Soil preparation for Empire Zoysia

dantab · Mar 13, 2017 2:41 pm

Hi All

We had 120sqm of Empire Zoysia laid on the weekend.

Our landscaper said our soil was good so we didn't do any soil preparation other than leveling the area.

However, before we laid the lawn it became apparent the soil wasn't that great. It is full of rocks and building debris. It is also very hard / compacted. I know this because I was trying (with limited success) to dig out trenches to put in a subsurface greywater system (which will be supplemented by an above ground irrigation system). I've linked to some photos of the soil and debris I removed when trenching.

Some additional background to the area where the lawn was laid is that there used to be a concrete pool there which has since been smashed and buried. I'm told the remains of the pool should be about 1.5m below the surface. I'm not entirely sure what the area was filled with but the soil appears to contain a decent amount of clay given its firmness (which wouldn't be unusual given we are in the Perth hills - Kalamunda).

Anyway, I'm seriously considering pulling up the lawn this coming weekend and doing a proper soil preparation and then relaying. One option is to remove 250mm to 300mm of soil and bring in all new soil. If we do this what should we get to fill it with? Alternatively, have we got any options for working with the existing soil given the rocks / building rubble? Or are they not a problem at all?

https://flic.kr/p/SjyS2S
https://flic.kr/p/SUopMt

dantab · Mar 26, 2017 9:34 pm

Hi All

An update and a request for help!

Last weekend we removed about 200mm - 250mm of soil. After this, the bobcat cut into the remaining soil (which was very compacted) and we mixed in humus soil conditioner, zeolite and perlite. We then replaced the removed soil with "Magic Lawn Dress' from Bio-Organics (http://www.bioorganics.com.au) (see description below) and mixed some zeolite and perlite into this.

Product Description:
Bio-Organics’ Magic Lawn Dress is a blended Organic Soil tailored to create a healthy surface spread for all types of lawn. Predominantly made with our fully composted, organic Soil Enricher, it is bulked with quarry-sourced Lawn Sand to encourage quick root development to take advantage of the nutrients within the compost.

Product Composition:
66% Soil Enricher (screened -10mm)
33% Lawn Sand

Our landscaper then levelled the soil, compacted the soil (but only about half of it before laying the lawn), then laid the lawn and compacted the lawn. All this was done with the soil being dry and using a small compactor from Bunnings.

A week on and, as you can see from the photos and video, some parts of the lawn are extremely soggy and just collapse when you walk on it (the photos/video were taken about 2 hours after watering).

https://flic.kr/p/TdC8FL
https://flic.kr/p/T5PbYZ
https://www.youtube.com/watch?v=SvWAEs3opnQ

Is this just an issue of the soil not being compacted sufficiently, is it a drainage problem or is there something else going on here? I know the water table is high in this location, there is an old 'smashed up' concrete pool buried underground and the soil they filled the pool with appears to have a high clay content and was very compacted.

I think I need some help from a professional (no disrespect, but my current landscaper isn't up to this job). Can anyone recommend someone in Perth who can help?

TheGardenWhisperer · Mar 26, 2017 11:36 pm

I would hope the pool had been modified with large holes cut to ensure drainage.
Otherwise it becomes a pool again, or a bog.

dantab · Mar 30, 2017 3:09 pm

The Garden Whisperer

I would hope the pool had been modified with large holes cut to ensure drainage.
Otherwise it becomes a pool again, or a bog.

The previous owner said the old pool was all smashed up before they filled in the area so I don't think the pool is the main source of the problem.

As an update, I have cut back the watering to 2 min, 3 times per day and the area has firmed up substantially.

A few people have commented that the soil we added has too much organic matter. The topsoil we added has 33% sand and 66% soil enricher / organic matter. Is this an appropriate ratio for the lawn?

I think the main problem is that original soil below the topsoil (approx 200mm - 250mm) does not drain very well. I'm hoping the organic matter overtime will actually help improve this.

Skinah · Apr 02, 2017 8:24 am

Organic matter is like a sponge. Takes heaps of water to get the water down deep iF
It is dry AND ages to dry out if it is wet. If you have damp ground then stop watering you don't need more.

I don't believe u can have too much organic matter so long as it has had time to compost down and stop producing heat. Stick your hand in after it drys out to take a temp reading. You will find the organic matter as it breaks down further is going to make your soil slump, some top dress with compost or good soil each year. Keep the soil below the height of paths as the grass adds height.

TheGardenWhisperer · May 01, 2017 12:09 am

dantab

The Garden Whisperer

I would hope the pool had been modified with large holes cut to ensure drainage.
Otherwise it becomes a pool again, or a bog.

The previous owner said the old pool was all smashed up before they filled in the area so I don't think the pool is the main source of the problem.

As an update, I have cut back the watering to 2 min, 3 times per day and the area has firmed up substantially.

A few people have commented that the soil we added has too much organic matter. The topsoil we added has 33% sand and 66% soil enricher / organic matter. Is this an appropriate ratio for the lawn?

I think the main problem is that original soil below the topsoil (approx 200mm - 250mm) does not drain very well. I'm hoping the organic matter overtime will actually help improve this.

TheGardenWhisperer · May 01, 2017 12:11 am

Not sure what's going on with my quote, so here's the reply

You shouldn't be watering that often.
Even if you were in Perth, we can water 2 times a week and with good soil prep, that's cut to once a fortnight. If you are in the Mexicos (Eastern States) it certainly won't need much, especially at this time of year.

It's not too much organic material.

I'd still check the pool isn't still there.