A well-designed landscape not only adds aesthetic appeal to your outdoor spaces but also offers many ecological benefits. One key element that can significantly contribute to the overall health of your garden is landscape mulch. However, I consider mulch to be a tool rather than a design feature. In this blog post, we will explore the benefits of landscape mulch, discussing its various types and the advantages it offers for your plants and garden.
The primary reason we have historically used mulch in the garden is for weed suppression. Landscape mulch serves as a moderately effective weed suppressor when applied a minimum of 4" thick, but also blocks a plant's ability to reproduce by seed, stolons, etc. Self-reproduction is no longer considered a bad thing in a garden, as it is useful to allow plants to reproduce themselves naturally to fill in the space with... GREEN MULCH! More on that below.
Mulching does help conserve soil moisture by reducing evaporation, especially during hot and dry periods. However, if you are using "tanbark" -- the traditionally used mulch here in the Mid-Atlantic -- it forms a dense crust that is impenetrable to rainwater. Blocking rainwater from reaching your plants and shedding it off into the lawn or paved surface is not good for them at all. If you have this type of mulch in your landscape, rake it frequently to break up that crust.
Inorganic mulches such as gravel or river rock require landscape fabric to be installed underneath. This prevents the stone from sinking down into the soil. Landscape fabric should never be used in a planted bed as it restricts the flow of water and insect movement in and out of the soil, creating a very unhealthy soil condition. Both landscape fabric and heavy stone mulch also restrict a plant's ability to grow and expand. Stone mulch is sometimes used as a design element, installed in large swaths to break up a mulched bed and left unplanted. This is essentially an inexpensive hardscape and creates an area that is unusable to both humans and wildlife. I don't get it. Using stone mulch makes sense in areas that are very dry and/or fire-prone, but here in the Mid-Atlantic, stone mulched areas will quickly become weed factories. Hand weeding stone mulch is very hard on the fingers or requires herbicides to manage.
Organic mulches, in contrast, break down over time, contributing to soil health and fertility. Mulch enriches the soil by adding organic matter, which improves its structure, moisture-holding capacity, and nutrient content. Microorganisms and beneficial insects thrive in mulched areas, promoting a healthy soil ecosystem.
Let's discuss the organic mulch options available.
Bark Mulch: Bark mulch, derived from the outer layer of trees, is one of the most popular organic mulch options. It comes in various forms, including shredded bark, wood chips, and nuggets. Bark mulch offers excellent moisture retention and temperature regulation. It breaks down slowly, contributing to long-term soil health and stability.
Wood Chips: Wood chips, also called arborist chips, are a byproduct of tree pruning or tree removal. They provide effective weed control and moisture retention while adding a natural look to your garden. Wood chips decompose gradually, releasing nutrients into the soil over time. They are ideal for woodland or shade gardens. Don't let anyone tell you fresh wood chips steel nitrogen from the soil. That's a gardening myth: Maddening mulch myths – The Garden Professors™
Straw: Straw mulch is an affordable and readily available option for organic gardening. It is commonly used in freshly seeded areas. Straw helps conserve soil moisture while seedlings grow, adding organic matter to the soil as it quickly decomposes. Only use straw when you don't need a mulch cover for more than a few weeks.
Pine Needles: Pine needles, also known as pine straw, offer unique characteristics as mulch. They are acidic in nature, making them an excellent choice for acid-loving plants like azaleas, rhododendrons, and blueberries. Pine needles provide good moisture retention and insulation against temperature extremes. They look most natural in areas already populated with pine trees.
Leaves: Leaves are a free and abundant mulch source in the fall. They provide excellent weed control, retain moisture, and promote a very healthy soil ecosystem. Leaves break down quickly (quicker if you shred them with your mower), adding nutrients back into the soil. Keep those fall leaves, they are gardener's gold!
Make it a combo: A 50/50 mix of wood chips and natural leaf compost is the ideal mulch with the exception of...
Green Mulch: The absolute best mulch you can install is green mulch. And by that, I mean PLANTS! The best option for soil and plant health, as well as wildlife value, is to plant densely and completely cover your garden space with plants. This means planting every 12" with perennials and groundcovers, including groundcover plants under your shrubs and trees. Upon installation, use about 2" of wood chips or the 50/50 combo as mulch around your new plants. The plants will fill in over the next 2-3 years and you will never replace mulch in that area ever again. The plants will shade the ground, preventing new weeds from growing, and replacing "weed" seeds with "plants you want" seeds. Yes, it's a greater upfront cost, but much less work/cost in the long run, more sustainable, and much healthier for the soil, wildlife, and humans too. Think about how plants grow in nature. Nothing grows as an isolated plant in a mass of mulch, but in a tightly packed community.
Organic mulches offer an array of benefits to your garden. The choices are abundant. Maybe it's time to rethink the aesthetic appeal of a sea of black mulch and ignore the marketing on the bags at the big box stores. Enjoy the natural goodness and sustainable advantages that organic and green mulches provide. Happy gardening!
tl;dr
Rethink mulch as a tool to help establish new plants rather than a design feature of your landscape.
Organic mulches should be used only upon installation of a new bed around young plants. Natural wood chips, leaf compost or a 50/50 combo is best.
Inorganic or chemically treated mulches create an unhealthy situation for soil and plants.
Green mulching your beds is the healthiest, most sustainable option.