Mulches on Your Landscape

Between all the plants in your gardens that you have worked hard to place and nurture is open ground. With the help of mulch, these spaces can be an asset for weed suppression, soil moisture retention, aesthetic appeal, and eventual soil organic matter. Without mulch, it can be an invitation for unwanted plants and drying soil. Mulch is typically applied to planting beds, tree and shrub beds or rings, walking paths, and embankments, each of which will require slightly different applications.

Mulch can take many forms, though typically it is seen as an organic material. Here is a list of common mulches, and their advantages.

Compost – Adds soil nutrients and humus.
Wood chips/shavings – Informal/woods/functional sites with very good moisture retention and weed suppression qualities.
Bark mulch – The best combination of adding course organic matter, soil moisture retention, weed suppression, and oxygen exchange.
Buckwheat and cocoa hulls – Adds a trim appearance but limited other functions.
Straw- Use for new grass seeding as it shades new blades and limits erosion. Good under strawberry plants.
Black plastic – Only good for very long term weed suppression in plant-less open space.
Newspaper – Good, cheap weed suppression.
Pea stone/gravel – Path and drip edge use though weeds can still establish through it.

For the most effective mulching, the natural or naturally derived materials or combinations of them will prove best. A compost, bark mulch, and buckwheat hulls combination will provide very good nutrients with a lighter appearance. Two to four inches of these materials will last most of the season, with a light additional cover at the end of the summer to take your beds through the fall and winter. Remember, mulch is not directly for the plant. The one exception is that a mulch bed or ring will keep mowers and grass trimmers away from plants. Creating just a narrow mulch bed around fence posts will also keep mowers and trimmers away from them as they can suffer substantial wear over the years. Black plastic will substantially limit soil moisture and oxygen exchange and if it is covered by mulch or chips to mask the appearance, weeds will eventually grow on it. Dyed mulches give an appearance of something less than natural in a place where you might be attempting to create one.

Generally, the depth of mulch will be 1-4 inches with a lighter application for annuals, perennials, and smaller shrubs. Larger shrubs and trees will tolerate a maximum of about 4 inches between them. For both plant groups, the mulch should only lightly come in contact with the plant. At the bed edges, taper the mulch to meet the edge. In a new planting bed, spreading mulch is a careful process because of the small size and fragility of the plants. As the plants increase in size and heartiness and the mulch settles and becomes an integral part of the bed, this process will be much easier. Especially in the first season, the mulch may settle as much as half of the original depth, so adding more by the end of the season will be necessary. This will also be true especially if there are significant rains or if you have tenacious weeds.

There are some finer points to spreading mulch and it is important to heed them as they will effect how the mulch works. As you spread any mulch, take care not to compress it, usually by stepping on it. Compressing it will decrease water soaking into the soils and air movement through the mulch. You can help this situation by placing some flat stepping stones throughout your beds. Mounding mulch against a tree trunk, sometimes known as a mulch volcano, is an unnecessary and harmful tree mulching technique. Within a year or two, the tree bark will begin to rot, insects will infest, and small rodents will have a winter home and food. In addition, it is an added expense for extra material. If you are using wood chips or pea stone for paths and banks, you will need a little more mulch, 3-5 inches usually. Though it will be loose at first, these materials will settle and pack down over time to give firm walking traction. A caveat here is that if you use chips for paths around the home, some of it will track inside.

So step back from your new maple and think about what the base of that tree might look like in the woods; lots of forest floor duff, old leaves, broken branches, moss, etc. with more of this stuff decomposing underneath the loose top layer. Though in a simplistic way, this is what we are trying to imitate in an ornamental landscape.

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Grounds by Design – Fine Landscapes is locally owned by Matt Giroux, who is available for design, gardening, consulting, and photography on your landscape project. Contact Matt at 371-7093 with your gardening and landscape questions.