preparing the seedbed

Preparing the Ground

Proper preparation of the ground for a new lawn will reward you with years of problem free lawn care, easier mowing and a beautiful healthy lawn

If the area already exists as a lawn or has plants in it kill the whole area first if you have time. This will reduce the occurrence of future weeds and weed grasses in your new lawn. Use glyphosate as this degrades on contact with the soil leaving no harmful residue. As with all weed killers this only works when things warm up so timing is between April and September. Once everything is dead, perhaps after a couple of weeks, you can proceed. If you are starting preparation before April you are best to avoid using weed killer.

Whether or not you have sprayed strip off any turf with a spade, turf iron or petrol turf cutter available from Hire Shops. This may seem unnecessary hard work particularly if your next step is to dig or rotovate the area. Unfortunately, existing turf will not break up readily thereby making it harder work to rotovate or dig. In addition the old turf will cause a bumpy lawn containing air pockets which will then increase the bumpiness over time. So, remove the old turf and if you have a place to store it then do so as it will eventually rot down and make a great compost or top dressing later on.

At any stage during lawn preparation be prepared to pick up or rake out stones and debris such as roots. The quality of lawn you are constructing will determine how far you go with this process. And if perfection is your goal then consider bringing in double screened (1/4” sieved) sandy loam topsoil for the top few inches.

If you have had a soil test done now is the time to plan and order those amendments that you are going to make. These may include:

  • Addition of lime to highly acidic soils
  • Addition of organics and humus to poor, very sandy or heavy clay soils
  • Addition of loam top soil to sandy soils
  • Addition of sandy loam top soil to light clay soils
  • Addition of loam top soil if the depth of existing soil is less than 4"
  • Addition of pre-seeding or pre-turfing fertiliser such as Lawnsmith® STARTER Lawn Feed

Caution: Sand or sandy loams mixed into very heavy sticky clay soils can set like concrete so if you are trying to amend a heavy clay soil it is best to remove it and replace it with an appropriate sandy loam down to a depth of at least six inches preferably a foot. If the bed of soil below that is still heavy clay then go further or call in a professional to lay drainage.

Double dig or rotovate the soil to a depth of 6 to 8 inches (15 to 20 cms). Less depth, say 10cms is okay but if you’re going to the trouble of digging it up you might as well do it thoroughly. Rotovate at least twice and if the depth and tilth are not reasonably uniform repeat the process again at right angles if possible or use a garden fork to break up any large clods and make the area more uniform. Your fertiliser should be incorporated at the end of this stage.

Heavy soils will break up more easily when they are on the dry side which will also prevent them from smearing on the rotovator blades. If this happens stop and let the ground dry a little otherwise you could be causing drainage problems later on. Conversely, sandy soils may well need some moisture to maintain the texture. Friable is the word used to describe the result we wish to achieve; a crumbly soil that is neither great clods of clay nor a loose sandy beach!

Soil Amendments

If you’re adding lime be careful not to overdo it. Making the soil for an ornamental lawn too alkaline is detrimental to the finer grasses and will promote weeds and weed grasses. The amounts should be given to you by the laboratory that did your soil analysis. When adding lime do so as evenly as possible otherwise you will have different pH values and therefore different growth properties throughout the lawn. Use ground limestone or dolomitic limestone only.

When adding soil or organics do so in stages and NEVER layer one soil on top of another without blending by digging or rotovating. The greater the quantity or depth of amendment will affect the steps you will take to incorporate it. This will also affect the pH of the finished job so it’s worth getting a pH for the new soil. If you're adding organic matter the best is completely rotted none animal manure or humus.

Adding 6” or 15 cm of new soil. This is unusual but may be required for very heavy clay areas.

  • Split quantity into three lots
  • Dig or rotovate lot 1 down to 20cm deep
  • Add lot 2 and rotovate down to 15cm deep
  • Finally add lot 3 and incorporate into the top 10cm only

WARNING: After each addition and blending of soil you should consolidate the layer by treading or using a medium roller over the entire area. This removes air from the layer preventing settling later on. You can only affect to about 5cm deep when treading or rolling which means it needs to be done as the layers are put down. See TREADING in the 'Penultimate Step' below

From this you will see that there is a thorough mixing of the old and new soils, the old soil has been well broken up and the soil profile is light and freely draining at the surface with the moisture holding clay layer deep down. This is perfect for grass health and to promote excellent rooting.

For quantities that are less than this incorporate as follows:

  • For 4” or 10cm of new soil split into 2 lots and start as for lot 2
  • For 2” or 5cm of soil incorporate into the top 10cm only
  • For organics or lime incorporate at 10 to 15cm as for or with lot 2

Cleaning the Seed Bed

The process of tilling the ground will have brought weed seeds to the surface which will germinate into your new lawn. You can do several things at this stage to reduce the impact:

  • If you’re laying turf, weed seeds will not be too much of a problem
  • If you’re seeding, increase the amount of grass seed to out compete potential weed seeds
  • If you have time to leave the prepared ground for a while to allow weed seeds to germinate then do so. You should then spray the area with a glyphosate weedkiller a week prior to seeding

Using Sand

The addition of sand or sharp sand to lighten heavy soil is possible but it does require to be very well blended with your existing soil. Heavy clay soils benefit the most from the addition of sand but they are also the hardest to blend. River sand is the best sand to use and builders or coastal sand a no-no!

I often see turfers using sand layered at about 1” deep on top of prepared ground prior to seeding or turfing. This is done supposedly to add a smooth finish and improve drainage but can have long term negative impacts. In my humble opinion this does nothing for drainage as drains need to be at the bottom not the top!! The sand may well affect the grass as it's often builders sand that is used (contains lime) and at best is a poor substitute for a properly prepared and smoothed surface. Admittedly, heavy clay soils that are wet are the devils own job to level and smooth so timing, hard work and proper amendment of the soil is required, not a layer of sand!

The Penultimate Step

This final stage completes the preparation and readies the lawn area for sowing grass seed or laying turf.

Start off by raking the area to a reasonably smooth level. I like to use a landscapers or hay rake for this because the flat back allows me to push and move soil around.

TREADING: Next comes the old fashioned art of ‘treading’ or ‘heeling’ the soil surface. It takes time but pays dividends in giving a flat firm finish. This is what true professionals will do as it is the only way to squeeze out air pockets and remove any likelihood of sinking later on. It’s the equivalent of kneading dough to make bread. With most of your weight on your heels just shuffle and tread up and down the area moving your feet about half a foot length each time. You need to tread every square inch of the prepared area so make sure you’ve got plenty of Radox because you’ll need a good soak afterwards!

Once you’ve trod the area start raking again to reduce bumps and fill depressions. If you’ve got the energy and inclination tread again in a different direction, rake to level and repeat one last time. Repeated treading will be required for an ornamental lawn as will the use of boards, levels and string to get a perfectly flat finish.

If you’ve forgotten to add your pre-seeding starter fertiliser you can add it now or just prior to seeding or turfing.

The final step is to build up some moisture in the soil if things are dry. This is crucial if you are creating a lawn from seed because you can only water lightly and gently once the seed is in otherwise you’ll start washing it out. Do this a few days before seeding so that the surface is dry enough to rake without sticking to your shoes during the seed sowing stage. Watering will also settle the ground so if you haven’t heeled it properly it gives you an opportunity to correct it before seeding or turfing.