Pulling the plug on turf problems
Most turf managers are sold on the value of aeration. After all, what's there to argue about? You know that a loose, aerated rootzone that drains well is a good thing. But aeration is an effective tool for objectives other than simply keeping soil loose. Soil replacement, overseeding and breaking up compacted layers are some other reasons why turf managers aerate.
The part that gets a little more complicated is how you achieve your goal. What are the advantages of solid-tine and hollow-tine units? How many passes should you make when you aerate? How often and when should you aerate? Should you use a rolling drum-type aerator or a powered cam-type unit? For most of these questions, the answer is, “It depends.” As with most cultural practices, the approach you take depends on your goals and the conditions of the turf.
Finding the right time
The time to aerate is dictated by a number of factors. The general rule is that you should aerate turf when it is actively growing. This allows turf to recover quickly from the stress that occurs with aeration, and to exploit the newly loosened root zone. With this in mind, then, you can deduce that spring and late summer to fall are appropriate times for cool-season turf, and summer is best for warm-season turf.
Dr. Bernard Leinauer, a turf specialist at New Mexico State University, points out that for warm-season turf, a consideration is whether the turf will undergo summer dormancy. By definition, warm-season turfgrasses thrive in warmth, but even they will go dormant in the summer heat without water. So Leinauer suggests planning on aerating warm-season turf earlier in the summer if it is unirrigated. This mainly applies to the arid West; the Southeast and Gulf Coast regions tend to receive enough summer rainfall to prevent summer dormancy.
For a number of reasons, experts tend to favor late summer and fall for cool-season turf, though spring aeration is far better than no aeration. But various practical considerations come into play, too.
Dr. Roch Gaussoin, turf specialist at University of Nebraska, feels that spring and fall aeration both can benefit turf, though in slightly different ways. According to Gaussoin, “One advantage of fall is that you're doing it after most of the [season's] damage has occurred. The turf can then take advantage of the winter freeze/thaw because water gets into the soil better. The freeze-thaw process gives you even better soil infiltration by spring. On the other hand, spring aeration may be more effective because soil is already somewhat loose after winter.”
Dr. John Stier is a turf specialist at the University of Wisconsin. In Stier's region, and most others, rainfall is another factor that can affect timing. Stier agrees that, “From an agronomic perspective, fall is the best time.” That's why Stier suggests late August or September. However, on athletic fields, this may conflict with football. Stier suggests, “If football is being played, use smaller tines — ¼ to ⅜ inch — for less disruption. Or you can wait until later in the fall.”
Stier cautions that waiting until colder weather sets in can increase the risk of some winter injury due to dessication of roots within the coring holes. Waiting until spring is another option. Regardless, Stier observes that, “A lot of it has to be timed by the weather. The soil should be warm and not too wet.” So whether you choose spring or fall, weather may alter your intended timing.
Dr. Peter Landschoot, turf soils specialist at Penn State University, acknowledges that not everyone has the option of aerating at the time that's most ideal for the turf. “Not everyone has that luxury. You do it when you can. But this flexibility has limits. Aerating in the extreme drought and heat of summer can do more harm than good.” Landschoot also cautions against aerating too late. “You want the turf filling in those coring holes that same season. That way, the following spring, moss and weeds won't get a foothold.”
Landschoot relates that he once worked on a course where, “We did it the second week in September. That's still prime golfing season.” But it served a purpose: “You don't want to go into winter with thinned out turf. You can aerate into October and maybe still get fill-in, especially if you fertilize.” Landschoot feels that waiting until spring would still benefit turf, and would be better than not aerating at all. “The main problem I see is people not doing it enough…that's the key.”
Even labor considerations can affect timing. Aeration takes a fair amount of labor, and Gaussoin is familiar with operations that time their aerations to take advantage of summer help. “You may be able to time your aeration in summer before people go back to school,” he says
How much is too much?
Aeration, especially coring, injures turf. Generally speaking, the benefits far outweigh the harm, but can you have too much of a good thing?
Several aspects determine proper aeration intensity: the number of times you aerate each year, the number of passes you make and the size and spacing of the tines. No formula can tell you exactly what is appropriate.
Landschoot explains that, “It depends on the severity of the problem. Why are you aerating? To get rid of thatch? Half- or three-quarter-inch tines are not enough to remove significant thatch if you only make one pass. You should go over it several times in that case. If you do this, though, you thin the turf some, so you might want to do it in conjunction with overseeding.”
Turf that has received regular aeration may not require such aggressive treatment. “If you aerate every year, one pass may be sufficient.” By contrast, “One pass every seven or eight years may do nothing at all,” says Landschoot.
Gaussoin concurs. “Routine programs should require only one pass if done every year. Multiple passes are necessary if it hasn't been done in a while. It just depends on conditions.” Take heavy thatch, for example. “Multiple passes multiple times per year may be better than power raking. Raking can take a thatchy lawn to bare ground if it's really bad, but aggressive aeration can be almost as effective” and leave turf in better shape than raking, says Gaussoin.
Stier notes that on athletic fields, thatch usually isn't a serious problem due to the heavy traffic. And on sand fields, compaction often isn't too serious either. But layering more frequently is. Thus, for athletic fields, Stier feels that, “For general maintenance, once a year is enough. But bad soil-layering problems may call for two or three passes, two or three times a year.”
How aggressively you aerate partly depends on aesthetic considerations. After all, coring leaves cores — sometimes, lots of them.
For sports turf, this is, of course, a problem. A typical way of dealing with cores is to drag them, which breaks up the soil in the cores and leaves the small tufts of turf, which can be removed with relative ease. If the goal is rootzone modification, the intact cores may be removed, and topdressing applied and dragged into the coring holes.
In any case, the more aggressive you are, the more you disrupt the turf surface and the more cores you must deal with. One way to reduce the impact is to use smaller-diameter tines. Another strategy is to use solid tines.
According to Gaussoin, “The biggest advantage of solid tines originally was that they were labor savers. You didn't have to deal with cores. That is probably why most superintendents like the solid tines.”
Because solid tines don't leave cores, you might expect them to be popular for lawn care, too. Not so, says Gaussoin. “Lawn care people have tried, but customers want to see that you've done something. They actually like to see the cores.
A deep subject
Solid tines have another advantage — they can be used for deeper soil penetration and greater disruption of compacted soil. This may or may not be a priority. For example, most cool-season turfgrasses root in the top few inches of soil, so a relatively shallow aeration will suffice in many cases. But, “You should be getting down at least 2 inches,” says Landschoot. “If you're not taking more than an inch out of there, what good are you doing?” Thus, dry, compacted soil that prevents tines from penetrating very deeply can reduce the effectiveness of the aeration. This is where monitoring of soil moisture can help you make a good decision about when to aerate.
However, there are many instances where deeper penetration is critical, and solid tines are often the answer to this need. Stier uses the following example: “Let's say you have standing water on a field and a game in 24 hours. Long, solid tines can poke holes through the soil and temporarily help drainage.” Stier cautions that this may be only a short-term fix, however.
Another situation that may call for greater aeration depth is the presence of a cultivation layer, or plow pan. These compacted layers of soil have been known to develop just below the depth of aeration in turf that has been aerated at the same depth repeatedly for many years. Deep-tine aeration can alleviate this problem by disrupting the plow-pan layer.
Landschoot says that one of the advantages of many solid-tine units is that they can bring more brute power to bear on extreme compaction problems. He notes that Penn State athletic turf manager Bob Hudzik uses a solid-tine aerator at soccer goals. “The tines go in at an angle and then lift straight up to fracture the soil. Then he goes over it with a regular core aerator, and then he drags it. By the time he's done, he nearly has a fresh seed bed.”
Not all deep tines are solid tines; some coring tines are designed to penetrate soil deeply, as well. This may be preferable, depending on whether and how you can deal with the cores, and whether you are attempting soil replacement. Of course, if the latter is your goal, coring tines are the proper choice. Many units on the market allow you to change tines, permitting you to choose not only the depth, but also hollow vs. solid. Both types are available to reach a range of depths up to 16 inches or more.
The term “shatter tine” describes units that create the fracturing Landschoot refers to. These units employ additional movement of the tines besides a straight in-and-out motion. As a result, the soil around the tines fractures. This loosens a much greater volume of soil than hollow tines that punch clean holes. Solid tines are the type generally used for shatter tining. It is critical that soil is not too moist when using a shatter-tine unit.
Conversely, if you use coring tines, the soil needs to be moist. Gaussoin uses an analogy to illustrate why this is so. “If you take a wet wad of soil and throw it against the wall, it sticks. If you take a piece of dry soil and throw it against a wall, it shatters.” Likewise, soil that's too moist will not fracture during aeration, rendering the shattering action less effective. For this reason, some manufacturers offer units that allow the user to adjust the degree of shattering action according to which tines are installed on the machine.
Feel the power
A fundamental difference between aerators is whether the tines are powered. Almost exclusively, drum-type aerators rely on their own weight (which may be considerable) for tine penetration. Such units commonly include rollers or drums that can be filled with water for extra weight.
Cam, or piston, units are powered by a camshaft, which propels the tines up and down. The power may be derived from a PTO or from a separate engine.
The type of power source has several ramifications. For one, rolling tines enter at an angle, rock forward and then exit at a different angle. This creates a small amount of soil compression around the entry hole, especially if the soil is fairly moist. By contrast, most piston-type tines travel straight up and down. This allows the tine to remove the core cleanly. The force of their up-and-down movement also means they can penetrate drier, compacted soil more readily or drive longer tines deep into the ground.
While cam types possess certain advantages, drum types remain very popular for their own reasons. “Piston types are more expensive, there's another engine involved, and they're slower. But they also penetrate more. Drum types are cheap and can cover very large areas quickly,” says Stier. And as long as soil moisture is appropriate and penetration is deep enough to suit your purposes, the results are good. Drum types can be pulled by tractors or other equipment for larger areas, or they may be self-propelled, such as the popular smaller units that are well-suited for residential lawns. However, smaller piston units are available for lawn care, too.
A variety of options
Manufacturers have invented a range of designs to achieve the goals of aeration. Hydraulic aerators “drill” with water; “drill-and-fill” units use real (metal) drills to create holes and then re-fill them with the desired rootzone mix in one operation.
One of the newest innovations is high-pressure injection (HPI). These units have several uses, including soil injection of pesticides and even of grass seeds. However, simply running water through them creates tiny aeration holes that can break through layers and surface crusts. HPI units shoot water through nozzles at extremely high pressure, but in tiny jets. These are so small that they do minimal damage to turf and don't disrupt the playing surface. However, they also aerate less effectively than mechanical units due to the small size of the holes.
As Landschoot describes it, “It is technically aeration. Most agronomists would say using water injection has advantages, but not as a long-term substitute for coring. HPI units are good for times when coring may not be an option…during summer heat, or the middle of the golf season, for example.”
Gaussoin agrees, explaining, “HPI is a nice tool because superintendents can use them in the heat of the summer and they don't disrupt the surface. They can be used when other methods can't. They can't be used for soil modification, but they can give deep penetration.”
Similar to HPI are needle tines that some aerator manufacturers offer for summer use. They're similar to HPI in that they can open up turf somewhat, but without the more substantial disruption of larger tines.
Two more traditional types of “aeration” are spiking and slicing. These methods use a drum on which is mounted either spikes or blades. As the unit is pulled along the turf, the spikes or blades disrupt the soil surface. This is not what many people traditionally think of as aeration. According to Landschoot, “It does allow some soil aeration, but it's not a substitute for core aeration. But I think it has some advantages, like breaking up surface crusting.”
Apparently so. As Gaussoin observes, “Spikers and slicers were put on the back shelf 15 to 20 years ago. I see turf managers going back to them now because they are less surface-disruptive. Compaction is primarily in the top inch, so they have some use there.”
Aeration is a highly beneficial practice. According to Stier, “mowing, fertilizing and irrigating are the three primary cultural practices. For athletic fields, I consider aeration a close fourth. A good aeration program should help thicken turf, which should reduce weed pressure and herbicide use and improve stress tolerance in general.” Who can argue with that?
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