How much is too much? How little is too little? These basic watering questions have foiled many a gardener. While water is essential for any garden plant, factors such as soil, humidity, and sunlight can make a big difference. Clay soils hold water best, but take a long time to absorb. Sandy soil absorbs water very quickly, but can't hold much. You want your soil to have enough organic amendments to retain moisture and allow spaces for air to reach the roots.
What you have in your garden will also determine how much water you need. Root depths vary greatly. Tomato roots can reach 2 feet deep after a good season, while lettuce roots may be only 1 foot deep. Other plants grow even shorter roots. If possible, try to take note of how deep the roots are of your different plants.
You also have to remember the rate of evaporation. Hot, dry, windy days suck up moisture out the soil much faster than still, humid days.
Either with a hose or a watering can, hand-watering is the simplest and possibly the most common method of watering in gardens. It requires no special preparations. The only real drawback is that people get impatient and often water less than enough for their plants. If you hand-water, be sure to check the rate of absorption. If your soil is mainly clay, don't be fooled by runoff. You may think that the ground is saturated, but it simply can't be absorbed fast enough. Water your plant until water runs off, then come back after an hour or so and water again.
Furrow irrigation is used with plants that are planted in rows. Ditches or furrows are dug alongside the row of plants. These furrows are flooded, allowing a deep absorption of water. This method usually allows the foliage to stay dry, which helps keep diseases to a minimum.
Either attached to your hose or built-in, sprinklers are great for densely planted vegetables. If you need water placed evenly over a large area, this is the technique for you. Keep in mind, though, that sprinklers put a lot of water on foliage, which can lead to disease. Also, weather factors such as wind and sun can decrease your watering efficiency. Don't use sprinklers on sparsely planted vegetables, as this will waste water.
This technique allows a slow, but steady amount of moisture to seep into the soil around your vegetables. Using a soaker hose or a trickle irrigation system, this technique can be left on for hours. Use this method around thirsty plants and on gardens planted on slopes.
Even though the soil surface is wet, or dry, you can't always tell what's going on at the root level. To see if you've watered enough, take a long screwdriver and stick it into your garden soil. If it goes in easily, you've watered enough. You can also purchase a moisture meter at your local garden center. Other than checking for moisture, keep these tips in mind:
Water after planting
Water before leaves wilt
Water in the morning
Water established fruit trees and berry shrubs deeply but infrequently