The Virtues of Organic Mulch

By Andrea Laine

I used to look upon mulch as “icing on the cake” in my landscaped beds; a finishing touch that added visual benefit, but not much else. Boy, was I wrong! Mulch, especially the organic variety, is so valuable to vegetable gardens and flower gardens. Once I understood the wondrous things a mulch could do, I found it well worth the investment of time, energy and dollar to apply mulch every one or two years.

Herbaceous Border


Here are five benefits of using an organic mulch in your garden:

  1. Helps soil retain water – Mulch slows evaporation of water from precipitation or irrigation, which will help your plants weather hot, dry periods.  
  2. Reduces weeds  – A thick layer of mulch (two to four inches, no more) will prevent sunlight from reaching weed seedlings and block their growth. Weeds hardy enough to poke through mulch will be easy to spot and pull by hand.
  3. Insulates soil –  Mulch keeps soil cooler in summer–by as much as 10 degrees–and warmer during cool nights. During winter, mulch prevents the soil from freezing and thawing quickly minimizing damage to plant roots.
  4. Improves soil quality – As organic mulch decomposes, it enriches the soil below. Mulch also encourages earthworms to proliferate. Worms create spaces for air and water in soil and add nutrients to the soil via their castings.
  5. Protects soil from erosion and plants from disease – Mulch prevents plants and produce from coming in direct contact with soil. That helps protect the plant from soil-borne diseases and wet spots that may invite rot.  

When, What & How Much?

Mulch is best applied in the spring and/or in the late fall, after the ground has frozen. Various grades of pine bark or hardwood make good springtime mulches. Straw, shredded leaves, or pine needles make good fall mulch. Evergreen boughs are also useful as an overwinter mulch.
A coarser mulch, such as wood chips or nuggets, will last longer. You may be able to get away with replacing it every other year. Keep an eye on it, though; over time it can become compacted and begin to shed water. Gently cultivating it will solve the problem. A finer mulch, such as pine bark fines or triple-shredded hardwood, will break down faster thus improving the soil faster. It can do almost as much good as applying a layer of compost. The choice is yours to make depending upon the needs of your garden and personal preference.

Mulch For Gardening

Whatever type of mulch you choose, apply it in a two- to four-inch layer across your beds. Keep the mulch six to 12 inches away from tree trunks and plant stems. Without this breathing room, a plant may become too wet and invite disease or rot.  

You can purchase national brands of mulch at garden centers or buy it in bulk by the cubic yard* from a local distributor. These places typically sell sand, soil and compost in addition to mulches. Fresh wood chips are okay to use as mulch, so feel free to recycle a newly fallen tree from your land provided it is disease free.

Reap the Rewards

As you begin to prepare your spring gardening to-do list, consider working a mulch application into your plans. Your plants will be appreciative and reward you accordingly.

References & Resources

*Here is a step-by-step guide to calculating cubic feet/yards.

How to Mulch: Save Water, Feed the Soil, and Suppress Weeds by Stu Campbell and Jennifer Kujawski, Storey Publishing, North Adams, MA, Copyright 2015

Mulch, But Not Too Much

By now, you may have noticed piles or bags of mulch in landscapes all over the area. Last year, I wrote about some of the reasons why mulch is beneficial (see article here: However, you CAN have too much of a good thing with mulch.

Hardwood or pine bark mulch is a commonly used material in our area. Experts recommend adding a 2-3” deep layer around your plants, which helps to slow water evaporation from the soil, keeps soil temperature more even, and reduces germination of weed seeds, among other benefits. So, if 2-3 inches is good, would more mulch be better? The answer is no. Adding a deep layer of mulch can be harmful to plants. A thick layer of mulch may keep moisture from rain or irrigation from reaching the soil where plant roots are growing, limiting the amount of water the plants can use. During wet periods, a heavy layer of mulch can slow evaporation, keeping the soil waterlogged. Plant roots require oxygen as well as water. A heavy mulch layer can keep roots growing in the soil beneath from getting enough oxygen from the air. Oxygen starved plants will decline over time.


Photo: Cornell University

Trees are frequently victims of overmulching. The practice of piling mulch around trees forming a “volcano” of mulch is common but harmful. As mentioned in the previous paragraph, too much mulch can keep water and oxygen from reaching roots. To compensate, trees may develop roots in the mulch volcano, where oxygen and water are plentiful. These shallow roots grow through the mulched area and can circle the tree. As a tree grow in diameter, the circled roots can strangle the tree, causing decline and death.



A thick layer of mulch around a tree also can trap moisture around its bark.  Like all wood left in wet conditions, the tree bark will begin to rot over time. Decaying bark can be an entry point for fungi and bacteria as well as insects that can further damage the tree. That pile of mulch is the perfect cover for insects and rodents to hide while gnawing on trees, too.

How to KillaTree

To correctly mulch around a tree, keep the mulch a few inches away from the trunk of the tree. Many experts recommend mulching an area 3-4 feet in diameter around a newly planted tree, increasing the diameter as the tree grows.

If parts of your landscaping still have the recommended 2-3” layer of mulch, simply rake the mulch to give it a fresh appearance rather than adding an additional layer. This helps your wallet AND your plants.

-Ann Barnes


Like me, many Triangle homeowners are spending April weekends spreading mulch in their landscape beds. Mulch provides many benefits beyond simply making your yard look tidy and finished.


This is my mulch pile back in 2008. The older child is now able to help! I’ve learned a few things since then, including – 1) put a tarp under the mulch so you don’t lose much of it in the lawn, and 2) don’t let the kids climb on it.

A layer of mulch can keep the temperature of soil a bit cooler in summer and warmer in winter. Mulch helps to prevent runoff and erosion. It absorbs water, which then can move into the soil. It also slows evaporation of moisture from soil. It reduces soil compaction as a result of raindrops hitting the soil, and can help to prevent certain disease causing soilborne fungi from splashing up and coming into contact with leaves.

Mulch can prevent germination of weed seeds that are found in the surface layer of soil, so a Saturday spent spreading mulch will mean fewer hours spent pulling weeds later. Fewer weeds means that your plants will have less competition for resources such as water and nutrients.

Organic mulches (such as hardwood or pine) break down over time and release nutrients into the soil. Organic materials also improve the texture of our clay soils, resulting in more oxygen, moisture, and nutrients being available to plant roots. Inorganic mulches do not break down quickly and may not have to be reapplied as frequently, but they do not provide

Common organic mulches include shredded hardwood bark, pine needles, compost, leaves, pine nuggets, and hardwood chips. Inorganic options include rocks, gravel, landscape fabric, and recycled rubber. Black plastic is sometimes used, but not recommended because it doesn’t allow air or water to easily move to the soil below.  If you are not sure which mulch to choose, you can refer to the chart at the end of the article at this link:

The recommended amount of organic mulch to use is 2-4 inches around trees and shrubs, 1-2 inches around perennials, and 1 inch around annuals. Avoid piling mulch around the stems of plants, as this can encourage both stem rot and shallow root growth.

Additional sources:,

-Ann Barnes