Can I reuse vegetable oil as a fertilizer around my green plants? What about chicken broth, after I have removed the chicken after boiling?
I would not use the vegetable oil as a fertilizer (though many people use it as a pest control).
The chicken broth would have benefits, but adding it to the soil will attract animals, like raccoons, that you would not want in your yard.
What does each number do, and which number would help hold the fruit of the tree?
I like to remember what the three numbers on the fertilizer bags are in this way. They are typically referred to as the N-P-K. The first number is UP the second number is DOWN and the third number is ALL AROUND. The first number is good for the upper part of the plant or bush. The second is good for the root system of the plant or bush and the third number is good for the all around feeding of the plant or bush. A high first number or basically Nitrogen content can create more foliage and less blooming or fruit production in some cases. If you are looking for something to build the root system up then you want a fertilizer with a high second number. Usually a well balance N-P-K rating is what you want. Just remember; Up - Down - All Around. :o)
Stan
Will a 12-12-12 fertilizer fix my low nitrogen problem?
Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/nitrogen-nodules-and-nitrogen-fixing-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/nitrogen-plant-fertilizer.htm
What are the benefits of Epsom salts to plants?
It helps add calcium to the soil. Plants need calcium to grow well, particularly fruiting plants like tomatoes and squash.
Should I even garden if fertilizer was used in the place I would like to garden?
It will not harm the plants or you. If you want to garden going forward with organic methods, do this. The fertilizer that is in the soil is not dangerous to edible plants, like a pesticide would be, but is more harmful to the environment. Since the damage is done already, you just have to make sure that further damage to the local environment does not happen going forward.
When is the best time to use liquid feed?
You can use liquid feed the same as granular. If you are using it as a foliar feed, you should use it in the early evening to allow the plants to absorb more of the nutrients before it evaporates.
Can I use coffee grounds in the garden?
Yes, you can. This article has more information:
https://www.gardeningknowhow.com/composting/ingredients/coffee-grounds-gardening.htm