How To Lay Mulch Over Grass {Step-by-Step Guide}

If you’re wondering how to lay mulch over grass properly to kill the grass and suppress the weeds underneath, this guide will explain the best way to do that step-by-step.

A mulched and edged flower bed of various annuals and perennials growing in the summer.

Before you put in that veggie garden or flower bed, you will want to lay down mulch — but you need to do it the right way to avoid headaches next year.

This article discusses mulching as a way to suppress grass and weeds before putting in a new vegetable garden site, raised beds, fruit orchard, permaculture food forest, or decorative flower bed.

If you’re specifically interested in mulching as something to put on top of your soil in beds after planting to protect and nourish the soil your veggies, fruits, trees, or flowers are growing in, check out my article series on the topic including: the best mulch for an organic vegetable garden, the best mulch for fruit trees, and you may also want be interested in how to shred leaves for mulch as leaves are a popular alternative to cardboard for sheet mulching.

Why Put Mulch Over Grass

Mulching is the one of the most important things you can do in your garden.

Mulching retains moisture, protects your soil structure from erosion and nutrient loss, and keeps weeds and grasses at bay.

It can make a flower bed or garden site look neat and tidy while also decreasing maintenance activities like mowing and weeding.

Can You Put Mulch On Grass?

You can put mulch directly on grass — but it would be a waste of your time, as mulch alone is not enough to kill the grass and weeds. They would come through with a vengeance and you would ultimately waste a lot of time controlling that every year afterwards.

Similarly, you should not put down mulch on tilled bare soil either.

That’s what we found had been done with the flower beds on our new homestead, and the mulch was simply nowhere near enough to have anything but the bare minimum of effects.

Before you lay down mulch, you need to lay down weed suppression barrier materials.

Trust me.

Will Mulch Kill Grass Beneath?

A weed suppression barrier (more on options further down) with mulch on top will kill grass, weeds, and stop weed seeds from germinating.

While it can take a while to kill the grasses and weeds, and some maintenance will be required, that maintenance will be less and less with each passing season.

Yes, you can plant through the weed barrier you choose.

Will Grass & Weeds Grow Through Mulch?

The first year or two you should expect to see the most amount of grass and weeds poking through your layers of weed barrier material and mulch, but it will become less and less with each passing gardening season.

What Is The Best Time To Mulch Over Grass?

You can lay mulch over grass and start preparing garden beds anytime you want.

Ideally, this will be done in the autumn when grass and weeds are already going dormant and dying off. The work is easier at that time.

For a vegetable garden build, this also gives you time to start building organic matter into your soil or growing medium.

But it really doesn’t matter. We just lay down cardboard sheets and mulch this early spring in our new annual vegetable garden bed because this was the time we had to do it.

How to Lay Mulch Over Grass (Step-By-Step)

Here is how you lay mulch over grass for the best possible results. If you want more information on how we prepared our own raised bed garden site, this article discusses that along with what to put underneath raised beds.

See Also:

Mow Down The Grass & Weeds Or Remove The Sod

The first step is to mow the area on the lowest setting on your mower.

You don’t have to completely remove the sod by the way, you can always just edge the area and leave a strip bare if you’re going for that crisp edged look. You will have to spend time weeding in that exposed part, but it’s not as much work as weeding an entire bed continuously.

Removing sod is a lot of work and can be expensive if you can’t do it yourself.

But mowing down the grass and weeds is a good idea.

Water The Area

If it’s dry, it makes sense to water the area as water will begin a sort of composting underneath the other layers you’re adding.

Water will help the area heat up to break down the grasses and weeds after the next layers are added.

We started our garden site in the spring after heavy rains, so this was not necessary.

Cut a Clean Edge Around the Section (Optional)

Completely optional!

Use an edging tool to hack out the shape of the bed you’re creating.

We did this for all of our decorative flower beds, but did not do it with the vegetable beds. We did choose to create a path edged with stones though that presses up against the mulch, but again, this is up to you and what your aesthetics are.

Edging a flower bed that will be an island in the midst of grass can look fantastic and formal, the bare soil will be a striking contrast against the grass.

Two sage green raised metal beds sitting on multiple layers of overlapping brown cardboard.

Place the Weed Suppression Barrier Over the Area

Once the area is mowed down and watered — add your weed suppression layer.

We opt for natural choices and sheet mulching with cardboard for best results.

Cardboard is free and readily available.

I recommend you seek out big box stores like Costco and those that sell appliances and call ahead to get to the cardboard before they crush it or throw it away.

Your best bet is two lay down two overlapping layers of cardboard as you can see in the photo above of our garden site being built.

Three layers works too.

Yes, cardboard breaks down, but it takes a very long time to do some. About 4-6 months or even longer.

Just as good as cardboard — whole leaves.

Weed Suppression Options:

  • Cardboard
  • Whole leaves
  • Newspaper
  • Sheep fleece or wool carpet (carpet should be removed before mulching or planting)
  • Landscape Fabric (expensive, frequently plastic)
  • Black Plastic (microplastics, can you trust it not to leach chemicals?)

Watering the Cardboard/Newspaper

An optional step. Watering the cardboard keeps it firmly in place from the weight of the water.

We did not do this.

Add Soil & Compost (If Applicable)

Depending on what you’re doing, you may be adding a layer of organic materials like compost or leaf mould on top of the weed suppressing layer and underneath your mulch.

You would consider doing this if you’re preparing the soil underneath for direct planting and wanted a nutritious layer on top to aid in regenerating the soil underneath.

We are doing this in our permaculture orchards and food forest.

This was not necessary in our annual garden site where the only function of mulching was to kill grasses and perennial weeds.

And it is not strictly necessary in any case.

Close up of a green metal raised bed. It is empty but underneath it is hardware cloth and it is sitting on top of a thick bed of wood chips. The hardware cloth juts out a few inches around the outside of the raised bed.
My Vegega metal raised bed on top of wood chip mulch. This is from our garden build spring of 2023 which you can follow along with on Instagram.

Add Mulch Of Choice

How much mulch to add depends on the mulch.

You will add a thick layer of mulch. About 4-6 inches ideally if using something like wood chips or bark mulch as the the pieces are larger.

But how many inches of mulch will depend on what you’re using.

For fine mulch types, you will want slightly less, about 2-3 inches.

If the area being mulched is primarily used for foot traffic, like between raised beds, use as much as possible before it begins to pile up too high.

What is the best mulch?

Like countless others, we opted to use wood chips.

You can get free truckloads (we had 30 yards!) of wood chips delivered from arborists that need to get rid of the stuff.

Or you can buy the fancier colored wood chips from garden centres.

What other options do you have? I’ll give you a list below.

A market garden row of green lettuce growing out of the ground.

Add Plants & Other Structures

Add your new plants, your raised beds or straw bales, your decorative edges and borders etc.

I like to add extra mulch around plant stems.

Watch for any weeds and pull those that come up immediately.

So far we have had nothing come up weed-wise in the mulched areas we have done ourselves on this new property.

Refresh Mulch Periodically

Expect to lose an inch or so of organic mulch each year and replenish it accordingly.

Old mulch will break down, wood chips and bark being very slow.

We do this in the spring after the snows have melted and it’s time to tidy up the garden beds and land.

Best Mulch to Put Over Grass

The best type of mulch to use to suppress weed growth, divided into organic mulches and inorganic ones. I highly recommend sticking to natural materials. Each choice will have it’s own advantages and disadvantages, and if I were to pick the best option if would be wood chips or bark.

Organic Mulch 

Inorganic Mulches

  • Rubber
  • Plastic sheets
  • Gravel, pebbles, rocks
  • Reflective metallic mulch
  • Landscape fabric

Related

Advantage of Laying Mulch On Grass Over Sod Removal

There is honestly no point in removing sod from the entire area you will be mulching, nor is there any point in tilling the earth.

Your choice of weed suppression and mulch will smother and compost the grass and weeds and feed the soil underneath.

If you plan on planting a vegetable garden in-ground, you only really need to add 6-inches of compost to make that a reality, no tilling required. However, if you can’t add that much organic matter and have no plans to install raised beds, then tilling once might be a good option too.

A large fence with unmulched grass and planters.
Adding mulch here would greatly decrease the maintenance of mowing and weeding, and provide an attractive border.

For all the information you need on mulching in your garden, check out my guide Benefits Of Mulch In Your Garden {Ultimate Guide To Mulching} for all the best resources and knowledge.

Final Thoughts

How to lay mulch over grass is a simple process of a primary weed and grass suppression layer like cardboard, followed by a thick mulch layer like wood chips. This is a simple project and relatively cheap too as the best mulches are basically free for the taking or dirt cheap. Along with composting, mulching is an incredibly important activity in your garden.

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