I live in a neighborhood of neatniks. Walking down my street, I always admire the beautifully tidy garden beds, replete with ornamental gravel or earthy bark, healthy plants springing forth and flourishing year after year.
The Value of Mulching
Everyone loves a weed-free garden, and a layer of mulch works by preventing the weed seeds from germinating, blocking their light, and smothering them if they do manage to sprout.
Depending on the material you choose to use, there are many benefits over and above just preventing weeds from taking hold.
Soil Moisture and Erosion
Texas A&M reports that mulching, a long established horticultural practice, is beneficial because it prevents erosion, especially on sloping beds or furrowed rows. In especially arid or rainy climates, erosion is a common issue.
supplemental irrigation, and cutting down on high water bills.
Additionally, having fewer weeds competing for moisture will mean more of it is available for your crops.
Another important aspect of mulching is the effect on soil temperature.
Extreme soil temperatures can put unnecessary stress on plants, making them weak and vulnerable to pests and disease. Mulching helps to regulate soil temperature, keeping it constant, and less prone to fluctuation.
According to a study by Edyta Kosterna, published by the Polish Society for Horticulture in 2014, placing a layer of straw mulch over the soil around tomato plants showed a significant reduction of daily temperature fluctuations of the soil, and concluded that mulching increased the total yield of fruits.
Enrich and Nourish
Depending on what you use, mulch can help to regulate soil pH, add nutrients, and increase the fertility of your soil over time.
By using natural materials that gradually decompose, it can help to aerate the soil and prevent it from becoming compacted, improving texture.
Broadly speaking, materials used for mulching fall into two categories: organic and inorganic.
Organic mulches are natural materials that will gradually decompose and improve the condition of the soil.
Inorganic materials, used primarily for weed blocking, are non-biodegradable and can look very decorative in borders and containers, improving the appearance of your garden.
The Natural Resources Conservation Service (NRCS, a part of the USDA) offers some suggestions.
Bark can create a pleasing look in your established borders and under trees. It comes in a variety of different sizes and colors, from coarse-cut pine bark nuggets to finely shredded hardwood.
The coarser the cut, the longer it will take to decay, so you won’t need to top it up too often. It keeps the weeds in check, and prevents water evaporation and runoff.
Shredded or finely chopped bark will break down more quickly, adding organic matter to the soil. While the US Department of Forestry says that it has no specific value as a fertilizer, bark is a very good soil conditioner, conserving moisture and reducing erosion.
Some gardeners are concerned about the use of bark – and wood chips – on the basis that they deplete nitrogen from the soil as they decompose. Wood-based mulches have a high carbon-to-nitrogen ratio, and the fear is that the microbes responsible for breaking it down will tie up nitrogen in the soil.
Both the US Department of Forestry and Texas A&M are of a different opinion.
The only time that nitrogen depletion might be an issue is if the material were to be dug in and incorporated into the soil, before it has time to decompose. By placing the mulch on top of the soil, nitrogen depletion is not an issue.
You can also find bark that’s been dyed to a uniform color.
According to Ron Kujawski at the Center for Agriculture, Food, and the Environment at the University of Massachusetts Amherst, these dyes are not considered toxic. But my own preference would be to use avoid using dyed materials in areas where I’m growing edible crops, or to avoid them altogether.
Bark will usually need to be reapplied every 2-3 years, depending on the size of the chips.
This is my favorite option. Composted organic material is the best thing you can use to mulch your soil. The organic matter has already broken down, and it will release nutrients into the soil readily.
Just make sure the compost is well rotted, so it doesn’t contain viable weed seeds. Dig from the bottom of your compost pile, or buy it in bags from a garden center.
Ah, summer, filled with the smell of freshly mowed grass. But can you mulch with grass clippings?
Photo by Clare Groom.
Thick layers have a tendency to become compacted and matted, creating a slimy mess in the garden. To avoid this, apply a thin layer of dry lawn clippings and add to it every few weeks.
If you’ve got a very weedy lawn, then it’s better to compost the clippings first, to prevent introducing new weed seeds into your borders that are ready to sprout.
Leaves and Leaf Mold
Fresh or shredded leaves make a good mulching material for perennial beds and vegetable gardens. Not as decorative or neat as bark, they’ll break down quite quickly and add nutrients to the soil.
The forest floor demonstrates how nature provides its own all-in-one mulch and compost in the form of fall leaves, which turn into leaf mold.
In the home garden, leaf mold is a type of chopped, partially composted leaf matter. It provides an excellent soil amendment.
You can make it easily at home, by raking fall leaves into a pile after running the lawnmower over them to shred them, then covering with a tarp to keep them moist, and leaving them in place for a year to decompose.
Underneath, you’ll find a rich, brown leafy material perfect for mulching your garden.
snails and slugs. These like to hide in the cool dark of leaf mulch during the day, coming out at night to nibble on your tomatoes and lettuce. Keep in mind: they may like to shelter in other types of mulch as well.
We’ve all got newspaper lying around, haven’t we? Let’s put it to good use in the garden!
Layers of newspaper can be used as a natural base underneath bark or decorative gravel. It provides an additional layer of weed control, and newsprint eventually breaks down, adding organic matter to the soil.
Shredded, it can be used on its own. But note that it will decompose quite quickly and isn’t particularly decorative, as it tends to get clumpy when wet.
You can use newspaper in existing beds as well as on bare soil or fallow garden beds. It’s often used as part of the practice known as lasagna gardening, to add a carbon layer.
Pine needles are an excellent mulch for blueberries, rhododendrons, or other ericaceous plants that thrive in acidic conditions.
If you have a local source of sawdust available, it’s best to partially compost it before using it as mulch in the garden. In the early stages of decomposition it can potentially contribute to soil acidity, as it has a very high carbon-to-nitrogen ratio.
Mixing with some well-rotted manure will create a nutrient rich, decorative mulch. Be careful about laying it on too thick, as it tends to get hard and form a crust on the surface, preventing moisture from reaching the soil.
Sawdust will decompose faster than bark or wood chips, and you’ll either need to top it up or replace it at the end of the season.
Only use sawdust gleaned from untreated timber, as treated wood can contain toxic substances such as copper chrome arsenate (CCA).
Stones and Decorative Gravel
Landscaping with rocks can certainly add curb appeal. From large river rocks and pretty pebbles, to shingles and stone chips, they can provide a practical and appealing finish.
As they are not biodegradable (not quickly, at least), they won’t offer any of the soil improvement advantages of organic, biodegradable materials. But they will suppress weeds and conserve moisture.
They also won’t need to be replaced or replenished; rocks can last a lifetime.
I like to use stones in narrow borders running along a fence line or containers on the patio, as it can get expensive – and heavy – to use them in large areas.
Adding a layer of newspaper underneath is a good idea, as some persistent weeds may start sprouting in between the rocks or stones.
Straw and Hay
Commonly used on or around vegetable crops, hay and straw are lightweight materials, often applied for overwintering as they don’t damage the plants.
Wood chip mulch can either be made from recycled wood and off-cuts from timber yards, or from a felled tree by putting it through a shredding machine.
A cheap – often free – way of acquiring some wood chips is to contact your local arborist. Expert tree pruners often have too much excess, and are happy to give it away.
University of Vermont’s Department of Plant and Soil Science, arborist wood chip mulch is one of the best types available for retaining moisture, maintaining even soil temperatures, and suppressing weeds. It’s also one of the best in terms of environmental sustainability.
This is because it contains bark, wood, leaves from the tree, and as each of these breaks down, they provide nutrients to the soil.
Using wood chips can attract beneficial mycorrhizal fungi, decomposing the organic matter into a fungal-dominant soil. It’s ideal for use in orchards, around trees, and for woody shrubs that need a fungal soil to thrive.
Easy to use, wood chips are an effective weed blocker and, like bark, they provide a natural, tidy appearance.
The Process of Mulching
The best times to apply mulch are in spring – or early summer – and fall, though this will depend on where you live.
According to the Royal Horticultural Society, you want to avoid applying mulch in summer if the soil has already dried out, or too early in the spring if the soil is frozen.
Winter mulching to protect cold tolerant plants is done in mid- to late fall.
conduct a soil test to determine the pH of your soil, and select your material accordingly.
For example, you don’t want to add acidic material, such as pine needles, to soil that is already acidic, unless you are growing rhododendrons, blueberries, or some other acid-loving plant.
Take the time to weed the area thoroughly – watch for runners of grass roots, and get rid of them. Cultivate the soil and apply any amendments, such as compost, if needed.
If you are mulching around existing plantings, be careful not to disturb roots, or damage plants. Now is a good time to tidy up the edges of your borders, for a neat and orderly appearance.
writing your garden journal, instead of pulling up weeds.
If you want to find out more about how to improve your soil, visit these guides next:
- Using Borage as a Cover Crop and for Green Manure
- The Benefits of Using Soil Inoculants and Microbes in the Garden
- Understanding the Soil in Your Own Backyard
Clare Groom’s gardening experience ranges from tropical East Africa – where common crop pests included elephants as well as aphids – to growing a cottage garden in the Cotswolds, England. A writer from London, Clare retired from the high-octane world of professional financial futures trading to live a peaceful life in the Bay of Plenty, New Zealand – and to pursue her love of words. When she’s not writing and editing, she’s chasing possums off her zucchini and renovating an old house in a small town – slowly, and not very surely.