use fertilizers, using compost, straw, hay (meadow, wetland) and different type of manures (cows, horses, chickens), and ev. also with ashes [all of these have different percent of fertilizers and minerals]. But this is complex to calculate, and the above ingredients have a lot of variance, so one should do soil analyses often, to correct deficiencies. Not a thing to do for home garden (but instead it is ok for a large organic farm, where possibly they could analyse the composition of the ingredients).
No, you can not replace 'fertilizer' with compost. You do have to consider the amount of necessary chemicals available and what chemicals your particular compost adds. Fertilizing includes not only the 3 biggies; Nitrogen, Phosphorus and Potassium but at least a dozen micro nutrients as well. Too much of just one of these chemicals in the soil can cause deficiencies as well as excess for plants.
Compost might have lots of nitrogen available but during the composting Nitrogen is used in high quantities. There might be residual bits of all kinds of necessary chemicals the plants need but to think one can do one or the other is ABSOLUTELY NOT.
One of the best information sources I found and use an awful lot is Shane Smith's Green House Gardening. Excellent charts, excellent break down of chemicals to include 'excessive' and well as deficiency symptoms of these chemicals. Since we humans have to be in charge of replacing chemicals, water...we have to be able to SEE symptoms in the plant and do quite a bit of investigation. No one thing will determine the next step.
We humans are learning ways to communicate with plants. There are so many variables we all have to learn to be successful with plants; what plants or a plant needs, what your soil's composition contains, light, water, micro and macro organisms (and they need fed), climate, humidity and individual maintenance rules. Without basic knowledge of plants and there is an awful lot, to learn how to SEE what a plant is telling you...more Nitrogen or more Iron or more Molybdenum, Boron, Calcium, Magnesium etc. Or wait, there is plenty of Nitrogen but too little Iron, or there is too much of one chemical that inhibits another chemical. Top it all off, pH of the soil is so very important to KNOW. One can give their plants plenty of chemicals, in the correct proportions but if the pH is too alkaline or too acid for that particular plant, that plant will not be able to uptake Nitrogen for example. Far more complicated than people are hoping.
Decomposed organic matter or compost is important for soil texture and feeding the micro/macro organisms in the soil. You have to know what is in that compost before augmenting with fertilizers.
The best method is being frugal with fertilizer and learning what your plant is telling you it needs by colors, textures, patterns. Shane Smith's book and there are others (another great book that has this information is Jorge Cervante's Cannabis Encyclopedia) to help you to understand what your plant is 'telling' you it needs.
Over fertilization is far worse than too little! Once you've gone 'over the line' that plant will most likely die. Too little the plant can live quite awhile until the human in charge can see what that plant is saying (screaming) it needs.
NO, compost is NOT a replacement for fertilizer.
I have never fertilised any of my vegetables or fruit trees apart from using compost and compost tea. I would challenge that you need to add fertiliser to your vegetable garden especially if you use crop rotation and plant diverse range of vegetables together as companions.
I use worm casting from my worm farm to brew my compost tea. Making compost tea: http://www.homecompostingmadeeasy.com/composttea.html
Your home produced compost is a very valuable addition to soil, but it's not the same thing as a fertilizer. Fertilizers are prepared products with specific nutrients which are intended to feed plants directly - compost, and other humus rich materials, improve the soil in order to allow plants to seek out their own nutrients easily, which are more likely to be present because of the composted material. Adding humus rich materials to soil on a regular basis raises soil bio diversity, and that's a good thing - the more organisms per square foot of soil there are, the richer and more fertile the soil becomes, making a much healthier environment for growing plants. This is the approach used in organic growing, where the soil is of primary importance, rather than feeding plants directly with fertilizers, and is an approach which is worthwhile following as far as is possible.
I haven't used a fertilizer regularly on ornamental plants in gardens for ten years or more, with one exception - roses, which do get a specialist rose food twice a year, and in some years (if the winter's been very wet) a single topdressing of Growmore (NPK 7-7-7) in spring annually to the whole garden, topped off with organic mulch (usually composted animal manure), as growth begins. Applications of composted materials to the soil are made at least annually as an absolute minimum, to keep the soil in as good a condition as possible, preferably applied as a mulch, coupled with no digging as far as possible to preserve soil structure.
The same is not true of potted plants - they will need fertilizer applications.
As well, if you are growing your own vegetables, amendments may be necessary - to raise or lower ph a little, or to increase nitrogen or phosphate levels, depending on what you're growing.