Mulch is simply something that is put on top of soil. It can be organic, like natural wood, or mulch can be inorganic, like rubber pieces. (Not surprisingly, I strongly recommend using organic mulch and staying away from inorganic mulch).
Using a good mulch is one of the best things that we, as gardeners, can do for our gardens. I rely heavily on mulch to keep my garden looking neat and tidy, and my plants healthy and happy. Indeed, mulch doesn’t just look great, it’s part of nature’s way of protecting the garden soil and has a number of important benefits.
Overall, by using mulch I make gardening easier for myself throughout the growing season. There is less weeding and watering, and more time enjoying beautiful blooms. More technically, mulch conserves soil moisture, suppresses weed growth, regulates soil temperature, and improves soil health all while helping your garden beds and trees look great. I’ll start with how great mulch looks on a landscape.
1. Mulch is beautiful on a garden.
I first started using mulch because it looks great. I like that it gives my garden a more professional, finished look, and it makes it easier to keep the beds clean and organized.
I use a few different types of mulch on my gardens but I only use organic mulches. When I first started gardening, I used black dyed mulch because the bags were cheap, and the black looked great. However, as I started to read more, I learned that dyed mulches aren’t great for a garden and the black color helped trap heat that isn’t always good for plants, especially during our hot Northern VA summer months.
As a result, I stopped using black dyed mulch, or any dyed mulch for that matter. While I missed the brown and black color options of a dyed mulch at first, I am now able to get color contrasts but with better, more natural mulch products. I like that organic, natural mulches create a win-win for beauty and soil health.
Because mulch comes in so many colors and sizes, I think it’s a fun way to show my style and vision as gardener. I especially like playing with the size of the mulch for my gardens. For paths or walkways, I use a coarser product, like a single or double shredded mulch. This is lighter in color and larger in particle size. The larger size helps prevent compaction when walking on the path as well as creates a nice contrast to the garden beds, where I use a different color and/or smaller size.
For garden beds, I use a double or triple shredded mulch, or a leaf mulch. Because the sizes of the pieces of wood are relatively smaller, they create a smoother surface and I think this gives the garden beds a cleaner look.
For my native plant beds at our composting facility in Manassas, VA, I use a double shredded, natural mulch—this is the largest particle size that I use on plant beds. Compared to the other options, I think it looks slightly rougher and more like what I see walking through the woods.
For my veggie garden, I like our triple shredded mulch because it breaks down faster to give the nutrients back into the soil and has a sharper contrast in mulch size versus what I put down in the pathways of the vegetable garden. Straw or a leaf mulch are also great options!
I use a leaf mulch at my house because I want an especially neat and tidy look for these garden beds. Because it is just ground up (and processed) leaves, it lays very flat across the top of my soil and creates a sharper line against my grass or the side of my house.
Overall, mulch is beautiful. While I often geek out about the soil health benefits of a natural mulch (that’s next!), I garden because I love having a beautiful landscape around me, and mulch is a critical part of the aesthetics.
2. Mulch holds moisture in the soil.
Mulch helps with moisture retention in the soil, reducing the need for frequent watering. This saves me time and money. (Mulch for the win!)
It can be hard to keep plants hydrated, especially in our DMV summers. Watering plants every day is time-consuming and can quickly add up on a water bill. A layer of mulch acts like a barrier over the soil to reduce evaporation from the soil surface. This keeps more water in the soil for longer, so that plant roots can grab a drink when thirsty.
Native plant gardens are the best at adapting to any unique weather patterns in our region. In my native garden at our composting facility in Manassas, VA, I only need to make sure that the plants get two inches of water each week during the growing season. If there’s a good rain during the week, this means that I might not need to water at all.
The US Department of Agriculture notes that a layer of mulch only allows 10% of a rain’s water to evaporate, compared to 80% rainwater evaporation for soils without mulch.
In the studies that I have seen referenced, mulch can increase the soil moisture content by up to 50%, and reduce water usage by up to 40%. (I haven’t accessed these studies to double check the details.)
Forster and Gibson found that mulch can increase soil moisture content by (up to) 50%, and reduce water usage by (up to) 40%. This is because the layer of mulch significantly reduced evaporation from the soil surface, conserving water and increasing soil moisture content (published in "Horticultural Science" in 2000).
Brandt, Ashworth, and Mortensen showed that using mulch can reduce the frequency of irrigation by up to 50% (published in "HortTechnology" in 2006).
McGiffen Jr, Rhodes, and Cushman found that mulch can increase soil moisture by up to 40% ("Mulch and soil moisture in container-grown woody ornamentals," published in "HortScience" in 1999).
Overall, using mulch saves me time and money by reducing how much and how frequently I have to water. Not having to stand outside in the hot summer heat? Priceless. (I actually do my watering early in the morning to beat the heat—this is better for my garden too--but I’m equally happy not to have to fight the mosquitos.)
3. Mulch reduces weeds.
A layer of mulch helps limit the growth of weeds. By using 2-4 inches of much on my garden, I don’t have to weed as frequently and the weeding that I do goes much faster.
Nature wants its soil to be covered and weeds will find their way into the bare spots of a garden quickly to try and cover it. These weeds can compete with plants for nutrients and water. One New York Times article noted that weeds could steal as much as 25% of the moisture that would otherwise go to plants!
Because mulch is a covering for the soil, it makes it much harder for weeds to germinate and grow. If a weed seed lands on top of the mulch, it will have a hard time growing its roots down to the soil to get nutrients to grow. If a weed seed works its way down to the soil surface so that it’s roots can grow, it will have a hard time getting enough sunlight to grow.
Studies have even shown that a layer of mulch can reduce weed populations by up to 90%. These are the studies that I’ve seen referenced (but I haven’t accessed them):
Brandt, Ashworth, and Mortensen showed that mulch can reduce weed populations by up to 90%. Their study found that the use of mulch as a weed control method was more effective than manual weeding or the use of herbicides (published in the journal "HortTechnology" in 2006).
McGiffen Jr, Rhodes, and Cushman found that a mulch layer can reduce weed populations by up to 90% in container-grown woody ornamentals. They also found mulch was more effective than herbicides (published in the journal "HortScience" in 1999.)
Forster and Gibson found that mulch’s weed suppression can be as high as 99% (published in the journal "Horticultural Science" in 2000).
By the time our summer heat rolls around, I’m glad that I put down a layer of mulch. At home, I can do weeding easily enough in the morning. At work in Prince William County, however, I weed during the workday. On these days, I’m thankful that I took extra time in the spring to get my mulch down.
4. Mulch helps keep soil temperature reasonable.
Mulch also helps regulate soil temperature, keeping the soil cooler in the summer and warmer in the winter. It can even help protect plant roots from frost damage during the winter.
Studies have shown that mulch can reduce soil temperature fluctuations by up to 20%. Here are the references that I’ve come across (but I haven’t accessed) them:
One study found that mulch can reduce soil surface temperatures by up to 15 degrees Celsius, which can be beneficial for sensitive plant species (published in the Journal of Environmental Horticulture in 2002). Zeglen and Mortensen showed that mulch moderates the daily and seasonal temperature variations of the soil surface and can reduce the soil temperature by up to 10 degree Celsius during the hot summer days (published in the International Journal of Biometeorology in 2001, "Mulch and soil temperature in an urban residential landscape").
5. Soil health
Organic mulch improves the overall health of the soil, helping plants grow better and healthier.
Organic mulches are made from natural materials, like wood chips or leaves. As this mulch breaks down over time, it adds organic matter to the soil, and this helps improve soil structure, increases water-holding capacity, and encourages the growth of beneficial microorganisms. This means better plant growth and health.
This is one of the biggest reasons that I’m not a fan of using inorganic mulches. While the idea of it not breaking down over time is appealing, it’s not natural. It doesn’t replenish my soil like an organic mulch does. If anything, there is a risk that small bits of an inorganic mulch breaks away and causes harm to local wildlife and/or waterways. I also think there are better uses for those materials (e.g. old rubber can be used to make shoes) and prefer to support its recycling into those areas.
Mulch can also help to prevent soil erosion, which can be a major problem in areas with heavy rainfall or steep slopes. I wrote about this quickly in an earlier blog post. In this case, it’s best to use a mulch that has different sized pieces, so I’d recommend a double-shredded mulch (and not our leaf mulch or triple shredded mulch for this use). The double mulch has a better variety of mulch piece sizes that helps hold the soil in place.
That’s it! We’ve covered five great reasons to use mulch. Indeed, I think adding an organic mulch to your garden is one of the best things that you can do for your landscape. If you’re ready to buy a mulch, I’ve written about my preferred types of mulch as well as how to buy a good bulk mulch.
You may notice that I didn’t mention using compost as a mulch in this article. In general, most composts, especially the ones that you'd want to buy, are too fine of a texture to carry all of the benefits of a mulch. I like following this as a rule of thumb: if a garden bed needs compost, it’s best to spread up to an inch and then put mulch over it. (This is a best practice for getting a garden ready for spring.)
Mulch gives your garden a professional, beautiful look good, makes plants healthy and happy, and can save you time and money. More broadly, giving the natural wood from Prince William County a place back on our local soil also helps the environment. This helps you, your garden, and our local environment Grow Good together.
Freestate Farms makes premium landscaping products—compost, topsoil, and mulch—by recycling food and yard waste in Manassas, VA. Our composts, topsoil, and mulches are specially designed to increase the health and productivity of local soils, and with our focus on sustainable practices, this lets the environment and your garden grow good, together. We sell bulk compost, bagged compost, bulk natural mulches, bulk dyed mulches, bagged dyed mulches, and bulk topsoil.