Most growers, particularly new ones, find irrigation to be one of the most troubling aspects of farming. Rightly so, since water, along with nutrients and sunlight, may be the most essential ingredient of life—if you don’t believe me, just ask any Martian. If your sensory hierarchy leans toward the visual, you may think, like my mother-in-law and my mother, that a wet surface means you’ve irrigated, and when your just transplanted nursery stock starts wilting you may be bewildered. After all, you sprinkled the plants and the ground looks wet. But stick your finger in the ground and just below the surface you’ll likely find dry earth—it takes a lot of water, and gravity’s aid against the soil’s resistance, to provide plants the underground moisture necessary to quench the thirst of roots, stems, leaves, and blooms.
A lot of younger growers, brought up on the wonders of technology, immediately want “the answer”—an app to tell them when to water, how much to water, how often to water. It’s a normal reaction, but if the app for irrigation does ever show up, that will make you, as a grower, that much less needed, because it’s your expertise that makes your enterprise fly—if a flower farm were like an IKEA living room, then anyone could put one together, and if anyone could do that, wouldn’t it make you irrelevant? The history of farming is riddled with technological solutions to problems that shrank the number of farmers and farms as farming became easier and consequently less profitable, which required bigger farms and new technologies, which required lots of capital and debt load, and resulted in farmers becoming dependent on huge support systems for their tools—electricians, mechanics, pump specialists, and the host of other workers who made, sold and serviced their toys (whoops, I mean tools).
In any case, you already have apps—your fingers, your hand, your brain, and if needed, a trowel or a shovel. Plants don’t need surface water so much as water at the root level, so you need to use those apps to see what the soil looks like where the roots like to be—if it’s a shallow rooted species, check the top two or three inches of soil, and if it’s a deep rooted species, go down deeper. If you subsurface irrigate, as we do, it’s easy to tell when there’s water deep, because the below-ground drip tape wicks water upward at a slower rate than gravity pulls it downward, so when the surface appears wet, we know the soil is saturated at drip tape depth. But if you surface irrigate, there’s no way to know what the soil looks like underneath without checking. You can guess, you can trust your guess, but even those of us who’ve grown for decades can guess wrong—and we often do. Depending on soil composition, the top inch of soil may be muddy and anything deeper completely dry, or the top can seem somewhat dry while there’s plenty of water deep (sandy surfaces can appear this way). So, you can imagine your plants need three hours of water, set your timer and walk away, or you can check the soil by digging into the soil after a couple hours to see how water’s progressing and go from there. You may get away with the first method for a while, but eventually your luck will run out—and I will note on your resume that you shouldn’t be in charge of a nuclear reactor, where small mistakes have bigger repercussions than you mis-irrigating.
In general, deep irrigating established plants is more effective than frequent, shallow irrigations. In warmer climates, evaporation works on the upper levels while deep water holds like a bank account, releasing as needed. On direct seeded crops, deep irrigation is initially unnecessary, since only the top inch (or less) is necessary to instigate germination. Once seeded crops germinate, check deeper into the soil, and if there’s adequate moisture hold off on further irrigations—the roots will seek out deeper water, driving them to a depth where they can use heavier irrigations in the future. Young plants aren’t losing water through leaves (transpiration) as older plants do, and they aren’t using much water for growth, just as an infant requires far less sustenance than a professional athlete. Let direct seeded crops go without water once they’ve emerged—we skip at least an irrigation cycle or two, depending on the heat, because applying more water than necessary not only gives weeds a chance to germinate but actually can permanently stunt some species. Bells of Ireland and Broom Corn are two species that, if overwatered early in their life cycle, may never recover from soil saturation, and there are many more that will be set back by getting too much water too early.
When transplanting, heavy irrigation may be essential—the more established the plant, the more contacts with the soil you’ve severed, so each root has lost its connection to its water source. It may take several days in saturated soil for an older plant to situate comfortably in new environs, so check frequently, adjust irrigations according to the weather and the soil type, and if leaves look wilted, you may even want to trim them back heavily so the plant can use available water to restore its root base rather than wasting it on foliage.
Dormant crops don’t want more water than the minimum necessary to keep roots or bulbs from desiccating. This may mean no summer irrigation at all—we don’t irrigate alliums or eremerus, and even tulips and daffodils can last decades with only minimal winter moisture—nature’s work is often very efficient.
Fleshy rooted species generally retain water well. Those thick roots hold moisture, provide a bank to get plants through droughts, so don’t overwater—especially before winter’s arrival, as saturated rooks, when frozen, may “explode” when water cells turn to ice, whereas plants left drier have room for those frozen cells to expand without destroying the integrity of the root. Know your species and irrigate accordingly.
Likely, if you’re a small grower, you’ll have small plantings that don’t correspond to row length, so group species according to their needs—drought tolerant with drought tolerate, waterhogs with waterhogs. If you irrigate aboveground, you can group plants with different needs on the same drip line if you use valves between species, so long as the big water users come first on the line and low need species are last—just turn off the water every cycle or two between the species with different needs.
You’ll probably need to make concessions regarding the “perfect irrigation” unless you have large acreages, because only rarely do two species have exactly the same water needs. If you have multiple species in a row or on a zone, you’ll have to aim for middle ground, watering the hogs less than they want and the frugal species more than ideally. Unless you’re able to perfectly group plants with similar needs on a zone, always use connections with valves and USE THEM, irrigating transplants more than direct seeded crops by turning off the lines to the latter.
It takes years of practice to get a feel for irrigation, but you’ll find yourself making fewer and fewer mistakes If you assimilate the feedback given by your plants. Change your methods according to what they tell you and eventually you’ll get your black belt in irrigation.