University of Maryland Extension

FAQs - Mulch

too much mulch are base of tree

Mulch should not touch the trunk of a tree.
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Is there a way to test mulch? We have always purchased pine fine mulch, but this year’s delivery looks like regular hardwood mulch.

I never want to pull a weed again. I plan to put down black plastic weed barrier (or landscape fabric) and then put shredded bark mulch over that. All I’ll need to do it throw on some new mulch each year. Isn’t that a good permanent solution?

My husband and I are having a difference of opinion.  I prefer using red colored mulch in my perennial beds because I like the contrast of color between my plants and the mulch. My husband says that it is not natural and that it is not worth paying extra for. Who is correct?

We just bought some bags of wood mulch to use around our foundation plants. My son was helping me spread it when we realized that there were termites in some of the mulch bags. What do I do now? Should I have my house treated for termites?

I love using fall leaves as mulch my garden. My southern magnolia tree sheds a lot of leaves which I would like to grind up and use as mulch. However, people have told me that the leaves aren't good for the soil. What’s your take on this? Should I add lime or something?

Help! I have some strange looking yellow foam that is growing in the mulch.  I am afraid it is going to kill my plants. Do you have any idea what this might be?

Is there a way to test mulch?

Mulch is not a regulated product, so it is 'buyer beware' when purchasing mulch.  The best practice is to visit the site where you intend to buy the mulch and examine the products they have to offer.  Again, when the mulch is delivered, examine it before it is dumped from the truck.  If it is not what you ordered or not what you expected, you do not have to accept delivery.  Once they have dumped it, however, it is yours.

I never want to pull a weed again. I plan to put down black plastic weed barrier (or landscape fabric) and then put shredded bark mulch over that. All I’ll need to do it throw on some new mulch each year. Isn’t that a good permanent solution?

You’ll be creating a plastic mulch sandwich.  As the bark mulch decomposes to an organic material, you’ll end up with a layer of good “soil” on top of the black plastic. Weeds will grow quite happily in it.  Over the years, as you add more mulch, the organic layer will get deeper, and the black plastic will be buried deeper, rendering it useless. One option would be to remove the old mulch each year before you apply new mulch, though this robs your plants of all the good nutrients and benefits supplied by decomposed mulch. A better option is to simply use a 1-2 inch layer of mulch.

My husband and I are having a difference of opinion.  I prefer using red colored mulch in my perennial beds because I like the contrast of color between my plants and the mulch. My husband says that it is not natural and that it is not worth paying extra for. Who is correct?

Dyed mulch has come into favor the last few years. Actually colored mulch does not offer any advantages over conventional types of mulch but many people do find it aesthetically pleasing. Wood chips are dyed to enhance their ornamental value.  Technically you both are correct, color and composition are important when designing a perennial bed but the real purpose of using mulch is to conserve moisture, reduce weeds, prevent soil erosion, and to protect roots from the summer heat and the winter cold. Bark and wood chip mulches do look more natural. But again, everyone has their own personal preferences.

We just bought some bags of wood mulch to use around our foundation plants. My son was helping me spread it when we realized that there were termites in some of the mulch bags. What do I do now? Should I have my house treated for termites?

Not to worry.  Occasionally termite workers will infest bags of mulch. They are drawn to moist bags because they need moisture to survive.  Once the bag is opened and the mulch is spread the termite workers die. They need to be in a colony for long-term survival.  Termites are native insects, and we all have some in the vicinity of our homes naturally.  For this reason it is important to mulch properly; leave a 12-18 inch barrier of bare soil next to your foundation and do not have more than 2-3 inches of mulch around your plants.

I love using fall leaves as mulch my garden. My southern magnolia tree sheds a lot of leaves which I would like to grind up and use as mulch. However, people have told me that the leaves aren't good for the soil. What’s your take on this? Should I add lime or something?

Magnolia leaves are tough and decompose slowly, so they make a long-lasting natural mulch under magnolia trees. We have no idea why they would be a problem.  If you grind them up, you certainly can use them as mulch around other plants. Virtually all organic materials end up at a neutral pH of 7 after being composted, so acidity is not a problem and lime is not warranted to correct a low pH.  In fact, lime is not recommended for compost piles because it interferes with the microbial activity.

Help! I have some strange looking yellow foam that is growing in the mulch.  I am afraid it is going to kill my plants. Do you have any idea what this might be?

Yes, you have slime mold (also called 'dog vomit fungus') growing in the mulch. This is a harmless fungus that feeds on bacteria and other organisms that are found in mulch. These fungi will not harm your landscape plants. Leave it or scoop it into a garbage bag and put it out for trash pick-up. No other control is necessary.

Please send us a question at Ask the Experts if you have a mulch question you would like answered. Digitial photos can be attached to your question.

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