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Once it has started, mulch fungus can be difficult to get rid of, and it should be treated as soon as the problem arises. Many gardening experts agree that the best way to deal with mulch fungus is to prevent it from happening in the first place. If your mulch does develop fungus, you can remove the affected portion and replace it with a new layer of mulch. Other methods for treating mulch fungus include heat treatments, pH-changing agents, or fungicide treatments.
Some people simply add a new layer of mulch over the old layers to get rid of mulch fungus. This method often fails, though. Doing this will usually just result in the fungus popping up into the new layers.
If there is any type of mold or fungus growing in your mulch, before adding a new layer many experts advise that you do a few things first. The first thing that you should do whenever you notice that you have a mulch fungus is to remove it. This will help prevent spores from spreading and prevent new crops of fungal growth.
After all of the fungus and surrounding mulch has been removed, you can rake away the top layer of mulch. Discarding both the mold and the top most layer of the mulch will help in preventing new growths of mulch fungus. In particularly bad cases though, all of the mulch may need to be removed.
After the mulch has been removed, turn the soil underneath. You can then add a new layer of mulch. It is important to remember not to have too much mulch, as thick layers can actually encourage certain types of mulch fungus and mold to grow. Many experts believe that one to two inches of mulch is ideal.
One way to kill mulch fungus is to heat it to a temperature of roughly 104 degrees F (40 degrees C). This can be accomplished naturally. To use this method, all or at least most of the mulch must be removed and piled in sunny area. Wet the mulch thoroughly and wait at last a couple of weeks. This will cause the decomposition process to start, which will cause the mulch pile to heat up to temperatures high enough to kill most mold and fungus colonies.
Raising the pH of the mulch and soil can stop many fungal growths completely. Because many fungal growths prefer slightly acidic soil, "sweetening" the soil, or making it less acidic, can work. This can be achieved by adding liquid lime, which can be purchased in the gardening section of many larger chain stores. Sprinkle or spray a small amount of this mixture directly onto the mulch. Be careful not to get it on any plants and not to use too much, as it could possibly be damaging.
Fungicides are also a solution to mulch fungus. Many all-purpose fungicides for gardens are on the market today. Be very careful if you use this method, and follow all directions on the package precisely.
Safer, more organic fungicides may be a better option, considering they are safer for humans and animals and have less of an impact on the environment. Two organic alternatives are cornmeal and regular baking soda. Just about any type of cornmeal will do. To use it, simple sprinkle it over the mulch and water, or soak one cup in one gallon of water and spray or pour onto the mulch. Baking soda can be used in much the same way, only using two tablespoons of it in one gallon of water.
Typically, preventing garden fungus on organic mulch is easier than getting rid of it. Generally, hardwood mulch is more prone to certain types of fungi, and should be avoided. Softwood mulches, such as those made out of pine are often considered better, along with pine needles and other organic materials. Other tips to avoid mulch fungus include turning it frequently and not allowing it to become too wet or dry. Both wet mulch and dry mulch can promote fungal growths.
@Vincenzo -- using that method will actually help create an environment in which fungus likes to grow. Think about it -- the problem with black plastic bags is that they make it difficult for moisture to escape the garden bed. Fungus just loves moisture and will be more likely to crop up in that scenario. For weed prevention, you're better off with a "weed mat." Those do help ward off weeds and have holes in them so that water can escape into the soil and fungus is less likely to attack plants at the roots.
Around these parts, a lot of people start off their gardens by lining the garden bed with plastic (often black plastic garbage bags), covering those with dirt and then adding mulch after the plants are in place. The goal of doing that is to prevent weeds.
Will using that technique also prevent mulch fungus?
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