Water: The Life Force of Misunderstandings and Other Soggy Sorrows

It is funny to think that just two months ago I was cursing the persistent rain clouds in the June sky blocking some much-needed Vitamin D, and now I sit under a clear blue yonder praying for a little moisture to relieve our aquifers and me from my duties as sole caretaker of all my potted and planted dependents.

Dry is the Pacific Northwest summer, and that should not come as a surprise. Nonetheless, I always take spring rains for granted in the management of landscapes, which in turn encourages a sort of amnesia to set in over my faculties to decipher an appropriate watering regimen for my garden. As soon as the hose is abruptly passed to me, I feel like a first-time babysitter put in charge of a bunch of hungry kids with different food allergies at snack time.

Much about our plants’ water needs tends to be up for interpretation and thus one of the more frustrating aspects of gardening. When buying a plant, the tag at the nursery will say something cryptic, like “average” or “low.” These precise amounts and frequency of delivery are not specified but depend on other factors affecting the site where the plant will reside. Will it be in the ground or a container? How well does the soil drain? Is there organic matter? WILL YOU MULCH?!

“Watering landscape plants is one of the most misunderstood tasks facing gardeners.” This is the opening sentence to a section about watering in “Sustainable Gardening: The Oregon and Washington Master Gardener Handbook.” I’m glad the experts acknowledge our common struggle to find clarity on the matter.

While plants have their own special way of telling you if you’re doing it wrong, typically by dying, there are signs that can indicate an imbalance occurring. Unfortunately, these signs, like yellowing of leaves or stunted growth, can also mean nutrient deficiencies or disease. It is only when we work to water properly that we can make our best guess at determining other problems that may arise.

The Master Gardener Handbook states that for plants in a landscape, a “good rule of thumb” is to soak the entire root zone of a plant and then let the soil “dry partially before watering again.” This means the first few inches of soil around the plant should be completely dried out. How much you let it dry out “depends on the species and its size.”

Soil around big established trees, shrubs, and perennials with “low” water needs can dry out quite a bit before needing to get watered again. Soil around newly planted or shallow-rooted trees or shrubs, like rhododendrons and blueberries, shouldn’t be allowed to dry out as much. Perennials with “average” water needs fall into this category as well. Watering established native woody plants, like Pacific dogwood and madrone, should be avoided because moisture in the summer can cause root rot.

Deep (penetrating to 6-plus inches down) and infrequent waterings (once or twice a week in hot weather) are best for root development. Watering too little or too much results in weak, shallow roots that won’t be able to withstand prolonged drought. Soil conditions will play a big role in how successful water is at penetrating the depths of the root zone. If the water pools up on the surface and runs off, the soil should be amended to improve water-holding capacity and prevent nutrients from leaching out.

Plants in containers and the vegetable garden require a slightly different approach. Many plants occupying these spaces tend to be annuals and have shallow root systems, which means watering needs to be done more frequently, though there are outliers like tomatoes, cosmos, and sunflowers, which can handle a few days between waterings.

Waiting for the first few inches of soil to dry out in containers and raised beds is still a good measure of when to water, but the frequency can range from daily to twice a day depending on the weather. The best time to water is at night since there is less evaporation, but any time of day is just fine too.

How you deliver water is a matter of personal preference and resources. Drip systems are ideal because the emitters are closer to the soil and can be put on a timer. Hand-watering from a hose or can is great for containers but not so much for trying to cover the entire landscape since you’re not likely to stand in the same spot long enough to allow the water to soak in thoroughly. A moveable sprinkler is effective and far more efficient.

The amount of time the water should stay on is anybody’s guess. I like to start at 15 minutes and work from there. But if you’re tired of guessing, sub-irrigation systems in containers and raised beds are gaining traction as a water and time-saving solution. Through this method, a reservoir sits under the soil and water is wicked up as the plant needs it. A floating indicator lets you know when to refill. These systems can also provide a good visual to show exactly how much water our plants are using on a daily basis.

I wonder if perhaps they are a key to resolving our misunderstandings? Or at the very least, will allow us to enjoy these months of endless blue sky without having to wonder, “Am I doing this right?”