Question
Kenneth

I have inherited a large but untended and uneven lawn, that has 25 years of compaction and in some places is hard as concrete.

I have bought a tining tool and in the autumn walked up and down the compacted areas taking tines out of the turf (every 3 inches) and discarding them.  I did not, however, fill in the holes with sand etc, which is what everyone told me to do.  Have I negated the effect of the tining?  And what do I do between now and the spring?

I have also bought a scarifier attachment for my petrol mower, but I suspect that I should not use it before April?

For info, I live in London (rain, cold etc) the lawn slopes slightly, and the soil under the turf is probably london clay (as in the rest of the garden).

Thanks very much in advance for your help,

All the best

Elliot Renton

Answer
The use of a tining tool is highly recommended. It is also sometimes commonly referred to as core aerating. The removal of cores of soil will loosen the soil around the roots which will permit roots to grow deeper. Oxygen, water and nutrients (fertilizer) can reach the root zone and carbondioxide can escape. The decomposing cores on the surface of the lawn will also invite microbes to the surface which will help break down thatch. It is a very beneficial horticultural practice.

Sand is not required. I know that most sports fields will topdress with sand, but it is not necerssary. The core holes will eventually close but that is ok. The grass has still benefited. You can repeat the core aerating annually for best results.

De-thatching /  scarifier is really only required if you have a thatch problem. Thatch is partially decomposed rhizomes, roots and crowns of grass which compact together between the green part of the grass and the soil. If you look at one of the cores of soil you may notice an 'off-color' layer 1/8 - 2" thick between the green and soil layers. This is thatch. It has a 'felt' (fabric) feel to it. A moderate (less than 1/2") layer is beneficial to the lawn, but more will prevent oxygen, water and fertilizer from reaching the root zone. In that case you can core aerate or scarify (de-thatch) the lawn.

I much prefer core aerating (tining) as opposed to scarifying. Scarifying do not provide the benefits of deep cultivation and it does not loosen the soil the same whay tining does. Scarifying is also more damaging to the lawn compared to core aerating. If you have a very bad thatch layer then de-thatching (scarifying) may be required, but in most cases core aerating (tining) can be just as beneficial, if not more.

Thatch can be difficul to see. The best is to dig up a core of soil and gently break it apart. The thatch will look like dirt, but it is not dirt. It is a layer of organic material (roots, rhizomes and crowns) compressed at the top layer between the soil and the grass tops. If you have ever seen peatmoss sphagnum then this is how it would look.. dark brown and somewhat soft to press with your hands. When you pull the core apart the clay will lump together and not easily come apart. The thatch layer will pull apart in 'threads'. A moderate layer is good, but too much is not good.

Just a piece of info:
contrary to (much) advice, clay is an excellent surface for grass to grow. It retains moisture, has a high CEC (ability to hold on to and transfer fertilizer to the grass), and it reduces polution. If you use your tining equipment once per year you will solve the main issue with clay: compaction.

Good luck.


Here are some pictures of thatch (the first two are a bit misleading.. normally thatch is not that easy to see. The 3rd picture is more representative of how thatch looks. Feeling thatch between your fingers is the best identifer) :

http://www.extension.umn.edu/yardandgarden/YGLNews/images/thatch.jpg
http://hflp.sdstate.edu/images/turf%20with%20thatch2.jpg
http://ianrpubs.unl.edu/horticulture/graphics/thatch1.jpg
http://www.urbanext.uiuc.edu/lawnchallenge/images/photo5-1.jpg

Illustration of the benefit of core aerating (tining) :
http://members.aol.com/turfman100/turf1.jpg