Can You Fertilize on Top of Mulch?

The straight answer to this question is – yes, you can fertilize on top of mulch. Yet, there are some factors to consider, such as the type of fertilizer you are using and how fast your type of mulch decomposes. 

As well, timing is crucial when you apply fertilizer to different kinds of mulch – and we’ll run through these processes more specifically in this guide. Plus, there are some instances where it’s better to add fertilizer first before re-adding new mulch.

Anyhow, let’s delve a little deeper and look at the various options you have to work with…

How to use Fertilizer with Mulch

If it’s the first time you are using mulch, use fertilizer first. It’s a lot more difficult for your plants to extract all the fertilizer nutrients if there’s mulch blocking all the good stuff from getting to them.

However, for those that have already added mulch but want to add fertilizer, there are a couple of general rules to follow:

  1. Apply granular or liquid fertilizer on top of old mulch in gardens where much of the mulch has decomposed to around twelve inches – ideally less. Then you can go about covering the area with a fresh mulch layer once more. As well, add at least two to four inches of mulch to prevent weed growth. 
  1. Don’t use granular fertilizer in gardens and fields where a large amount of mulch exists – typically anything above 12 inches. Instead, treat all of your plants and tree roots with a liquid fertilizer so that the nutrients can soak through the mulch and feed them adequately.

Slow vs. Fast-Decomposing Mulch

This is where the timing aspect of how to use a fertilizer with mulch is essential. Plus, the types of fertilizer used need to be carefully chosen to ensure your garden can remain nourished.

It can be more challenging to apply fertilizer over mulch that decomposes slowly, such as bark, wood chips, or nutshells. A liquid fertilizer that penetrates mulch well should be considered in this instance to provide your plants with all the nutrients they require. However, if the slow-decomposing mulch has decomposed enough, a standard fertilizer might just work fine.

Keep in mind: Bark generally takes seven to ten years to decompose, and wood chips five to seven years! 

If you don’t want to use liquid fertilizer, there is another option to remove slow-decomposing mulch like bark or wood chips. Either take away all of the mulch, which can be time-consuming or just remove it in key areas. 

A rake can help with the removal process, and it doesn’t have to be totally removed. Just make sure you’ve left enough open space in your key areas to add your fertilizer where it can be effective.

Ideally, fast-decomposing mulch will need to be reapplied every spring. Since much of the mulch in your garden would have broken down by this time, fertilizing before applying fresh mulch is a brilliant idea. With little effort, you can fertilize and then your new mulch layer for an easy day’s work.

Keep in mind: Grass clippings fully decompose the quickest at a rate of between one to six months. Straw takes about one to two years to break down, and cocoa shells are sort of in-between at around two to three years.

Ultimately, it’s up to you to determine whether your mulch is decomposed enough for you to just add fertilizer over the top – instead of the other methods we just described.

Can You Add Compost on Top of Mulch?

Applying compost directly to your soil, much like any other fertilizer, is always going to be the best way forward. It makes for the most immediate and robust source of nutrients for your plants and trees. 

However, in certain scenarios, you can layer compost on top of mulch. Again, it all depends on the type of mulch being used and your choice of fertilizer.

Here are a few guidelines to follow:

  1. With areas that only have around half an inch, or thoroughly decomposed mulch, add a good 2 inches of compost on top and then add your new mulch layer.
  2. Rake aside thicker layers of mulch and remove as much as you can before adding your compost layer so that the soil can gain its proper benefits. Then you can add your fresh mulch layer.
  1. Do not apply compost to thick layers of mulch – no matter how much it has decomposed. If left like this, it gives a chance for weeds to take root as your plants won’t get the nutrients they need to compete.

Additional tips: Make sure there are no weed seeds mixed in with your compost pile. Also, a good way of collecting compost through your lawn care routine is to use thatch you collect once or twice a year. Plus, plugs that come out of the holes you make when using an aeration tool can be added to the compost heap too.

Does Mulch Tie up Nitrogen in the Soil?

It’s a common myth that mulch can bind nitrogen in your soil, causing your plants to suffer. In reality, nutrients in mulch combined with soil increase in the roots as well as in plant foliage. 

There is actually less nitrogen at the thin topmost layer of the soil, just below the mulch, which is a good thing. The thin low nitrogen layer inhibits weed seed germination, so all-in-all, don’t fret about mulch and nitrogen issues.

Does Mulch Fertilize the Ground and Soil?

Some have deemed wood chips to be one of the best mulches to use. It loosens compact soil areas, adds organic elements, keeps good moisture levels, and gradually adds nutrients to the soil over time. 

In fact, wood chips can be a better alternative to fertilizers because, for example, compost can sometimes add too many nutrients. And believe it or not, if your soil is too nutrient-rich, then it can become toxic and actually kill your plants!

The Bottom Layer

You can fertilize on top of mulch, but it’s only advisable to do so if you are layering over decomposed mulch or a very thin layer.

It’s a better idea to remove or distribute your mulch out a little and then apply your fertilizer. Or, you can opt for a liquid fertilizer, which will be less effort overall. 

Either way, follow the guidelines we mentioned, and you should be good to go!

Sources:

  1. http://www.soilquality.org.au/factsheets/soil-nitrogen-supply
  2. https://www.britannica.com/science/seed-plant-reproductive-part/Germination 

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