For in ground plants fertilizing is a crap shoot unless you have a soil test to tell you what is and isn't in the soil at adequacy levels.

Many would deal with the uncertainty of soil fertility by adding various organic matter and calling it a day. Others will handle it by scratching in some 10-10-10 and calling it a day, but it is all a crap shoot unless you know what the soil does and doesn't need.

In my state, as an example, we have excessive levels of phosphorus. As a result I would never add it intentionally because excessive P can and will cause problems with availability of other nutrients. Our soils also tend to have adequate to high levels of potassium depending on the plant. As a result I never add K except for plants I know to use higher than average amounts such as my grapes.

In general the only nutrient that is safe to add to most any soil is nitrogen and that is because plants use a lot of it and it tends to be the first nutrient to leech below root level in soils. Beyond that, please get a soil test. No need to get one every year, just get one to get a baseline idea of what your soil does and does not have and then you can make intelligent, informed decisions.

In addition to all the good points made in justaguy's post, many of your crops have different fertilizer needs in time of application, amounts needed, and types of nutrients needed. So there isn't a "one for all" solution ;).

EX: like beans and peas, beets don't tolerate lots of N and while tomatoes, carrots and beets will benefit from higher levels of phosphorus, melons and cukes don't.

That is one reason so many elect to go with the "add lots of organic material/compost" approach...to at least cover the minimum needs for all and it has the added benefit of somewhat neutralizing your soil pH at the same time so the nutrients are more useable.

But if your soil pH is way out of kilter then it makes no difference how much or in what form you add nutrients - the plants can't use them. Thus the need for a soil test. Once you have those results then you need to research the nutrient needs of the individual crops you are growing and treat each accordingly.

And please, don't buy into the MG advertising that just hosing down the garden weekly with lots of MG will result in magnificent growth and production for all. It just doesn't work that way in real life. ;)

Dave