Irrigation seems intuitive when you watch someone else do it. The soil appears dry, the leaves seem wilted, and you want to water. This works terribly for new farmers because the decision to water involves far more than the presence of moisture. It involves when to water, how much to apply, how often to return, and how well the soil retains that moisture between waterings. Under-watering can be a problem, but so can overwatering such that the rootzone never has a chance to breathe. If you’re new to farming and want to develop a sense of when to water, start with the following exercise.
Separate your field into two small subplots that grow the same crop. Visit both every 24 hours. With your fingers, feel the moisture of the top inch of soil in each. Then dig down a few inches and compare. Check the plants in the morning and later in the day. Some plants will wilt in the afternoon heat and perk up in the evening, a sign of a very different stress than leaves that remain wilted all day. This comparison will teach you more about when to water than will watering every time you see a wilted leaf.
A very common error among new farmers is to rely solely on topsoil moisture to dictate watering. Depending on weather conditions, the top two inches may dry while the soil below remains plenty moist for root growth. The result is a tendency to water too frequently and too lightly, resulting in weak roots that demand even more frequent watering. The simple solution, which can easily be overlooked, is to always dig down before making a watering decision. If the subsoil feels cool and retains some moisture, wait a day and check again. If it’s dry down a few inches, water more deeply rather than just splashing on some water.
Here’s a framework that might help you commit to this exercise for a few weeks until it becomes a habit. Give yourself 15 minutes during every watering cycle. For the first 5 minutes, check the soil moisture of two or three different areas of your field and compare the moisture of soil in full sun with the moisture of soil in full shade.
For the second 5 minutes, observe the turgor pressure of the leaves (how firm they are or aren’t), the color of the leaves, and whether they’re beginning to curl under at the edges. For the final 5 minutes, write down one observation about what you thought you were seeing and one observation about what you actually saw. That last one is important. It helps you see where your expectations led you astray. Your ability to judge the right time to water will improve as you test your expectations against reality over and over again.
Finally, when in doubt, don’t assume every sign of stress is a sign to water more. Make sure you’re not overlooking other issues that can cause similar symptoms, such as inadequate aeration due to soil compaction, poor internal drainage, root-bound soil, or a recent dramatic shift in temperature. If you’re still unsure what to do, make just one change and observe how well your plants respond over the next few days. An extra day or two between waterings, or an extra inch of depth, or digging down just a bit deeper before making a decision can tell you a lot. As you go, you’ll respond less to every sign of stress and pre-emptively water less, making your system overall more efficient and less likely to reduce your yields.