The kitchen garden soil needs the right amount of water and a good fertilizer to maintain its good qualities.
To produce a healthy, productive garden you'll need loamy soil. It should crumble easily in your hands, not too much clay aspect, not too much sandy quality. Clay-like soil retains too much moisture and doesn't allow proper drainage. Sandy soil doesn't provide adequate support and drains too well, as well as lacking needed nutrients.
To produce that kind of soil, two obvious things are needed: good fertilizer and the right amount of water.
But before you add anything, know what you're starting with. A simple and inexpensive soil testing kit will tell you what kind of soil you have. It will test for levels of nutrients and for pH. Some vegetables like a more acidic soil, others prefer an alkaline earth. Most will do best in an intermediate range of 6.0-6.5.
Adding sulfur or lime can adjust the pH. Adding fertilizer will supply those nutrients. pH should be adjusted several months before planting. In some climates, that means doing so after the prior years harvest, before the snows start.
If you've created a compost pile, add the material to the topsoil about three weeks before planting. That will give it time to naturally leach the needed nutrients into the soil before you plant. You can speed up the process somewhat by tilling it into the top few inches. Otherwise, you can add organic or artificial fertilizer (such as NPK 8-8-8) to enrich your soil. Add that right before planting. About 20 pounds per thousand square feet is enough in most cases.
Unlike most herbs and some other plants, vegetable plants love lots of water. Like nearly any plant, most shouldn't sit continuously in a bed of water. That will lead to root rot. But a continuously moist soil will provide the water needed to power the biochemical reactions that plants carry out to grow and support themselves.
Water is a vital chemical used to transport nutrients throughout the plant, participate in photosynthesis, and give rigidity and firmness to cell structures. About an inch of water per week is the right amount for most gardens. That works out to about 65 gallons per 100 square feet. The amount will vary slightly depending on the type of soil you have. If natural rain activity doesn't supply that amount from April through September, you'll need to supplement it.
Fortunately, it's easy to supply.
Unlike flowering plants, watering vegetable plants from above doesn't wilt them if applied in moderate temperatures. Still, some of the same considerations apply. Try to water early in the day, in order to allow leaves and the top layer of soil to dry out before nighttime temperatures arrive. That keeps problems such as fungus down. Another way to accomplish the same goal is to build a simple and inexpensive drip irrigation system. Rubber tubing that leaches water should be placed near the plant in order to supply water to the roots.
Then, only occasional water is needed to keep leaves clean and their pores open. Don't water when it's very hot, though. That defeats the purpose, since it causes the pores in the leaves to open, and they evaporate more moisture than you supplied. It can also cause burns when water droplets act like small magnifying glasses