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Mulch What It Is, Why It Is Important, How To Apply It

Kristina Howley for Proven Winners ColorChoice Shrubs
Photographs courtesy of Proven Winners ColorChoice Shrubs

Mulch is a common element in a garden. It serves an aesthetic purpose as well as many practical ones. When faced with covering a whole bed, it can be hard to decide what material to use, how much to apply, and what to do when it’s been there a while. Let’s cover the facts so you can get back to enjoying your garden!

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Why Is Mulch Important?

Beyond providing a uniting element throughout a garden space, practically speaking mulch:

  • Helps the soil retain moisture.
  • Keeps the soil temperature more even, insulating the roots against temperature swings.
  • Prevents weeds from popping up in great numbers.
  • Makes it easier to pull any weeds that do try to grow.

Types of Mulch

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Organic Mulch

This type of mulch breaks down over time and comes from the earth. Most often, it’s best to use what is locally available.

  • Bark or woodchips
  • Shredded leaves
  • Pine needles

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Inorganic Mulch

This type of mulch does not break down and may be man-made.

  • Rocks or gravel
  • Plastic chips or sheeting*

*We do not recommend using plastic sheeting. Learn why in this article.

How to Apply Mulch

Plan to place a two- to three-inch (5-7 cm) layer of mulch over the soil surface of your garden bed. Using a thinner layer of mulch will not provide the same benefits to your plants and soil that we listed above. A thicker layer of mulch may end up collapsing onto your plants, burying the stems and causing the plants problems. You can apply mulch in a thicker layer if there aren’t any plants present to worry about.

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Use this handy calculator to determine how much mulch you need to buy.

What to Do with Old Mulch

Organic mulch will break down over time. This is great! It adds to the topsoil layer of your garden bed. New mulch can be applied on top of it. If you spread woodchips or bark mulch every year, you may find at some point that it is too thick and full of organic material. In this case, you can rake it off and either put it in a yard waste bin or pile it up in an out-of-the-way spot in your yard. You can do one of two things with this pile:

  • Let it sit there to break down into soil to use as necessary.
  • Rake out the intact pieces of wood and set them aside to use as mulch again. Add the organic material to a yard waste bin or compost pile.

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If you have stone or gravel mulch, try to make it a priority to clean it out regularly. When organic matter falls into these beds, it can quickly become stuck and degrade, making a perfect place for weed seeds to take hold. It’s easiest to use a leaf blower to get debris out of the crevices. A rake can also work, but the process takes more time and may break the organic matter into smaller pieces.

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Frequently Asked Questions About Mulch

Should I mulch before or after I plant my flowers?
If you’re planning a new bed, it’s best to mulch after you’ve planted it. That will keep the process much neater. 

What do I do if I want to plant something new in a mulched bed?
Brush aside all of the mulch in the area where you’ll put the hole and as much space as you’ll need to set the soil that comes out of the hole.

Will my flowers from bulbs come up through the mulch?
Yes they will. No need to worry about pushing the mulch aside for them, the plants will push up through it.

Where should I put my mulch when it’s delivered?
It’s best to have your mulch in a driveway or on a level, non-organic surface. If a huge pile of mulch is dropped directly into the garden, it may damage plants.

How long does mulch last?
If you choose an organic mulch, the timeline varies. Hardwood mulches last a long time, while leaf mulch degrades pretty quickly. You can generally count on it lasting four to six years, but folks often refresh it every other year, or every three years.

Can I apply fertilizer over my mulch?
To get the best results with granular fertilizer, you should move the mulch away from the rootball of the plants and put the fertilizer directly on the soil surface. Then water it in. Water soluble fertilizer can be applied directly over a mulched soil surface.

What is the best mulch?
The best mulch is the type that you can get sourced locally and sustainably. If possible, get a hardwood product so that it will break down as slowly as possible.

How do I use leaves as mulch?
Collect fallen leaves in the autumn and mow over them a few times to break them into smaller pieces. Put them in a big pile to decompose a bit over the winter. Be sure it’s situated in a spot that will receive periodic rainfall. Turn the pile a few times. If the pile is nicely decomposed, you can use the leaf mulch the following spring. If the leaves are still firm and look intact, keep turning the pile occasionally and use the mulch in the fall or the following spring. Apply it in a two- to three-inch (5-7 cm) layer.

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