Mulch Matters: Understanding Materials and Methods

On November 13, 2024November 13, 2024 By durhammastergardenersIn arborist wood chips, Durham NC, fall gardening, garden tasks, gardening, Gardening calendar, Gardening information, ground covers, inorganic mulching material, lasagne mulching, leaf mold for mulch, mulch, mulching and soil chemistry, mulching garden beds, mulching iwth paper, mulching leaves, mulching trees, mulching with arborist wood chips, mulching with cardboard, mulching with paper, organic mulching material, over mulching, plant fungi, plant pathogen, proper mulching techniques, regenerative agriculture, renewable gardening, sheet mulching, soil, soil coverage, soil health, soil microbes, tips for effective mulching, tips for proper mulching, Uncategorized

By Eric Wiebe, NC State Extension Master Gardener^SM volunteer of Durham County

(Image credit: Allie Mullin)

As the gardening season is winding down, it’s time to start thinking about your fall and winter tasks. Near the top of that list should be thinking about mulching your plantings. A tour of your yard will probably reveal thin or bare spots where last year’s mulch has either broken down or been washed or blown away (those darn leaf blowers!). You may also want to put a winter cover on areas where you had vegetables growing. Finally, you may also have new areas you are preparing as garden beds where mulch will need to go around the new plantings.

Why Mulch Matters

First, let’s review why you want to be mulching in the first place. The primary reason most people mulch is for a combination of weed suppression and moisture retention. However, there are other just as important reasons to mulch. If you are using organic materials, you have the important benefit of in-place composting and humus generation, improving the biodiversity of the ground ecosystem throughout the mulch and into the surrounding soil and plants. Depending on type and placement, mulch can also help with erosion control and compaction. In addition to absorbing and holding moisture from rainfall, it can also minimize water splash from the underlying soil onto plants–potentially limiting the spread of harmful soil-borne fungi, such as blight. Finally, there may be good aesthetic reasons to mulch to create sharp delineations in color and texture in the landscape.

Types of Mulching Materials

What kinds of materials can you mulch with? Broadly speaking, mulches are grouped into organic and non-organic types. Included in organic materials are natural products, primarily from trees, that have been processed but will readily decompose–this includes cardboard, newspaper, and other paper products.

Inorganic Mulch

The most common non-organic materials are landscape fabrics made from plastic–either sheet or woven–and various types of stone. These are often used together, as the landscape fabric can be placed under the stone to help suppress weeds and keep the stone from migrating into the soil. Plastic sheet, with or without perforations, is also used in fruit and vegetable production, often applied with specialized machinery. The rest of the blog post will focus on the more popular and beneficial organic mulches used by home gardeners.

Organic Mulch

While shredded hardwood comes to mind when thinking about mulch, other organic materials like leaves are great sources for mulching material. As they decompose, leaves improve soil health by providing nutrients and improving both water retention and percolation. (Left) Newly-raked leaves ready to be spread across the garden. (Right) Leaf mulch after a year of decomposing. (Image credit: Eric Wiebe)

Organic materials can be found from a variety of sources. The best and most convenient materials are those found right in your yard. This includes leaves, new or partially decomposed; grass clippings, compost, and plant and tree trimmings. There is the argument to be made that the best mulch sources are the most local, as they represent the local ecosystem and can best support the macro-/microbiome already in your yard.

(Left to right) Arborist chip drop ready to be spread and a close-up of this type of mulching material. (Image credit: Eric Wiebe)

If you don’t have enough organic sources of mulch within your own yard, consider arborist wood chips. These are the product of local tree services as they cut down and chip tree limbs and can be acquired for free through a national service, ChipDrop (https://getchipdrop.com/). This product is still relatively local, representing tree species from your area and, for most of the year, contains a mixture of bark, wood, and leaves.

Research has shown that wood chips perform well with regards to moisture retention, temperature moderation, and weed control. While you can buy shredded (often from grinding whole trees), bark, and sawdust mulches from garden centers, many of these products are imported from other areas, bagged in plastic, or dyed. All of these factors both increase your cost and reduce their sustainability. In contrast, the biochemical and physical diversity of arborist chips resists compaction and creates a more diverse habitat for insects and microorganisms. Over time, the bark, wood chips and leaf matter will decompose, adding nutrients to the soil.

Paper products like newspaper and cardboard have long been used for sheet mulching/lasagne gardening techniques. Here a homeowner is using cardboard shipping boxes stripped of labels and tape as a base layer to be covered by other natural mulching materials. (Image credit: Melinda Heigel)

There are many, many other types of organic mulches that can be used. Pine straw is popular in NC and can be very local if you have a lot of pine trees on your property. While compost can also be used as mulch, its cost typically prohibits its use over a large area. Finally, paper products in the form of cardboard, newspaper, and brown paper have long been used as a form of sheet mulching. Note that you typically have to cover these materials with a somewhat dense mulch (e.g., partially decomposed leaves) in order to hold it in place. While there has been some social media controversy over the use of cardboard, it is still generally believed to be a quality mulch material when applied properly. Note that you should carefully remove non-decomposable elements such as tape and staples, and avoid glossy, non-brown cardboard as they may contain unwanted inks and plastics. While grass clippings can be used as a mulch, it tends to decompose quickly, not drain well when wet or blow away when dry. They may also contain excessive fertilizer or herbicides. Instead, consider mulching it in place in the lawn.

Tips for Effective Mulching

There are best practices to consider when using any mulch, and some considerations for specific types of mulches. First, to the best of your ability, plan how much area you have to cover and what volume of mulch you need. As a rule of thumb, you will need 6 cubic yards of mulch to cover 1,000 sq ft at 2″ deep–you generally will want to keep your mulch 1-3″ thick. However, this thickness will be driven in part by the density of the mulch; how well it retains moisture and allows oxygen to pass through it. Lighter mulch material such as pine straw or newly raked up leaves can often be deeper, while wood chips should be around 2-3.” If mulch is piled too deep, is too fine, or retains too much water, air cannot penetrate the mulch layer and the mulch and underlying soil can be depleted of oxygen. Mulch decomposing in low oxygen (anaerobic) conditions will sour, or ferment, producing methanol and acetic acid, which can be toxic to plants.

(Left to right) A properly-mulched tree has a few inches of mulch that extend to the edge of the drip line (or area that mirrors the tree’s crown). The root flare is visible at the base of the tree, as mulch isn’t in direct contact with the trunk. By contrast, the tree on the right is an example of all-to-familiar over mulching. Known as “volcano mulching,” mounding mulch around the trunk is harmful to your tree, leading to its decline and possible death. (Image credit: Penn State Extension; Eric Wiebe)

For all plants and trees, make sure to apply mulch all the way out to the drip line as you want to provide weed suppression, moisture retention, and soil benefits to all of the roots of the plant. Trees are another case of the dangers of over or improper mulching. Mulch should not come in contact with the bark of the tree as it promotes the kind of dark, moist environments that allow harmful fungi to enter the tree through the bark. Think donuts rather than volcanoes when you mulch your trees.

Impact of Mulch on Soil Chemistry

Using pine straw mulch as an acidifier on blueberries. (Image credit: Eric Wiebe)

Mulches can influence soil chemistry. While most of the time, this is happening in a good way, you need to understand the properties of the mulch you are using. Pine straw and pine bark, for example, has a naturally low pH. While this may be a problem on some plants, you can use it to your advantage with acid-loving plants such as azaleas or blueberries. Organic mulches with a high carbon-to-nitrogen ratio, like sawdust, hardwood bark, or wheat straw, may induce a short-term nitrogen deficiency as it breaks down. If plants in the mulched area become chlorotic and growth slows, consider applying one to two pounds of nitrogen per 1,000 sq ft to compensate. Almost all mulches will have a very localized nitrogen deficiency at the boundary between the soil and mulch. However, this is good as it inhibits weed growth.

Many of the basics and a few of the nuances about mulching have been covered here. As with most aspects of gardening, you can, if you want, continue to go down the rabbit hole of the science of mulching. The resources below will get you started!

Resources and Additional Information

General guidelines on mulching trees and shrubs: https://extension.umd.edu/resource/mulching-trees-and-shrubs/

Mulching garden beds:

https://carteret.ces.ncsu.edu/2021/08/mulching-your-garden-beds

https://yardandgarden.extension.iastate.edu/how-to/using-mulch-garden

Benefits of using arborist wood chips: https://pubs.extension.wsu.edu/using-arborist-wood-chips-as-a-landscape-mulch-home-garden-series

Tips for mulching in the spring: https://ext.vt.edu/lawngarden/turfandgardentips/tips/Springtime_mulch.html

Comprehensive guide to mulching materials: https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource007193_Rep10385.pdf

Sheet mulching/lasagne gardening gardening with paper products: https://extension.oregonstate.edu/gardening/soil-compost/sheet-mulching-aka-lasagna-composting-builds-soil-saves-time

https://extensiongardener.ces.ncsu.edu/2020/01/sheet-mulching-2020-winter-piedmont-news/

Problems with over mulching: https://pender.ces.ncsu.edu/2020/10/can-too-much-mulch-killl-plants/

Article Short Link: https://wp.me/p2nIr1-5iR

Leave The Leaves: A Simple Way to Help Wildlife and Your Garden

On October 23, 2024October 23, 2024 By durhammastergardenersIn bees, beneficial insects, composting, dealing with fall leaves on lawn, Durham NC, fall gardening, garden design, gardening, Gardening information, gardening NC, insects, lawns, leaves, mulch, pollinator gardening, pollinators, soil, soil health, soil microbes, sustainability, sustainable gardening, sustanability, urban wildlife

By Marcia Kirinus, NC State Extension Master Gardener^SMvolunteer of Durham County

Did you know that the National Wildlife Federation has designated October as Leave the Leaves Month? This initiative encourages people to rethink traditional fall yard clean-up by leaving fallen leaves in place—or at least on your property—instead of bagging them up and sending them to the landfill

Traditional fall clean-up often involves raking or blowing leaves, bagging them, and setting them out on the curb. Then we head over to the big box store to buy mulch and fertilizer to replace what nature is already providing. This process is time consuming, resource draining, and unnecessary. Leaves are not trash. We are missing an opportunity.

Instead, let nature do the hard work — your garden will thank you. The thing that is most natural to do — the thing that happens in nature — is to let your leaves lie where they fall. If you have extra leaves, bag them and offer them to neighbors or local gardeners who can make good use of them.

Beyond convenience, there are significant benefits to leaving the leaves. First and foremost, they nourish the soil. As leaves decompose, they enrich the soil with nutrients, promoting healthier, richer soils. Consider them free mulch and fertilizer. Second, leaves insulate the soil, protecting it from temperature fluctuations. They also help retain moisture. Finally, leaves make incredibly important habitats for wildlife. Have you noticed a decline in lightning bugs? Most of their life cycle is spent under leaf debris. By keeping your leaves in place you can boost wildlife habitats, enrich your soil, and even help with global environmental challenges.

Left: Adult Firefly. Right: Larvae of Firefly . Most fireflies are habitat specialists. They rely on undisturbed leaf litter for one year or more to complete their lifecycles. These insects spend most of their lives as larvae preying on earthworms and other animals in the soil or leaf litter. If that habitat is disrupted during their youth, populations can be extinguished. (Image credit M. Bertone, NCSU Entomology.)

Last year’s oak leaves slowly decomposing with the help of small pinwheel mushrooms (Marasmius rotula). Image credit: Jean Epiphan

Soil Enrichment: The Cornerstone of Healthy Gardens

Soils rich in organic matter absorb and retain water better, turning a soggy lawn into a sponge-like garden bed. In as little as two years, you can turn those wet areas into walkable spaces. It’s not a miracle as building soils naturally is a slow process, but it’s a start and it’s free.

Healthy soil, enriched by decomposed leaves, supports deep-rooted plants, reduces watering needs, and improves plant resilience.

Wildlife Benefits: From Moths to Bumblebees

Leaves provide shelter for many species, including fireflies, butterflies, Moths and endangered bumblebees. Caterpillars overwinter in leaf litter, which also sustains backyard birds in spring. By leaving leaves on the ground, you’re creating essential habitats for these creatures, helping maintain biodiversity and supporting the larger food chain, from insects to birds. Caterpillars, which overwinter in the leaf litter, are a primary food source for 96% of backyard birds during the spring.

From Left to Right: Luna moth pupae, ( Actias luna ), are often difficult to see as they are a chestnut brown and overwinter in leaf litter. In the spring it will emerge as a soft green, 3 to 4.5 inch moth. All life stages provide food for predators. (Image credit: Donald W. Hall, UF) Leaf litter is the ideal Earthworm habitat. Earthworms provide beneficial castings which are building blocks to healthy soil. (Image credit: M. Bertone, NCSU) Woolly bear (Pyrrharctia isabella) construct shelters like this one made from pine needles to protect themselves from the winter elements. They also commonly use leaf litter and other yard debris. (Image credit: batwrangler, flickr. with permission)

Small Acts, Big Impact: Helping with Global Change

By making small changes in how we manage our yards, we can create big environmental benefits—both locally and globally. Leaving the leaves isn’t just about benefiting your yard—it’s about making a difference on a global scale. Encouraging wildlife and helping to maintain a balance in the food chain is one way you are helping. By skipping the blower and rake, you also reduce fossil fuel consumption, lowering your carbon footprint. Additionally, leaves that are sent to landfills contribute to methane emissions as they decompose without oxygen. Composting them in your yard helps reduce these emissions.

If you still want to move your leaves around the yard, consider using a rake instead of a blower. Rakes are quieter, healthier for you, and don’t rely on fossil fuels. They also give you more control, allowing you to gently move the leaves without disturbing the soil or nearby wildlife. My neighbor for 17 years told me that he can rake faster than he can blow his leaves. I was dubious. At the time, my clean-up tool was a blower. However, I hated the noise and smell so I took his words as a challenge. I pulled out the rake and never looked back. I can rake faster, and with a lighter touch. I can listen to the birds and I feel stronger, fitter for doing so.

I also reduced my turfgrass lawn significantly so I can leave the leaves in place. I converted it into valuable wildlife habitat by planting native ferns and flowers. Lawns require water, fertilizer, and herbicides, not to mention mowing, which creates noise and uses fossil fuels. And lawns are wildlife dead zones. However, I still need a place to play fetch with Moira, so a small patch of “meadow” remains. I say meadow because it is green – mostly clover.

Making the most of your leaves

Here are a few simple strategies to keep them working for you. You don’t have to leave all the leaves exactly where they fall.

On Lawns: A thick layer of leaves can suffocate your lawn. Instead, run a mower over the leaves to chop them into smaller pieces. A thin layer (1–2 inches) of shredded leaves can actually nourish the grass over the winter, breaking down over time to feed the soil.
Flower or Vegetable Beds: Spread whole leaves in flower beds or vegetable gardens. They act as mulch, suppressing weeds and adding organic matter as they decompose, improving soil structure and fertility. For most garden beds, a leaf layer of 3–5 inches deep is ideal. Avoid piling leaves directly on top of plants; instead, place them around the plants, covering any exposed soil. This will suppress weeds, preserve soil moisture, and return nutrients to the roots as the leaves decompose.
Composting: Leaves are perfect for composting—rich in carbon and ideal for building fertile soil. Consider adding them to your compost pile or creating a leaf mold. If the wind blows leaves into unwanted areas, let nature guide them into natural piles, and then redistribute the leaves to your garden beds or around trees.

From left to right: Mower cutting leaves into small pieces instead of removing them (Image credit: Pixaby);. Moving whole leaves to help create paths by suppressing weeds (Image credit: Justin Butts). Composting excessive leaves (Image credit: Christy Bredenkamp, NC Extension Director, Moore County).

Conclusion: A Small Change with a Big Impact

With just a few thoughtful changes, as gardeners and homeowners, we have the power to make a positive impact on the environment by simply rethinking how we take care of our little piece of earth outside of our back door. This October, join the movement and Leave the Leaves—because every leaf left behind makes a difference.