Grass clippings are one of the best money-saving resources any gardener will have, and it doesn’t even matter what state your lawn is in. Grass is a high nitrogen feeder, but it stores that nitrogen really well in its leaves.
Using grass clippings as mulch will feed your garden, reduce the need for watering, and help to improve your soil. Every time you fill up your garden bin, or take your grass clippings to the tip, you’re giving away the most valuable garden by-product you have.
There are dozens of council waste facilities, literally making money from your waste, and it’s something that us gardeners will actively buy back; compost.
Why Use Grass Clippings as Mulch?
The most common mulch in our gardens is part-rotted bark. It’s effective, it prevent weeds from developing, and it looks good. But it’s not cheap. Grass clippings cost literally nothing, add more nutrients to your soil, by breaking down faster, improving drainage, and opening up your soil structure in the process.
Grass clippings can be used fresh, dried, composted, or even straight back onto your lawn to reduce nutrient loss. But perhaps, before we get into the fine detail, it’s important to clarify the benefits of mulching in general.
What Does Mulching Do to Our Gardens?
Mulching is the act of covering soil. You can use anything from shells, pebbles and slate, to bark, compost or grass clippings. Its primary purpose is to prevent annual weeds from germination and perennial weeds from re-sprouting.
Plastic sheets will do the job, but only organic mulches actively improve your soil (in fact, stone, plastic, or artificial mulches actively harm your soil health through compaction).
Adding generous layers of organic mulch encourages good bacteria, worms, woodlice, beetles, nematodes, slugs, etc. to work goodness back down into the soil. The results are not just more nutrition in your garden, but also improved drainage, and improved moisture retention.
Through summer, a generous mulch will help to retain moisture through periods of drought. Through winter, it will keep frosts and icy temperatures away from the roots of tender plants.
The Science of Mulching with Grass Clippings
But what makes grass clippings such a good mulch? Well, there are three significant benefits of mulching with grass clippings; moisture control, added nutrients, and improved soil structure.
For me, as a dedicated bargain hunter, the fact that grass clippings do all that for free makes them an obvious choice.
How Grass Clippings Retain Moisture
Grass clippings can be used as a dry or fresh mulch, and in both cases they will stop moisture loss during the summer months. This is as simple as creating a barrier between the beating sun and your soil.
The thicker you mulch, the more effective that becomes.
How Grass Clippings Add Nutrients
Grass is a heavy nitrogen feeder, drawing nitrogen out of the soil, and generally leaving the soil beneath your lawn depleted, and in need of regular feeding.
By saving your grass clippings, you can move the nitrogen they take out of your lawn onto other beds, borders, and veggie plots, to add the most important nutrient for plant development – nitrogen.
While grass isn’t the most effective nitrogen fixer, it does hold onto about 25% of the nitrogen it removes from the soil and offers much richer fertilizer than many types of manure.
How Grass Clippings Improve Soil
As grass clippings break down, they heat up, creating steam and humidity in and around the pile of greenery. That steam, for the most part, drips back down into the soil, encouraging higher-than-average rates of soil activity, from worms and other tiny organisms.
Grass clippings offer tons of nutrients, which creates a banquet for the beneficial insects and bacteria too, so attracts them to the surface, where they pull down rotting leaves, and poop them out as healthy soil.
As they dig up and down, they churn through your existing soil (whether it is clay, sand, or loam), aerating it, and adding organic matter up to 1m below the surface.
The results are a combination of better drainage, higher nutrition, better moisture retention, and an easier space for roots to grow without compaction or competition, which is ideal for nearly every plant you can grow.
When to Use Grass Clippings as Mulch
You can use grass clippings as mulch all year round, but aim to apply them to each part of the garden just once in a year. Over-application can cause excess moisture retention, and soil life just can’t keep up.
Use fresh grass clippings if you want to warm up your garden beds through winter. As they break down, they add heat, nutrients, and moisture to the soil, getting it ready for planting in early spring.
For the rest of the year, your grass clippings will dry out faster in the sun’s heat, so won’t get up as much, or break down as quickly. This makes them a more effective moisture-retaining mulch for longer. This works with dried or fresh grass clippings in equal measure.
My only real advice about when not to use grass clippings as mulch, is if your grass has gone to seed. All you’ll be doing then is spreading grass seed around the garden.
How to Use Grass Clippings as Mulch
Dried grass clippings can be used as a mulch in a number of ways, whether they’re fresh, dried, composted, or dug in with a bit more preparation.
Here are two of the easiest ways, and a few more specific uses too.
Using Dried Grass Clippings as Mulch
Dried grass clippings will break down more slowly than fresh grass clippings, and don’t have quite as much nitrogen. They also won’t break down with heat. The main benefit of dried grass clippings is to provide cover for soil, particularly around moisture loving plants during dry weather.
Apply dried grass clippings in 2-3” layers, making sure to keep them away from the woody bases of trees and shrubs.
Using Fresh Grass Clippings as Mulch
Fresh grass clippings are more versatile, have more nutrients, and heat up as they break down. This encourages more soil activity, and better moisture retention (it also reduces the need for storage as it can be used straight from the lawnmower bag).
Around our borders, we use fresh grass clippings in 2” layers as and when we get it. Our lawn isn’t huge, so we can usually cover about 3m2 each time we cut it. Avoid regular light mulches, and go for occasional heavy mulches, even if it means mulching every two years rather than annually.
Other Ways to Use Grass Clippings in the Garden
If you like your garden to look really neat and tidy all year round, grass clipping mulches might not be for you. Even I will admit that it isn’t the neatest looking mulch in the world.
If that’s the case, there are still a few great ways to use your grass clippings as a garden feed.
Composting grass clippings
The obvious one is composting. All you need is fresh grass clippings, and an equal amount of dried straw, dried leaves, newspaper, or even cardboard. Grass, or green waste, represents nitrogen. Brown or dried waste represents carbon.
Carbon and nitrogen are the ingredients for any good compost, so make sure you have a good mix of dry and green waste (of which, grass is the most effective and most abundant in most gardens).
One of my favorite ways to use grass clippings is trenching. It doesn’t use much, but it’s a really effective way to give annual climbing plants a boost, and works particularly well with beans and peas.
Dig a trench, about a foot deep, where you plan to plant your beans and fill half of it with grass clippings. Cover the trench back over with a slight mound (this will flatten itself out over the year), and then sow beans, peas, or annual climbers, directly into the soil above the trench.
The heat and nitrogen in the soil give such a boost, right through the season, and will definitely be a part of your annual garden routine.
And finally, the easiest way in the world to use your grass clippings is to take the mower bag off your lawn mower and cut it regularly.
Fine grass clippings can be left on your lawn to break down, putting used nitrogen back into the soil, and recirculating it to your lawn to use all over again.
Possible Problems with Using Grass Clippings as Mulch
Pests & Diseases
Like anything, grass clippings aren’t perfect. They can offer a safe breeding ground for bacterial and fungal problems, and if they are touching the trunks of young trees or shrubs as a mulch, can cause excess humidity and rot as a result.
Mealybugs and other pest species enjoy moist surfaces for eggs and larvae to thrive, and grass clippings offer an ideal habitat. However, other pests, like spider mites, need dry conditions, so fresh grass clippings make it nearly impossible for those pests to breed.
It’s very much about weighing pros and cons, but if paired with good garden maintenance, they are a safe, cheap, and effective mulch for any garden.
If you mulch with grass clippings while your grass has seed heads or flowers, then you risk spreading grass seed into your borders, which can sprout, and grow into clumps of grass where you don’t want them.
Insignificant flowers on many types of grass are hard to spot, but on most they look like short wheat or barley stems.
Frequently Asked Questinos about Using Grass Clippings as Mulch
How thick should a grass clipping mulch be?
Grass clipping mulch should be applied in 2-3” layers. Thinner layers don’t provide the nutrients or moisture retention necessary, and thicker layers can fail to stay aerated.
How do you compost grass clippings?
Compost grass clippings in layers, or turn your compost regularly. Low maintenance compost takes longer, but by adding a layer of grass clippings, a layer of vegetable or garden waste, and a layer of straw (or dried leaves, or shredded paper) and repeating that process, you will have beautiful compost in around twelve months.
How long does it take grass clippings to decompose?
Grass clippings that are spread thinly around your lawn will decompose completely within a few weeks, and won’t be visible for more than a few days. If you're cutting long grass, remove the clippings as they will break down more slowly and can block light to new growth.
Do grass clippings make soil acidic?
Grass clippings release ammonia as they decompose, so do acidify your soil slightly. Over-application on very poor draining soils can increase acidity to around 8.0, but a single annual mulch will support healthy pH levels.
Wrapping Up Our Guide to Using Grass Clippings as Mulch
I hope, if nothing else, that I’ve convinced you to stop throwing your grass away. You’re offering a gold mine of garden nutrients to your council that you could be making use of yourself.
Whether you’re mulching, trenching, or using a mulching lawn mower to recycle your grass clippings, they are just too good to waste. There is nothing more satisfying than saving money in the pursuit of good gardening, and using grass clippings as mulch is a tried and tested way to do both.