Preparing the soil for grass seed

Following on from our grass seed selection blog, here’s the lowdown on preparing the soil for grass seed.

So you’ve decided to sow a new lawn from grass seed. Perhaps you’re replacing an existing lawn that’s become tired and ugly, or perhaps you are redesigning your garden. No matter what the reason, the secret to a beautiful lawn lies mostly in the soil.

Soil science is very much in its infancy. In fact I often think that we know more about outer space than we do about the ground beneath our feet. What I have learned in years of greenkeeping training and experience is that the health of your soil really does impact the health (and management) of your lawn.

To successfully grow a lawn from grass seed the soil must be

Well drained
Nutrient rich
Nicely aerated
Have a good population of worms, beetles and microbes
Ideally free from perennial weeds

Nice crumbly topsoil like this is ideal for sowing grass seed. If the soil in your garden is sticky and clay-like try digging in lots of compost to help improve the structure.

In this article we’re looking at how to ensure that your soil is in tip top condition before sowing grass seed.

Improving your soil for grass seed

First, treat the weeds

You’ll never get rid of weed seeds in the soil but in most cases, once your grass seed germinates, a nice thick sward of grass and regular mowing will sort out any cheeky annual weeds. The ones that you really don’t want popping up all over the place, are the perennials. Particularly not weed grasses or things like nettles, docks, dandelions and daisies. All of these need to be cleared from the area.

Before you start stirring up the soil for grass seed, use a systemic herbicide to kill the leaves and roots. The keyword here is systemic. These are the weedkillers like glyphosate (trade name) Roundup that circulate through the plant’s whole system and ensure that nothing is left alive. Beware the cheap alternatives that just turn the leaves brown but don’t affect the roots.

To make life easier when you come to clear the area later – mow it nice and close before applying the weed killer – but be sure to leave enough vegetation to absorb the herbicide.

When applying sprays, always wear the right protective gear and follow the manufacturer’s instructions to the letter. No spraying on windy days either – a little bit of spray drift can decimate your prize plants.

Glyphosate will take 3-4 weeks to work properly, so be patient.

If you’re not a fan of chemical treatments, you can use a turf cutter to take away most of the vegetation and then dig (not rotovate!) the area to remove rogue roots. Rotovating is great once the soil is weed-free. However, if you’re not careful you can chop up and spread the roots of weeds and end up with a great big mess.

Next, remove the debris

If you’ve used a weedkiller, you’ll have brown fuzz all over the surface of the lawn. Now there’s two ways of approaching this.

You COULD, remove all of that debris to give you a nice clean surface. Certainly if it’s very thick, you’ll need to do that.

If the soil is very compacted, I’d also recommend rotovating or digging over the area. You’ll be opening up the soil structure. And by incorporating the dead material you’ll help to support those all-important soil microbes.

How do you know if your soil is compacted? Try pushing a 15cm screwdriver into the soil as far as it will go. If it doesn’t slide in like a knife into a jar of honey – the soil is compacted.

Method 2 – my preferred method

Soil ecosystems are very complicated. Different critters live at different soil depths and when you turn the soil over, you literally turn their lives upside down.

When I’m re-seeding an existing lawn and I know that the soil is not severely compacted, I’ll use my scarifier to remove the old, dead lawn.

It takes several passes, working in a different direction each time and gradually dropping the blades. But this way doesn’t give me back ache and I feel that it doesn’t have an adverse effect on soil microbes.

Follow up with by aerating the soil and then either rake the cores off or scarify once more to crumble them up.

Creating a level seedbed

Humps and hollows in the lawn make mowing tricky. So now is the time to address that. By taking time to level the seedbed, you’ll make your life easier in the long run.

If you’ve dug or rotovated the area, use a landscaping rake to break down any large lumps and create a tilth that looks a bit like the top of an apple crumble. Use your feet to firm the soil for grass seed (you don’t want it to sink or settle once the seed is in) and then rake again to loosen the surface.

If you’ve used the scarifier method – and you’ve done enough passes so that you can see bare soil, you should be OK. Double-check the compaction and ensure that the surface is nice and loose. Now add a layer of topdressing to create a level surface. This is also a good time to apply a pre-seeding fertiliser.

As a greenkeeper I learned lots of tricks to help me level a lawn and I’ve shared them with you in the video below.

If your lawn is reasonably level, you can sow the seed before topdressing and then just tweak. Any big hills and hollows do need to be addressed before the seed goes down. It’s time consuming but well worth the effort.

Perfect soil = perfect lawn