Does Mulch Prevent Weeds? Here’s How

Excessive growth of weeds is a problem that must be dealt with. Among the most common methods is, using mulch. But does mulch prevent weeds completely from growing?

Yes and sometimes, no. Yeah, you read that right. Using mulch does prevent weed or cannabis from growing, but how? The mulch layer stops the most crucial factor of weed plant growth from reaching the bottom, which is the sunlight. Without sunlight, it is simple to understand that there would be no weed growth. NO, in a sense that some weed plants still manage to break through the mulch barrier to get sunlight.

There is more to learn about this as to how does mulch works? Which mulch is the best? How to make mulch for weed control? And many more.

How does Mulch Prevent Weeds?

Before answering that question, let’s understand what mulch is? And how does it function? In simpler terms, the mulch is kind of an organic layer made of several different things like leaves, dust, grass, and many others. It is used for putting on top of the soil.

The reason being, to keep the soil moist, making the soil fertile and healthier, and of course, preventing the weeds from growing. Not always, but most of the time, the mulch is organic. Furthermore, it even increases the beauty of the garden area it is applied.

Now, the prevention part. The mulch is applied to the top-most layer of the soil. Due to it being organic, it benefits the soil in various ways, as it keeps its moisture intact and makes it healthier. After it is applied, the mulch prevents weeds from growing by blocking the sunlight, more or less, completely.

But there are some things to avoid while mulching, like being careful with the amount you are using. I mean that the excess or the deficiency will affect the mulching process. The ideal mulching density is about 3 inches thick. With this 3 inch layer, the sunlight would be blocked appropriately, making it difficult to reach the weed plants.

If the mulch is applied to the soil, it will stop the weed seeds from ever reaching it. That means without the soil, the weed seeds won’t be able to grow.

By doing so, you will see a significant reduction in weed growth. Also, consider keeping the mulch slightly, like an inch, away from any of your plants because otherwise, it will harm your plant severely by keeping the moisture. Organic is among the most common mulch used to prevent weeds. So, sooner or later, its organic materials will get mixed with soil and become thinner. Add an extra inch of mulch once or twice every year.

Why does Weed Grow through some Mulch?

The mulch’s job is to block the sunlight from reaching the weed or cannabis seeds in the soil. So if it is preventing the sunlight from going down, why does the weed still grow? And sometimes even through the mulch itself?

This question’s answer lies in the previous subheading, where we talked about the simple mistake of people applying the mulch in either more than necessary or less than needed.

If the applied mulch’s layer is relatively thinner or of low density (less than 3 inches, around 2 inches or so), that means some vigorous weeds will still make their way through the mulch and get the necessary sunlight to grow. That is why sometimes weed grows through some mulch.

What’s the Best Mulch to Prevent Weeds?

A study shows that different types of mulch have different effects. Simply put, the mulch type influences plant growth, be it an ordinary plant or a cannabis plant. That is why you must choose the best mulch for your garden.

Before that, ask yourself what the reason for mulching is? Which type of garden do you have? Where will you apply it? If you have answers to these questions, you may learn about the best mulch.

Organic mulch is often considered the best because it gets mixed with the soil to improve its health when it decays. You can also use straws for mulching, but the straw itself has some cannabis plant seeds. Or you may use tiny stones for this purpose, but as you can guess, they won’t decay to benefit the soil.

Can you Mulch over Weed?

That is a Yes and No again. Yes, you can mulch over weeds to prevent their growth. If the weeds are at their beginning phase and not yet have made a firm position in the soil, mulching over them will prevent sunlight, and eventually, they will die. Or, if you want to be 100% sure, consider handpicking the weak weeds before mulching.

The same method cannot be applied to weeds that are well-rooted. You will have to remove those weeds by either pulling them or spraying herbicides over them before mulching that area of your garden.

Tip for Effective Weed Control with Mulch:

1. Thickness:

As mentioned above, the thickness of the mulch must be around 3 inches or 7.6 cms. Anything density lower than this would be insufficient for blocking the sunlight.

2. Type:

Mulch has two types: Organic and Inorganic. The inorganic mulch is good for the short term but not ideal, as it will not decompose to benefit the soil. Whereas the organic mulch will decompose with time and be mixed with soil to improve the soil’s health.

3. Remove weeds before mulching:

The weeds that already have strong roots inside the soil need to be removed first for mulch to function correctly. Or else, these vigorous weeds will penetrate through the mulch and keep surviving.

4. Applying Weed Control before mulching:

Those strong-rooted weeds will affect the mulch’s performance. So, consider handpicking the weeds or spraying weed killers on them before mulching.

5. Applying covering before mulching:

You can use fabric or plastic as covering before mulching as it will provide an extra layer and additional barrier for weed to grow and cause any problem.

Can you Spray Weedicide On Mulch?

You can do it. Because sometimes, you just spray over the mulch to freshen its color and make it look new and healthy. But it does have its drawbacks, as spraying weedicide on mulch will destroy the essential nutrients present in the soil.

Furthermore, spraying weedicide will have severe effects on the mulch’s decaying, as its beneficial nutrients are killed off by the weed-killing chemical. Thus, mulch decomposition will have no positive effect on the soil’s health. So, can you spray weedicide on mulch? No! It is not ideal to spray your mulch.


Mulching is considered to be the best method to prevent weeds from growing and surviving. Weeds are a problem for your garden, that is a fact. You can use other ways to stop their growth, but mulching is said to be the most natural one.

If you follow the instructions for its uses properly like how thick the mulch should be, which type is the best, how to use it over your garden, then you will see a significant decrease in their growth. Be careful though, as one should not make it overly thick or extremely thin either, because in both cases, the result will be negative.

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