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14 Common Mulch Questions (Answered)

14 Common Mulch Questions (Answered)

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Paul Brown

Applying mulch to your garden beds is one of the most effective ways you can help your plants thrive. Mulch keeps weeds at bay, reduces water loss, moderates soil temperature, and adds organic material to the soil. Mulching is a win for both you and your plants!

In spite of all the benefits of mulching, though, it is not as simple as tossing some paper shreds or wood chips on the ground. Below are 14 common questions about mulch to help you determine the right type of mulch for you, how much you need, how often to refresh it, and more!

What is the difference between organic and inorganic mulch?

Put simply, organic mulches are materials that come from plants themselves while inorganic mulches are man-made materials that are not naturally occurring. 

Examples of organic mulch materials include grass clippings, dead leaves, wood chips, bark, cocoa bean hulls, pine needles, hay or straw, newspaper, paper shreds, or even compost. Inorganic mulch materials include plastic sheeting, landscape fabric, and stone (source).

How much mulch do you need?

In almost all cases, you will need enough mulch to create a two to four-inch layer throughout your garden beds. If your mulch material has a coarse texture, three or four inches of depth will be ideal. Materials that have fine textures will settle more tightly, so one or two inches will be plenty.

When in doubt, keep your mulch layers shallow, especially with new plants. When the layer of mulch is too thick, it can create problems such as root rot from soil that never dries properly. Start with a minimal amount of mulch and add to it as necessary until you find the depth that works best for your plants.

Should you water before or after mulching?

It is a good idea to water after you have applied your mulch. There are several reasons for this, including:

  • Lightweight mulch like straw, hay, newspaper, and paper shreds will settle more easily if they are watered after being laid in place. (See How To Shred Newspaper For Compost, Mulch, And Weed Barriers)
  • Mulch made from wood chips or bark needs a good, thorough watering after application to repel harmful fungi. If these types of mulch dry out and then stay continuously dry, they become a haven for fungi that can actually make the surface of the mulch water-repellent, which in turn makes irrigating your plants frustrating if not impossible.
  • Watering after you mulch can help you notice “trouble spots.” These may include places where the mulch is too thick for water to reach the soil, low spots where water tends to collect, or places where the soil may dry out too quickly.

How do you freshen up old mulch?

Before the start of each growing season, or throughout the growing season if necessary, “fluff” your mulch by sifting it with a garden fork. This will increase the airflow and keep your mulch from settling in such a way that repels water instead of letting it flow into the soil (source).

Depending on its age and condition, you may need to do more than simply fluff and freshen your mulch. Both organic and synthetic mulches decay over time, so you will need to be prepared to replace it.

How often should you replace mulch?

If you use organic mulch such as wood chips, bark, lawn clippings, or hay, you will likely need to add new mulch to your garden beds every spring. Only add enough new mulch to restore your mulch layers to your desired depth.

Landscape fabrics, plastic sheeting, and other types of synthetic mulch do not deteriorate quite as quickly as organic mulch. Depending upon your climate and other factors, you may find yourself replacing your mulch annually, but many are designed to last more than one growing season. Replace it as often as necessary for optimal plant growth, weed control, and aesthetics.

Should you remove old mulch before replacing it?

One of the upsides of using organic mulch, such as bark, wood chips, leaves, etc., is that it will break down and add nutrients and organic matter to your soil. For this reason, it simply does not make sense to remove the old mulch. If the old mulch has decomposed quite a bit, till it right into your soil; otherwise, simply fluff it and apply new mulch on top.

However, inorganic mulches, such as landscape fabric or plastic sheeting, add nothing to the soil as they deteriorate. Once they wear out or your plants outgrow them, you will need to remove the old materials before replacing them with something new.

Does mulch attract termites?

Mulch does not attract termites, but the termites who find woody mulch on their own while exploring the landscape will often make themselves at home. In other words, wood chip mulch makes a good habitat for termites, but they can’t sense the presence of mulch from afar. However, this does raise concerns about termites’ ability to move from your garden to your home. 

Avoid using wood chip mulch near the foundation of your home. If your garden beds are right alongside your foundation, move them or use a mulch that termites find less appealing, like hay, pine bark, or eucalyptus. If you notice signs of termites in your mulch, contact a local pest control professional for advice or abatement; do not treat your mulch with pesticide as you may unwittingly kill beneficial insect populations (source).

Can mulch ever be harmful to plants?

There are two cases in which mulch might actually do more harm than good:

  • Improper application. For example, if your mulch comes into direct contact with the base of a tree, you could inadvertently create a haven for rot and harmful bacteria. Similarly, mulch layers that are too thick or are volcano-shaped do not allow for proper irrigation, so your plants may become dehydrated even if you water frequently.
  • Toxic mulch materials. Shredded tires, recycled wood chips, and lawn clippings are all popular mulch choices, but all have the potential for harm. Shredded tires will leach toxic chemicals into your soil; wood chips can do this as well, if they were previously treated with toxic chemicals; and grass clippings that were previously treated with a broad-spectrum herbicide will harm any broadleaf plant they contact, weed or otherwise (source).

What is the best type of mulch for flower beds?

For your flower beds, organic mulch is the way to go. Landscape fabric (link to Amazon) or plastic sheeting will only be effective if your flowers are annuals. Perennials will soon be too large for the space allotted for them, and the sheeting will end up choking them.

Furthermore, organic mulches can return nutrients to the soil that will help your flowers thrive. For example, rhododendrons and azaleas are both acid lovers and often benefit from pine needle mulch that decreases the soil’s pH levels over time.

What is the best type of mulch for vegetable beds?

Because vegetables have different nutrient requirements than flowers, certain types of organic mulch can provide nutrient boosts while also protecting your vegetables from weeds. Untreated grass clippings, for example, can serve as an additional source of nitrogen, which is an essential nutrient for vegetable plants. Mature compost can also serve as both mulch and fertilizer in vegetable beds.

(See Compost vs Mulch: Make Sure You Know the Proper Use For Each)

Depending on the type of veggies you grow, black plastic sheeting may also work well. It is not as cost-effective as compost or grass clippings, but it may be worth considering if you grow veggies such as eggplants, melons, peppers, squash, or tomatoes.

What is the best type of mulch for trees?

Trees do best with organic mulches because these mimic the type of natural mulching that happens in a forest when leaves, pine needles, and branches cover the ground before decomposing. Leaves, pine needles, bark, wood chips, and cocoa bean hulls are all recommended mulch materials for trees. 

When you mulch around your trees, it is important to remember that, regardless of the material you choose, your mulch should not bury the root flare and come into direct contact with the tree’s trunk. Tree trunks are sensitive to rot, harmful soil-borne bacteria and diseases, and other problems that can be exacerbated by excessive moisture. Mulch can keep tree trunks too humid to be healthy, so be sure to maintain some space and airflow between the trunk and the mulch layer.

(See What Are The Signs Of Overwatering Plants?)

Does mulch color matter?

The color of your mulch makes some difference, but in most cases, you can reap the benefits of mulching regardless of color. These are the two instances in which the color of your mulch matters:

  • If you use plastic sheeting as mulch, it should be opaque black. Opaque black plastic will block sunlight, which will cut off the growth of weeds beneath it and prevent any weed seeds from germinating. Clear plastic, on the other hand, does not block the sunlight, allowing weeds to grow freely.
  • If you grow plants that are sensitive to high temperatures, use light-colored mulch during the summer and autumn to reflect heat and keep the soil a bit cooler. In the late winter and spring, dark-colored mulch can help the soil temperature rise sooner, allowing you to plant earlier and enjoy a longer growing season (source).

Do plants in containers need mulch?

If you keep your potted plants outdoors, adding mulch is a good idea. Containers tend to dry out very quickly, and mulch can help reduce the amount of water lost to evaporation. Furthermore, weeds can make themselves at home, even in pots.

In many cases, a two-inch layer of mulch will be sufficient for potted plants. See the above suggestions for the types of mulch that work well with flowers and veggies. 

Where can you buy mulch and how much does it cost?

If you choose to buy mulch rather than gathering leaves, lawn clippings, or pine needles for free, you can find mulch at lawn and garden stores and online retailers. It often comes bagged with each bag containing about two cubic feet. You can also buy landscape fabric and plastic sheeting from the same vendors. 

Prices vary by mulch type, brand, and retailer. In general, however, if you plan to buy bagged mulch, you can expect to pay $3.00 to $5.00 per bag. Landscape fabric is significantly more expensive, ranging from $13.00 to $120.00 per roll, not including the stakes, pins, or staples you will need to keep it anchored to the ground.

When you apply mulch correctly and maintain it properly, you are doing yourself and your plants a huge favor! The benefits of mulching far outweigh the maintenance efforts, and with so many affordable choices available, there is no reason to wait.