Vegetable gardeners are preoccupied with precipitation, and for good reason. Not only do plants need moist soil to grow and bear fruit, but garden produce also contains a lot of water.
Take a 6-inch cucumber, for example. If you put it through a wringer, you'd probably end up with half a cup of pulp, seeds and skin, and at least that much liquid. Same thing for tomatoes, melons and corn (off the cob). Mind you, I'm merely making an educated guess here. Knowing my luck, a reader who still has an old wringer washing machine on the back porch will call to tell me my proportions are off.
Perhaps the better proof is in what happens to fruit on the vine when it rains heavily after a dry spell. I have likened this in the past to putting a balloon on the end of a garden hose. When the ground is suddenly saturated, the skins of tomatoes and melons split easily and cucumbers and zucchini can grow big as your arm overnight. That's because thirsty plants are drawing every available drop of water into the fruit. If the soil remains even mildly damp, even in times of little or no precipitation, a big rain won't produce this effect. Plants drink only as much as they need. If they could talk, they would tell us this. I'm sure of it.
In most years, we don't get enough rain in northeast Kansas to keep garden soil damp, and this is a challenge for everyone except urban gardeners who don't mind increasing their tithe to the municipal water department. The trick for country dwellers and those who are less lavish with their city water is to conserve and make every drop of water do extra duty.
Many folks who have large vegetable gardens never turn a tap and still have good harvests, even in dry summers. Some catch rainwater by running their downspouts into 55-gallon drums, or they pump from a pond. But plenty do no supplemental irrigation. They make good with what Mother Nature gives them in a two very important ways.
They mulch. This keeps the moisture in the soil from evaporating as quickly as it will when the soil is exposed to air. As soon as vegetable plants are five or six inches high, water-conscious gardeners put down the first layer of rotten straw, leaves or grass clippings. As the plants grow in height, put down more mulch.
If you talk to gardeners, they have different approaches to mulching. There's no rule for mulch ingredients, and some gardeners mulch by layering different materials in various orders. For example, people who bag their grass clippings and leaves might lay those on top of rotten straw as a form of insulation.
Fresh grass clippings produce heat and they warm the soil and sometimes create an environment for mold to grow. For that reason, I personally don't put grass clippings down first, when I use them at all. However, fresh grass clippings placed on top of rotten straw will dry in the sun to form a nice thatch over the mulch below, and can even enhance the effect of the mulch.
What you're shooting for is enough insulation, several inches thick, to retard the evaporation of moisture. If you achieve this, you'll be well on your way to doing the second thing that successful low-water gardeners do.
They weed. One of the side benefits of mulch is that it keeps light off of the soil, which keeps weed seed from germinating. If you have a good layer of mulch around your vegetable plants, you'll only have to pull the random volunteers and then weed the open spaces in your garden, which you should be able to do with a tiller.
Keeping the weeds under control is not an aesthetic issue, it's a water issue. Weeds are plants, too, and they compete for water. If you have weeds, your veggies are losing moisture. This also is why any straw you place on your garden should have begun to decompose, so that the seeds it contains have germinated. It's a colossal drag to have to pull volunteer wheat out of your mulch.