OK, by now you’re probably getting pretty tired of hearing about all the things you’re doing wrong in the garden. But to be honest, with the long list of constraints put on home gardeners, it’s a wonder we can get anything right.
We all know that the native dogwood (Cornus florida) for example, does best on a soil that is deep, rich, moist, and slightly acidic with a reasonable organic matter content and minimal competition from roots of other plants. But exactly where does that exist? Maybe on the mythical planet Gardentopia. Last I checked, and despite years of effort, I still have poorly drained, heavy, and nearly neutral pH soil that is overpopulated by roots from the neighbor’s big ash tree.
When it comes to managing, and particularly to watering lawns, getting it right can seem downright impossible.
Let’s start this discussion with the assumption that you have or want a traditional lawn of primary turfgrass. Sure, there are non-turf “lawn” options that can reduce mowing, save on water and make you feel all sustainable, responsible and greeny, but they’re not all that great for a neighborhood pick-up game of soccer, ultimate Frisbee, or fetch with the family dog.
Grass is king for a reason. We’ll just start there.
Now, you are all astute and attentive readers so you know from past columns that watering deeper and less often is better than watering more often and for shorter time periods. The general concept is that deeper watering encourages deeper rooting. Short, frequent waterings end up concentrating grassroots in the upper inch of soil, and thereby requiring more frequent irrigation and resulting in less resilient lawns.
But the water-deeper-and-less-frequently thing is all fine and good if your lawn is built to USGA golf green standards. The best golf course greens on this planet are built on a highly engineered layer cake of gravel, sand and soil to allow the greens to absorb vast quantities of precipitation and remain playable. The construction also allows course managers to make fine-scale adjustments to the moisture (and for golfers, firmness) status of the surface. It’s a perfect combination of rapid water absorption and drainage, water retention and root zone aeration.
Helps to have access to a certified golf course superintendent also …
The average home lawn is anything but a USGA golf green.
Most home soils have been essentially irreversibly compacted during construction. To make matters worse, most residential construction is accompanied by the removal of what little topsoil may have been there to start. What remains is anything but well-drained. Indeed, some post-construction soils have been determined to have a bulk density greater than that of a fired clay brick!
But the most useful statistic is that most residential soils absorb no more than about one-quarter-inch of water per hour. Think about that. If you run your sprinkler for 30 minutes, on average, the water that lands on the lawn will only make it the thickness of a dime into the soil horizon. Four whole hours to get the water just one inch deep. When was the last time you watered the lawn for four hours … or eight?
The second thing to consider about watering the lawn is how the water is delivered.
The above discussion about water absorption rate only considers water that actually lands on the soil surface. The problem with most irrigation systems is that in many cases, the lion’s share of sprinkled water never gets into the soil.
Consider a 90 degree August day with 60% relative humidity, sometime around noon. Fire up the sprinkler system then and on average you can lose almost a third of your water to evaporation before it even hits the ground. When you add in evaporation from the surface (before it gets absorbed into the soil) and surface runoff, you can lose up to 80% of your water.
Not very efficient.
Overall, this all seems like a no-win situation. So what’s a homeowner to do? Here are three tips:
Invest in long-term cultivation of your lawn
Not much you can do here. Unless you’re going to dig up the whole lawn and replace it with 18-inches of engineered mix with subsurface drainage (which, in case you are wondering, I am not recommending!) you’re pretty much stuck with what you have. The good news is that long-term cultivation of good, deep-rooted lawn species can itself add organic matter, improve soil quality and help some overtime.
Re-think the time of day, and how, you water
This one has both a quick and easy and a more complex answer. First, don’t irrigate in the middle of the day when the evaporative potential is highest. The best time to irrigate the lawn is first thing in the morning so you can rehydrate the lawn and soil before the heat of the day. Avoid evening lawn irrigation since water droplets on the grass leaves during the night can result in significantly increased disease pressure.
The second, and more complicated part of the irrigation timing thing is what’s called pulse irrigation. If you have poorly drained soil, running the irrigation system for two straight hours results in most of the water running off into the street and down the storm sewers — wasting a whole bunch of treated municipal water.
If you are trying to get the water deeper into the soil while also minimizing surface runoff, consider short, frequent bursts of irrigation. Run the sprinkler just until runoff starts. Turn it off for a bit to give the water time to filter into the soil. Then hit it again, and again. The only way to know how to time this is to actually spend a morning out there watching. Balancing water delivery pace with soil absorption rate will be different for everyone and will depend on water pressure, sprinkler head design, soil type, etc.
Consider your sprinkler system design
This is a tough one because you only have access to what manufacturers make available. But there is some flexibility. Most of us are human and subject to what seems obvious. Minimize the cost of an expensive irrigation system by putting in fewer heads and ramping up the pressure to increase coverage. But this actually increases the evaporation loss problem. Higher pressure usually means smaller droplet size which in turn means greater evaporation potential. Operating at a lower pressure is the way to go. A good irrigation system designer can work with you to achieve a good balance for your conditions.
If you don’t have an in-ground system but use a portable, hose-end sprinkler, you’re in luck. If you install one of those in-line shut-off valves between the hose and the sprinkler, you can dial back the water flow to the sprinkler which will, in turn, reduce pressure and increase droplet size. Sure, you have to move the sprinkler more often compared with running it full bore. But it is something you can actually control. And besides, I hear that’s what the beautiful people do on Gardentopia!
Paul Cappiello is the executive director at Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.