I have an uneven back garden which i now want to level. There is also a lot of old brick and blocks of concrete in the garden which are ready to be skipped.
I spoke to a builder and he recommended using the old brick etc to level off the garden and then place topsoil and grass seed over that.
Firstly is this a good idea and secondly how much topsoil would be needed on top of the hardcorde to give me a good lawn?
Whether it's a good idea or not is down to whether you want a good lawn over time or whether you want a possibly waterlogged in winter (depending where you live), drought sensitive, patchy and bumpy rough area of grass.
You should remove and skip bricks, lumps of concrete, rocks and the like from the area you want to turf first, then prepare the area in order to lay turf. As you level the soil, you may find you need topsoil if the levels are too low against an existing path or patio. I'm offering no advice at this stage about proper preparation for laying turf because I'm not sure where you are in the world, what type of grass you'll be using and whether you want such information.
Builders frequently bury their debris in gardens - there are many new build houses up and down the UK which look like they have neat, turfed gardens and (usually) a tree, which then becomes a big problem over time, often within the first year - the lawn becomes patchy, sinks in some areas, dies out in others and so on; unfortunately, the solution is to dig it all up, remove the offending concrete, bricks and anything else they've buried and start again.
The fact is, each tuft of grass in turf is a plant, and plants grow better in good soil, and just because it's grass, it doesn't mean it won't mind being grown over lumps of debris, with or without topsoil placed over. Often, rubble in the soil aggregates over time and causes a virtually impenetrable layer, causing significant drainage problems, so that's one good reason not to do as the builder says. And another is, don't ask a builder for good advice about anything to do with plants and lawns; I'm pretty sure you wouldn't ask a gardener or horticulturalist how to fit a kitchen or build a house or something similar, so keep the builder in reserve for his area of expertise - building.
Keeping the builder away from the landscape is perfect advice. LOL!! Truly have to see a picture of your entire lawn area/site. Dealing with buried concrete and bricks is tricky. Depends on how much was dumped, and if there was decomposable material like wood involved. If there is wood beneath when it decomposes it will cause sinking of the surface to fill the new space.
If you find when you dig a 'test hole' that it appears to be a large, deep hole filled with big chunks the original builders have created for you a 'perched water table". Simply, all the small pore spaces of the topsoil will have to be completely saturated before any downward drainage can make its way into the chunks of stuff. (Same with rocks at the bottom of potting soil in a potted plant, a no-no).
No lawn should be perfectly flat. Ideally, 1-2% slope is indicated for lawns. You don't want water sitting on top of your lawn. Because of the perched water table situation this slope will be even more important to manage drainage. You can dig dry well 'trenches' along the easiest side of your lawn to catch and allow water to slowly filter through the soil or use Perforated drain pipe to carry the water to an area that with a single dry well. You do not want water draining off your site onto your neighbors. Big no-no for all kinds of reasons.
I'd pull up all the shallow concrete and bricks for sure. Are you able to talk with the original builder (don't tell him I said he was an idiot) grins! He could tell you how deep, the type of debris he threw in the hole, otherwise get ready to dig a deep hole (no more than 3') to get an idea of how deep this mess is. Below 2-3 feet the debris will no longer be an issue unless you've got decomposing wood. A few chunks here and there within this man made soil profile of 2-3' below the surface is no big deal, but if it is solid, bummers.
There will be suitable drainage if you can clear at least 12 -18" of debris from the surface AND your is lawn sloped (Rise/Run=Slope). It used to be 1% was enough when people erroneously insisted on having a 'putting green' of short grass. Now we know that 3" (cool season grasses) is as short as residential lawns should be mowed. Seriously, not 2 1/2" but 3"!! Critical for a healthy, vibrant, weed free lawn.
Bring in good topsoil already mixed with decomposed organic matter. Square footage of area divided by 81 gives you yardage of soil for that area to make 4" deep. You should need only 2" on top of your existing 12-18" if soil... so divide yardage by 2. Grade (try to rent a grading rake which is 3' wide, much easier and better to grade soil), then roll baby roll! (rent a water filled roller)...you'll easily see the lumps and divets. Go grade some more and roll again. If there are still lumps and holes, grade and roll again.
My advice is to use sod (once laid roll one more time, you can fix any depressions at the same time). The next best is to hire a spray seeding company. They've the best seed mixes and includes water retention mulch/proper fertilizer for baby grass. The worst way to start a lawn is from owner seeding. Grass will compete with weeds from the beginning. If you chose this you need to use a mechanical spreader. Do not throw seed by hand! All that work and to throw seed or fertilizer by hand is just sad.
An established grass crop mowed no shorter than 3" is able to out compete as well as shade the soil to discourage weed seed germination. Once the sod has put roots down into your ROLLED soil you can then start mowing (less than a week, test by pulling up on the sod and it should resist). Once your lawn is established (2 or 3 mowings for sod) you will then be able to start training the roots to grow deep to be drought tolerant and save on the water bills! Water deeply and allow to dry before watering again. We've got lots of lawn advice on this site and you should read all of them to understand this creature you want to create that is called a lawn. And don't use fast release fertilizers by Scott's or Ortho. There are incredible organic fertilizers these days that are slow release and last longer and are far better for the health of your lawn. We can help save you money and have the best lawn on your block!
