Most people spread a layer of mulch around their landscape beds. Some even mulch vegetable gardens. With so many types to choose from, it’s often a confusing situation.
The main reasons we mulch are to conserve water, suppress weeds and just make the area look neat. Almost anything can suffice as a mulch. However, some fit certain situations better than others.
Some mulches are organic. Anything organic will eventually decompose. This can be a good thing or a bad thing, and the rate of decomposition varies greatly. Inorganic mulches generally don’t break down, but they often can get hot. This can be a problem around plants.
Hardwood bark mulch is probably one of the most popular organic mulches out there. Its greatest advantage is its availability. It decomposes faster than most types, but that can be an advantage, especially on sandy soils.
When this mulch breaks down it improves soil structure. That will help with both drainage and water holding capacity. More organic matter also means soils hold nutrients better. Decomposing hardwood mulch is usually not quite as acidic as pine mulch is. Again, this can be an advantage or a disadvantage.
A disadvantage of both types is that they need to be applied more often than most types. Many people like pine straw because it lasts longer and stays put nicely. It is also acid forming, so if that’s not a problem this might be a good choice. Pine bark nuggets can be attractive, but they are often displaced by heavy rains.
Decomposed sawdust or wood shavings are often used as mulching material. They have a problem in that they must be broken down by microorganisms. These bacteria and fungi require nitrogen fertilizer to break these materials down because these materials have a wide carbon to nitrogen ratio.
If this fertilizer is not added, these microbes will extract it from the soil. Consequently, nutrient levels in the soil can be greatly diminished. I recommend fertilizing and composting these materials before they are used.
Hay and straw are occasionally used, but they can contain weed seeds. They generally aren’t very attractive either, especially after a few rainy days.
Sometimes folks like to use weed barrier cloth on their plantings. This helps suppress weeds. It also makes the mulch last longer. Some folks also like to use the colored mulches as they maintain their appearance better.
Inorganic mulches are often the choice around areas where cleanliness and low maintenance the main goals. Crushed stone, river gravel, marble chips, volcanic rock and rubber mulch are just a few of the possible choices.
None are very conducive to plant health. They absorb heat and provide no nutrients or improvements to soils with poor drainage. They also won’t slow water movement on sandy soils.
Rubber mulch is a relatively new phenomenon. It’s often used on playgrounds because it provides protection from injuries due to falls. It does absorb heat and children might be more subject to burns than they would if people used organic mulches.
Mulching planting beds is important, regardless of the type used. Without some type of protection, soil erosion is bound to occur. We don’t need more sediment in our storm drains, nor do we need it in our waterways. Furthermore, planting beds simply don’t look attractive unless they have some type of finishing material on them.
Ted Manzer teaches agriculture at Northeastern High School.