How to Select Landscape Mulch

Advantages and Disadvantages of the Different Types, Plus the Acidity Question

Straw mulch and drip irrigation around vegetable plants in garden.
Straw may be the mulch with the most advantages to offer. Francesca Yorke/Photolibrary/Getty Images

When determining which landscape mulch is best suited for your landscaping needs, there are many factors to consider. The question can best be tackled by presenting the various types separately, but judging each based on the same criteria. All have their advantages and disadvantages. The following types will be evaluated here:

  1. Straw
  2. Hay
  3. Leaves
  4. Stone
  5. Black plastic
  6. Wood-based (that is, bark, chips, sawdust)
  1. Pine straw

Before beginning, let's look at a preliminary question that many landscaping enthusiasts have: How does landscape mulch affect soil pH? More specifically, does any type of mulch lower soil pH, as many have long suspected in the case of pine needles?

Can Your Choice of Mulch Make Your Soil More Acidic?

The composition of your soil pH has a hefty impact on plant health. Since landscape mulch could influence that composition as it decomposes, it's understandable that people have often expressed concern over how mulch selection impacts soil pH. Does the use of pine needles lead to an acidic soil, for example? What about oak leaves?

A view that you will come across more and more (although there is plenty of room for disagreement, especially as new research comes in) in your reading is that landscape mulch has a minimal impact on soil pH (although, if you wished to be on the safe side, it would not hurt to avoid using the same type year in and year out).

Also, while oak leaves may be acidic when fresh, experts such as David J. Williams now say that "the net result is an alkaline reaction," as they decompose. Furthermore, it is now generally thought that pine needles lower soil pH to only a negligible degree, if at all. And whatever possibility exists for acidification pertains only to uncomposted pine needles.

Composting neutralizes them.

Nonetheless, it couldn't hurt to rotate between materials traditionally deemed "sour" and those thought of as yielding "sweet" soil; and just to be on the safe side, have your soil tested occasionally.

With the question of the potential impact of landscape mulch on soil pH out of the way, let's reflect on some other issues surrounding mulch selection -- some of which are quantifiable, others of which boil down to personal landscaping preferences. We will have to prioritize in order to make a decision, since a mulch that scores high in one category might perform miserably in another. Two obvious uses of mulch to which the reader will find little or no reference in this article are weed suppression and erosion control. They have been omitted for a simple reason: Any landscape mulch employed properly will cut down on weeds and erosion. These are the two constants in this discussion.

Preliminary Notes About Mulching

  • "Insulation value in summer" is judged by the degree to which the mulch can keep the soil beneath it cool and moist. A successful summer insulator will both reduce the need for watering and protect roots against extreme heat. Clematis vine is an example of a plant that benefits greatly from having its roots kept cool in summer.
     
  • The consideration of whether or not the mulch needs to be removed in spring is grounded in the fact that heavy organic mulches can smother emerging spring plants. This is obviously less of a factor, however, for plants that remain alive above-ground, throughout the winter. But even the latter can profit from having the soil around their roots warmed by the spring sun, a process facilitated by the temporary removal of the mulch. In the case of plastic sheets (or landscape fabric, for that matter), this factor is irrelevant, since holes are poked through the material to provide access for the plants.
     
  • "Nourishment and aeration afforded to underlying soil by decomposition" is one of the criteria used in the following pages to compare the various landscape mulches. Decomposition will be hastened as you work the mulch into the soil (whether intentionally or unintentionally) when you cultivate around plants (especially if you do so with a rototiller). However, do not be fooled by the word "nourishment" into thinking that compost and mulch are synonymous; they are not.  

    Now let's begin comparing mulching materials in earnest, beginning with a landscape mulch very popular in the southern part of the U.S. We'll also look at the bark and plastic types.

    Mulch Choices: Pine Straw, Bark, Black Plastic

    After the initial considerations discussed above, it is time to compare the various types of landscaping mulch, to determine their advantages and disadvantages. Let's begin with pine straw mulch, a product sold in bales. The needles are harvested from plantations -- a huge industry. Most of it comes from the southern U.S., where its use is also commonly used in landscaping.

    Pine Straw Mulch

    • Appearance: Pine straw mulch provides the reddish-brown color (although less vivid) that redwood bark mulch offers.
    • Insulating value in summer: Good
    • Insulating value in winter: Good
    • Need to remove in spring: Yes
    • Nourishment and aeration afforded to underlying soil by decomposition: Fair
    • Allows water and oxygen to move freely into the soil: Excellent
    • Ease of application and maintenance: Good

    Wood Chips, Sawdust, and Bark Mulches

    • Appearance: Good
    • Insulating value in summer: Good
    • Insulating value in winter: Good
    • Need to remove in spring: Yes
    • Nourishment and aeration afforded to underlying soil by decomposition: Fair
    • Lets water and oxygen move freely into soil: Good
    • Ease of application and maintenance: Good

    Black Plastic Mulch

    • Appearance: Poor, unless you are striving for that "hi-tech" look.
    • Insulating value in summer: A mixed bag here. Black plastic mulch keeps the moisture already in the soil from escaping, but it also heats up the ground considerably.
    • Insulating value in winter: Fair
    • Need to remove in spring: No
    • Nourishment and aeration afforded to underlying soil by decomposition: None
    • Lets water and oxygen move freely into soil: No
    • Ease of application and maintenance: Excellent

    Next, let's look at further choices for landscaping mulch.

    Qualities of Stone Mulch, Plus Leaves, Hay, and Straw 

    Like the plastic mulch we looked at earlier, stone mulch is an inorganic option, even though it is natural.

    Due to its ruggedness, stone (for example, crushed stone) is particularly effective for landscaping with dogs: It holds up to their unique brand of foot traffic (paw traffic).

    Stone Mulch

    • Appearance: Good, if used around trees, cacti and succulents. But stone mulch may not be aesthetically appropriate for vegetable or flower gardens. This will be a subjective decision.
    • Insulating value in summer: Fair. Stone mulch tends to heat up, but it also retains much of that heat within itself.
    • Insulating value in winter: Fair. Again, while stone mulch easily grows cold, at least it keeps much of that cold off your soil.
    • Need to remove in spring: Yes
    • Nourishment and aeration afforded to underlying soil by decomposition: No nourishment, fair aeration
    • Lets water and oxygen move freely into soil: Yes
    • Ease of application and maintenance: Fair. Leaves get caught between the rocks and must be removed. Otherwise, they decompose and become soil, in which weeds can sprout.

    Mulching With Partially Composted Leaves

    • Appearance: Fair
    • Insulating value in summer: Excellent
    • Insulating value in winter: Excellent
    • Need to remove in spring: Yes
    • Nourishment and aeration afforded to underlying soil by decomposition: Excellent
    • Lets water and oxygen move freely into soil: Fair (unless leaves are very finely shredded, in which case they will rate better in this category).
    • Ease of application and maintenance: Fair

    Straw and Hay Mulches

    • Appearance: Straw brightens your area nicely; hay is less attractive, but it provides a softer look (and feel).
    • Insulating value in summer: Excellent
    • Insulating value in winter: Excellent
    • Need to remove in spring: Yes
    • Nourishment and aeration afforded to underlying soil by decomposition: Excellent
    • Lets water and oxygen move freely into soil: Excellent
    • Ease of application and maintenance: Fair
    • Note: Straw is preferred over hay, because the latter tends to be riddled with weed seeds.
    • Note: Straw is one of the best mulch choices for winter protection, due to its insulation potential. Being hollow, each strand of straw provides dead air space -- perhaps the #1 characteristic of an effective insulator.