Making a Thatch Sandwich - Part 2

I have just top-dressed the lawn. If you read this, you will see why:

We have seen that reducing lawn thatch can be achieved by:

• minimising thatch and mat production
• enhancing the natural breakdown of thatch and mat
  

MINIMISING THATCH AND MAT PRODUCTION

• remove mower clippings
• avoid high doses of nitrogen feeds during first half of season - slow steady growth seems best
  

I don't want to deal with cutting and feeding here. These have been referred to elsewhere.


ENHANCING NATURAL BREAKDOWN OF THATCH AND MATT

• reduce acidity
• use organic nitrogen feeds
• improve aeration
• control water content

Natural breakdown is undertaken by micro-organisms in the soil. Enhancement of this process is achieved by producing an appropriate environment.

acidity
We have already seen that the lawn has been limed to reduce acidity.

organic nitrogen feeds
Using nitrogen feeds in ammonium form (and feeds which can be easily converted to ammonium (e.g. urea)) rather than in nitrate form greatly helps the build up of micro-organisms.

aeration
Aeorbic micro-organisms (which are beneficial to our purpose) need oxygen to function. Pricking the turf facilitates this. Tining and hollow-tining has the same effect.

water content
Micro-organisms need the thatch to be damp if they are to break it down. They cannot work on dry thatch. Pricking also facilitates this. Top-dressing also helps to prevent the thatch from drying out.


TOP-DRESSING

Making the sandwich
Top-dressing involves covering the thatch surface (after raking) with a layer of soil - mixed with sharp sand and organic matter - which is worked into the turf and levelled. This helps prevent the thatch and mat from drying out, allows it to be attacked from both top and bottom (since it contains micro-organisms), and levels out any hollows.

Effectively, a new false soil layer is created, kept open by the sharp sand (not builders' sand). The organic matter (use of this is optional; it helps improve soil structure) can be garden compost sieved through a 1/4 inch sieve. The soil can be garden soil, also passed through a 1/4 inch sieve. The mixture is applied at the rate of about 1 to 1.5 kg per sq metre (about 2.5 to 3.5 lbs per square yard). Apply two or three times as much if you have hollow-tined.

Although it is easy to buy top dressing, it is better to make your own if possible. This way you can adjust it to suit your lawn conditions. For example, for a heavy, poorly-drained clay soil, you could use about 75% sand. On the other hand, a sandy soil might only need about 20% sand. It's up to you. You have much more control.

To level the surface, drag a straight piece of 2 inch by 4 inch timber over it, once you have applied the dressing.

• If your soil is really heavy, hollow-tine or deep-tine first, then brush sandy mix into holes.

• Always make sure that the dressing is worked in: Do not leave it on top of the grass.

• This job is best done when both the grass and the dressing are as dry as possible.

Top-dressing not only levels the surface and improves breakdown of thatch and mat; it will stimulate the grasses to produce new side shoots, thus thickening the turf.