Garden Buddies Soil Amendment

To amend or not to amend. I know you've heard the phrase, soil amendment. But it can be overwhelming, especially as a new gardener. What should you add and when? I hope to answer at least a few of these questions and point you in the right direction.
Sometimes you won't need to amend. If you are lucky enough to have a healthy raised bed garden, you can go several seasons before needing to add anything to the soil. The reason being, a raised bed has less problems with nutrients washing away and is likely to be uncompacted and full of air and moisture.
Crop rotation can lessen your amendment needs. Some veggies/flowers are heavy feeders, some are light feeders and others fix nutrients into the soil, like peas and beans. A good book can tell you which does what, so I won't post all of them here. (I like "The Gardeners A to Z Guide to Growing Organic Food") If you rotate your heavy feeders to grow where you had beans last season you can lessen the nutrients you need to add to make those plants happy.
Most literature about soil amendment frames the concept in NPK language. NPK stands for Nitrogen, Phosphorous and Potassium. This whole way of thinking about soil amendments comes from the Green Revolution and sees soil only as a sponge-like medium, inert and good only for holding the petroleum based fertilizers that deliver massive doses of NPK. Furthermore this framing leaves out micronutrients and minerals and beneficial insects and mycelium. It's like saying humans need only fat, carbs and protein. :-P
But, it's what the industry uses, so here's my advice. If you must buy some packaged soil amendments, aim for well balanced. There are cases, particular soil types/plant types/problems where you want something heavy on a particular nutrient, but for the most part you won't.
Your best bet is to just find some well-rotted compost locally. Sometimes your city will have a composting service, sometimes local garden centers will have local compost, or you can make your own! (Making your own takes time though, so you can start it this year and have it ready by fall or spring of next year, but not in time for early spring amendments this year.) Layer that good moist black compost an inch or two deep over your garden. You can mix it in with a tiller or a shovel, or just leave it, it'll do its job either way. :-D
Its job is to increase nutrients and organic matter in the soil, generally making your veggies happier. Nutrients for them to grow with, and organic matter to help with moisture control, feed beneficials and to keep the soil friable.
You can go overboard with amendments. You can 'burn' your plants using amendments with too high Nitrogen. You can also encourage the 'wrong' type of growth, i.e. plants growing more leaves than fruit. If you stick with compost you'll find it really hard to do either of these things though.
Another great amendment is worm castings. I keep a tub with red worms in a mudroom off my kitchen. When it gets too cold for the compost pile, (compost needs warmth to properly decompose) I switch to the worm bin for food scraps. More about keeping worms later, for now, just know that worm castings make great amendments. You don't need a couple of inches worth either, just a light covering does the trick. You can also make worm casting tea for a liquid fertilization. Google "worm casting tea" for directions and usage.

Some specific amendments I use:
Tomatoes -- heavy feeders-- when transplanting the seedlings to my garden I dig a DEEP hole, I add in a tablespoon or two of worm castings and two crumbled egg shells. Then I bury that transplant deeply. The eggshells provide Calcium to ward off Blossom End Rot.
Peas -- not a heavy feeder, but they tend to do better with nitrogen-fixing soil inoculate. It's a powder you can buy almost anywhere that sells peas.

Don't forget to spread some compost around your perennials too.
I hope this shed some light on the complicated subject of soil amendments. Now is a great time to add them, as the snow melt is done and the ground is thawed. A second feeding can be beneficial for many veggies around flowering time. Again, a good book can tell you which veggies will respond well to that.
Happy gardening!