Mulching is a crucial garden practice that provides numerous benefits like moisture retention weed suppression, and insulation for plant roots. Mulch is typically made of organic materials such as bark, wood chips leaves, or compost and applied in a 2-3 inch layer over the topsoil. But some gardeners wonder, can mulch be mixed right into the soil instead?
There are differing opinions on incorporating mulch into the soil profile Some claim mixing it lightly can improve texture and nutrients Others argue it may cause issues with decomposition and nitrogen levels. In this detailed guide, we’ll examine the potential pros and cons of mixing mulch with soil to help you make an informed decision for your garden.
What is Mulch and How Does it Help Plants?
Before diving into the debate over mixing mulch into soil, let’s review the basics of mulching and its benefits:
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Mulch is a protective layer of organic or inorganic material spread atop the soil. Common organic mulches are bark, wood chips, straw, leaves, compost, or grass clippings. Inorganic options include stones, gravel, or landscape fabric.
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When applied correctly, mulch provides numerous advantages:
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Conserves soil moisture and reduces evaporation.
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Moderates soil temperature and prevents extreme flux.
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Suppresses weed growth and seed germination.
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Reduces soil erosion and compaction.
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Adds organic matter as it breaks down over time.
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Provides aesthetic appeal and landscape design element.
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Recommended mulch depth is generally 2-4 inches. Too little mulch is ineffective, while too much can be detrimental.
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Proper mulching is key to plant health. It mimics nature’s mix of organic matter and protects plant roots.
The Potential Pros of Mixing Mulch Into Soil
Here are some possible benefits touted by proponents of mixing mulch into the soil:
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Improves soil structure – Shredded woody mulch blended into heavy clay or compacted soil can improve drainage and aeration. The organic material creates spaces for better air and water flow.
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Adds organic content – Mixed into the top layer, mulch introduces additional organic matter to feed soil organisms and provide nutrients as it slowly decomposes.
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Increases moisture retention – The mulch particles integrated into the soil help it better absorb and retain water, reducing drought stress for plants.
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Warms up soil – Mulch mixed into the ground can absorb more heat than bare soil, which aids seed germination and root growth.
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Suppresses weeds – Incorporated mulch forms a barrier to block light and physically hinder weed growth.
For heavy, dense, or nutrient-poor soil, there may be advantages to lightly blending mulch into the top few inches to modify the soil structure and fertility. It brings conditions closer to nature’s mix of organic and mineral elements.
The Potential Problems With Mixing Mulch Into Soil
However, experts also cite some valid concerns regarding directly mixing mulch into garden soil:
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Can deplete nitrogen – Uncomposted mulch decomposing in soil can temporarily bind surrounding nitrogen that plants need for growth and development.
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May harbor pests – Burying fresh, woody mulch can create an environment for insects, diseases, or rodents to take hold and damage crops.
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Promotes uneven decay – Mulch breaks down anaerobically and incompletely when mixed into the soil profile, often leaving intact wood pieces for years.
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Causes muddy soil – Excess moisture retention from buried mulch leads to thick, compacted mud when walked on.
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Makes planting difficult – Chopped mulch integrated into the soil obstructs digging, weeding, transplanting, and other gardening tasks.
By altering soil biology and chemistry, mulch rotting within the soil can negatively influence plant productivity and health.
Best Practices for Using Mulch in Your Garden Beds
Most horticulture experts agree that applying mulch as a surface layer rather than mixing it with soil is best. Here are some recommended guidelines:
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Apply mulch as a 2-4 inch top dressing around plants, maintaining space between stems and trunks. This gives all the usual benefits.
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To improve soil properties, mix in fully composted materials like compost, manure, peat moss, or leaf mold. These incorporate safely.
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If using woody mulch in soil, only integrate thin layers, about 1 inch deep, of very well-rotted mulch to prevent decomposition issues.
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For heavy clay soil, try layering mulch, compost, and aeration amendments on the surface rather than blending them in.
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Use mulch for protection on top and compost to enrich the soil profile with stable organic matter and nutrients.
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Routinely test amended soil structure and nutrients and adjust applications accordingly to optimize growth.
The Bottom Line – Use a Light Hand When Mixing
Overall, most gardening experts recommend a conservative approach when incorporating mulch into beds to avoid over-amendment:
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Mix in thin, 1 inch or less layers at a time
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Use well-rotted, composted mulch rather than fresh materials
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Only mix into the top couple inches of soil
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Wait and retest soil before adding more
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Focus mulch application on the surface
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Think low and slow when integrating mulch into soil.
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A general rule is 1 part mulch to 10 parts soil.
Spreading mulch thickly atop the beds is better for plants than burying large quantities in the soil profile. Test regularly and adjust applications as needed. With a careful, balanced approach, you can enhance garden soil health without causing harm.
The Consensus – Surface Mulching Is Ideal
While partially blending mulch into soil may help modify and enrich it in small amounts, most experts recommend surface mulching as the best practice.
The problems that can arise from excessive buried mulch – nitrogen depletion, soil matting, uneven decay, moisture overload, and more – tend to outweigh potential benefits.
By supplying ample organic mulch atop the soil and adding fully composted materials into the ground, you get the ideal combination of surface protection and subsurface nourishment.
So focus your mulch application above ground and go low and slow if integrating limited amounts into soil. Test frequently, observe plant response, and adjust your approach until you find the optimal balance. With some trial and error, you can create healthy, living soil and happy plants.
Build smart soils using mulch, composted organic matter and reducing tillage
Learn steps for smart soil building right in your backyard or vegetable garden.
Photo credit: Normanack, Flikr.com
Home gardeners can build smart soils year round, but with the start of gardening season, now is a perfect time to plan and implement techniques that will create healthy soils for your vegetable garden. Sustainable practices include use of organic mulches, composted material and reducing tillage. Home gardeners can also look for more local sources of mulch and composted material.
Organic mulches can be grass clippings, compost, mulched leaves, wood chips, shredded bark, marsh hay or straw. All organic types of mulch break down over time and add nutrients back to the soil. Be cautious with the use of chips or bark; you may want to use it between your rows or areas of vegetable plantings rather than against the base of plants. Use chips or bark that isn’t freshly chipped and place it on top of soil rather than mixing it into the soil.
Where can gardeners find mulches? Look first within your own backyard. Michigan State University Extension does advocate that you return your glass clippings and mulched leaves back to your lawn, but if you have an excess of leaves, you can alternate mulching leaves on your lawn with bagging them up. Use the bagged ones as mulch on your vegetable garden. Additional local mulch sources may include a city’s yard waste collection site, a lumber mill for wood chips (make sure they have aged and dried for a season), or a feed mill or farmer for straw or marsh hay.
Be sure to apply 3 inches of mulch around vegetables and flowers. Mulch will not only add to the soil’s health as it breaks down, but it will also conserve water by reducing evaporation of water from the soil surface. Use of mulch provides a more even soil moisture for plants, thus decreasing stress. It also serves as a barrier against weed seeds, therefore you will have less weeding.
Creating composted material or organic matter is another sustainable and smart gardening practice. Make use of a backyard compost system in order to create your own organic matter. Something as simple as three 4×4 untreated wooden pallets fastened together will work. In here, you can place all of your vegetable scraps from the kitchen and excess yard waste.
It’s important to add the right ratio of carbon sources to nitrogen sources within your compost pile. The proper ratio aids in the decomposition or breakdown of this organic material by microbes which need to be present for your pile to work. Using a mixture of brown sources (carbon) such as fallen leaves or wood chips to green sources (nitrogen) such as leafy green plants will help your pile have the right ratio.
It’s also important to allow the pile to heat up internally to a temperature of 130-160 degrees. Be sure that the pile does not dry out during this time. Be sure to provide air to your pile by mixing it. Again, you can also seek out local sources of compost at city compost sites or perhaps a local farm may offer composted material for purchase. Some things to consider, especially for local pickup sources, is whether or not the material has been prepared properly to prevent weed seeds. Also, whether or not pesticides were applied would be difficult to determine with a city compost site collecting from numerous lawns.
Reducing the amount of tillage will also lead to healthier soil. Too much tillage breaks down the natural structure of the soil. Tillage also releases carbon into the atmosphere, thus upsetting the required carbon to nitrogen ratio that microbes within the soil need in order to live and continue the decomposition process that the soil relies upon. Use of mulch and addition of composted material with minimal soil disruption will help build you a healthier soil. It probably won’t all happen this year, but you can begin the process.
Other techniques for minimal tillage include use of root crops, such as longer radishes or turnips, to help break up soil particles and create air and water spaces. Check out the new Smart Soils video with MSU entomologist George Bird who highlights these important steps to a smart soil and shows us the living components within a healthy soil.
For more information on a wide variety of Smart Gardening topics, visit the Gardening in Michigan website at www.migarden.msu.edu or contact MSU’s toll-free garden hotline at 1-888-678-3464.
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FAQ
Can I mix soil and mulch?
Is it safe to mix bark mulch with soil? Yes, it is usually safe to mix bark mulch with soil, as long as it is done correctly.
What is the best mulch to mix with soil?
1. Compost Peat free compost is probably the best form of mulch as it contains a high level of nutrients. It retains a lot of moisture and is easily absorbed and taken down into the soil by beneficial bacteria, earthworms and invertebrates.
Can old mulch be mixed with soil?
It’s important to understand that old wood mulch should be mixed with compost before adding to your soil. Wood mulch mixed directly into your flower beds will compete for the nitrogen your plants need to survive.
Can you mix wood chips into soil?
Yes, you can use fresh wood chips as mulch, but there are some considerations to keep in mind: Nitrogen Drawdown: Fresh wood chips contain high levels of carbon, which can lead to nitrogen drawdown in the soil as they decompose. This means that they can temporarily tie up nitrogen, making it less available to plants.