So why do we aerate and why now?

As promised in the last post, I will discuss the necessity and timing of aeration.  Let's first begin with a course update. 

Overall the course is back in top condition. Over the last week the crew worked tirelessly to get caught up on the backlog from aeration and the wet week that followed. 

The greens that had issues are recovering, albeit slowly. I am very impatient; I have to keep telling myself it has been less than a week since we discovered what was going on. I expect to see the rate of recovery to pick up over the next few days. I held off fertilizing them right away and made sure the plants were strong enough to take on the pressure of being fertilized and the associated extra growth; otherwise they could overfeed on nitrogen and die off. 

They were fed with biostimulants, calcium and other micro-nutrients first to prepare them for the larger fertilizer applications on Thursday and Friday. It takes a day or two for the plant to take the fertilizer up and for it to have an effect. The pick up in growth this morning shows that they are reacting to it and starting to actively grow. The new growth is pushing through moving the brown tips upward. The amount of green tissue starting to push through can be seen in the picture below and if you move the sand around, more plants can be seen ready to break through. 

Each days mowing will take off the brown tips, so it eventually fades out as the green leaves grow. The two pictures below are from 1 green; the top one is Monday around 11am and the lower one from the same angle at 11am today. The recovery, while it still has quite a bit to go, is notable even after 4 days. 

The greens were also seeded this week. We used Job Saver tines on our aerators (pictures below). These little tines are designed for overseeding into an existing canopy. They make shallow holes for the seed. The greens were then rolled essentially planting the seed to protect it and keep it warm and moist so it germinates. Bentgrass seed germinates relatively quickly so I expect to see some more green fuzz popping up by the middle of next week to help speed up the recovery. 

We will continue to fertilize and push the growth, along with lowering the height of cut. We have been lowering the height daily for the last few days with no negative effects. Once the lowered height reaches the sand we will slow the rate at which we lower the mowers. The greens need another very light topdressing to get them perfectly smooth. While they are fine right now, once the mowers get back to cutting at 0.1", it is essential they are perfectly smooth or the greens will be damaged from scalping. The picture below shows one of these imperfections; it is the darker green spot in the lower middle. If it is left un-topdressed the mowers will scalp it leaving a bare spot. 

When we topdress, depends on the health of the plant as we do not want to do any more damage. The topdressing from aeration has been worked in on most of the greens so adding a little more will not cause an issue.  It is essential however that the plants are healthy enough to withstand the stress from the broom. With it being a light topdressing it is easily worked in so, again, it is not as much of an issue as it was during aeration when the holes had to be filled. We plan to work it into the schedule as soon as the turf is healthy enough for us to do so.

So, the answers to the title questions:

The main benefit of an aeration is to provide air and water channels for the roots. The roots are a vital component for the plant as they are the location where the plant takes up nutrients and water. The longer and healthier the roots are, the healthier the plant and the greater it's ability to withstand stress. There are numerous ways to aerate; from solid tining (sticking a fork in it!); to hollow tining (removing soil); water injection (creates tiny channels); deep and shallow tines (varies on how deep you need to go); drilling; slicing and some more I'm forgetting. There are various methods to accomplish these procedures also, each having varying degrees of surface disruption and area disturbed beneath the surface. For example, a spiker (below) leaves a small triangular hole that provides a lot of area for air exchange but it is not a deep machine; it can tuft the surface so it would not be as acceptable as a small needletine, which has less surface area but penetrates deeper and leaves the surface intact.

Most of the deeptine machines also kick as they move through the soil. This action helps fracture the soil and loosen it, reducing compaction and creating more air/water pockets for the roots. The Wiedenmann (below) we used on greens was adjusted to minimize the kick as it was in sand;  the main goal with it was to leave deeper channels through the mat layer.

These methods of aeration also help with soil issues. If a soil does not drain well (like a native soil green), the holes can be filled with a better draining material, improving the composition of the entire profile. 

The hollow tines remove material from the soil. If the goal is to modify the soil, removing a core is better than pushing a hole into the soil, which can cause compaction at a deeper level. Hollow tines also help remove thatch, which is the organic material plants create. Creeping bentgrass is a big thatch producer as it has stolons (runners) that are above the soil. As the plants grow this runner level gets thicker and becomes spongy. On a green it creates a lot of issues from both a golfer and maintenance prospective; the greens are soft, hold water, difficult to cut (as the mower can dig in and scalp),  can dry out quicker as thatch can become hydrophobic, and numerous other issues. Removing it is essential to have quality greens, especially if they are bentgrass. Physically removing the thatch greatly helps in keeping it in check. In most cases it is recommended to remove 20-25% per year, just to keep up with the production. That is over 11 triaxle loads of material per year on the greens at LedgeRock alone! Skipping an aeration can be very difficult to recover from when you consider the volumes that are involved.

Topdressing helps reduce thatch also by simply burying it, which dilutes the amount of the organic material in a given volume. As I mentioned in an earlier post, topdressing also keeps the putting surface true and smooth which helps increase green-speed. Topdressing also can be beneficial when drainage is an issue. As the sand layer builds up it creates a free draining layer for water to move through to drainage channels, which are essential so the water has somewhere to go.

Diluted thatch (mat) and topdressing layer on a green

And finally; why do we do it when we do?

There are a number of factors that influence the timing of aeration. Non-evasive aeration, like needletining, can be carried out pretty much anytime as it does not affect the playabilty of the course; however hollow tine aeration needs to be carefully planned. 

Recovery time drives the timing. The turf should be aerated at a time that minimizes the down time for the course. On average a course can be fully back in play within three weeks from the start of aeration. This period depends on how aggressive the aeration was and how long it took to complete. Sometimes the process itself can take 4-5 days but full recovery should be within 2 weeks from completion provided the weather is conducive to growth. 

Here at LedgeRock we used to aerate as soon as we could in the spring; We usually had all the greens completed by the end of March, which was ideal as it was out of the way and all resources could be directed to prepping the course for the season. The downside was that it took until late April to early May to heal. This is due to the fact the soil temperatures are not consistently warm enough for turf growth until that time. As discussed back in the spring, the slow warm up delayed recovery even further. The decision was made about 4-5 years ago to move our spring aeration to mid- April, when the soils usually start to warm up, so that the course would be playable longer if March and early April were nice. By doing this, recovery time is usually in the 3 week range as opposed to 6-8 as it was when we first started. 

For a similar reason, it was moved to an earlier date in the fall. It was scheduled right after Labor day, however, the temperatures started dropping and recovery slowed. In 2007 there were traces of aeration holes all winter, right up until the spring aeration; almost 7 months! Admittedly they are not all great months for golfing but had they been aerated earlier, they would have been fully healed by mid - September, leaving 6 months of quality surfaces.

The USGA also brought to my attention that moving these dates would greatly reduce Poa annua encroachment. Poa annua is a winter annual which likes cooler weather to bentgrass. By aerating earlier, the bentgrass is more competitive and can close up all the holes, not leaving any bare areas where Poa can get established. This is why you may see courses that are predominantly Poa, aerating when the temperatures are cooler. Since Poa is not as strong of a plant as bentgrass, the cooler temperatures also help it recover from the stress that the aeration procedures put the turf under; Poa would be more likely to die during the summer heat.

Of course you can run into issues if the weather changes a little, as happened to us this year; but the average pattern has to be used, otherwise there never would be a right time. 

This USGA article is a nice resource on the timing of aeration.

Have a great week and enjoy the beautiful weather!