Can You Fertilize On Top of Mulch? [A Detailed Guide]

Know the conditions and process for fertilizing atop mulch for the best results. Also learn the types of fertilizer you can apply on top of mulch.

By
Sean Stratton | Updated January 21, 2023
fertilize garden bed with plants

Yes, you can apply fertilizer on top of mulch. Your success will depend on the type of fertilizer, the mulch you are using, and the decomposition rate of the mulch.

To save your pretty garden bed and all your hard work, read on to learn more facts about fertilizing on top of mulch.

Conditions to Fertilize on Top of Mulch

Type of Mulch:

The type of mulch is the first thing to keep in mind while thinking of applying fertilizer on top of it. We can categorize mulch into two types.

  • Fast-Decomposing Mulch: This type includes leaf mulch, grass clippings, seed hulls, etc. These mulches decompose comparatively faster.

If you are considering applying fertilizer on top of the previous year’s mulch in the new year’s mulch application season, don’t hesitate to do it because most of these mulches would already be decomposed by then. This indicates that you can use fertilizer on top of the fast-decomposing mulch.

  • Slow-Decomposing Mulch: This type consists of traditional organic mulch made using bark, nutshell, wood, or wood chips.

Slow-decomposing mulch will decompose slowly, so, applying the fertilizer directly on top of this mulch may not work as efficiently as those fast-decomposing mulches. Bark mulch can take up to ten years, and wood chips mulch can take up to seven years to decompose. So, you are probably getting an idea why regular fertilizer applications may not work.

However, you can apply the fertilizer by raking the mulch aside. Though you don’t need to strip all the mulch, it’s still a lot of work.

Type of Fertilizer:

  • Liquid Fertilizer: When talking about applying fertilizer on top of the mulch, the best option would be to use liquid fertilizers. The liquid will make its way to the soil and provide nutrients to your plants even if you use them on top of the slow-decomposing mulch.
  • Granular Fertilizer: This type of fertilizer may not work directly on the slow-decomposing mulch, mainly if the mulch is not decomposed enough because granular fertilizers need to get in direct contact with the ground to provide the best results.

This may work on almost decomposed mulch, but the best thing to do is rake some mulch aside and ensure that the fertilizer touches the wet soil to release the nutrients efficiently.

So, now you know which conditions will allow you to apply the fertilizer directly over the mulch and in which cases you need to rake the mulch and apply the fertilizer.

Also Read: What Does Epsom Salt Do for Tomatoes

Can You Put Granular Fertilizer on Top of Mulch?

You should not apply granular fertilizer on top of mulch. Granular fertilizers require direct contact with the soil to work correctly. So, if you put it on top of mulch, the mulch will make a barrier between the soil and the fertilizer. As a result, you will not get satisfactory outcomes from your fertilizer.

If you have no choice except to use a granular fertilizer, make sure to rake some mulch before applying the fertilizer. This will help the granular fertilizer to get in direct contact with the soil and allow it to release its nutrients.

Can You Put Osmocote on Top of Mulch?

Osmocote fertilizer needs to be in direct contact with the soil. So, if you were to put it on top of the mulch, chances are that you don’t get satisfactory results.

You can pull some mulch around the base of the plant, apply the fertilizer, and put the mulch back again. But you can also apply the fertilizer on top of the mulch and let irrigation water or rainwater do the job for you.

However, this will depend on the size of mulch your garden bed has. If the garden bed is covered with a thick layer of mulch and you apply Osmocote on top of that, you may wait a long time and see no changes in your plants.

Also, note that this may cost you a lot of fertilizer because the coarse mulch will trap the fertilizer. And even if you apply it on top of thin-layered mulch, you’ll still lose a lot of fertilizer. So, using Osmocote directly in the soil is recommended.

Can You Add Compost on Top of Mulch?

Avoid applying compost on top of mulch. You will get the best results if you apply compost to the soil and cover it with mulch afterward.

But you can apply the compost over the mulch if it is half an inch or less thick. First, apply the compost. The ideal thickness of compost is two inches. After that, apply the new layer of mulch on top.

If the mulch layer is thicker than half an inch, rake the mulch aside, try to expose the soil as much as you can, apply the compost, and add a new layer of mulch on top of everything.

If you apply a layer of compost over a thick layer of mulch, weeds may appear. So, applying compost directly to the soil is the best option.

Can You Liquid Fertilize on Top of Mulch?

Yes. First, you must ensure the mulch layer is not too thick. A thick layer of mulch can make it difficult for the fertilizer liquid to reach the soil.

Don’t forget to water thoroughly after applying the liquid fertilizer. This will help the liquid to reach the soil. Again, the best practice is to use any fertilizer directly on the surface. So, if you want the best results, you can rake some mulch and apply the fertilizer directly.

How to Fertilize on Top of Mulch

We’ve discussed the types of mulch and fertilizers that allow you to fertilize over the mulch. Now, let’s look at the process of fertilizing on top of mulch.

Choose the best time to apply the fertilizer. This will depend on the type of mulch you are using on your garden bed. If the mulch is fast-decomposing, you can apply the mulch every year.

The best time to apply fertilizer is before placing a new layer of mulch in the spring. You don’t need to worry too much about the previous year’s layer of mulch because most of that would have been decomposed by that time.

If your garden bed has half an inch or less of mulch remaining from the previous year’s mulch, you can apply liquid or granular fertilizer over that without any hesitation. After that, you can apply the new layer of mulch.

The scenario will be different if you used slow-decomposing mulch on your garden bed. Applying a regular fertilizer may not be effective in this case. Plus, if the remaining mulch is more than half an inch, using granular fertilizer is not recommended. Instead, apply a liquid fertilizer to provide nutrients to your plants.

Ways to Fertilize with Rock Mulch

  • Foliar Application: This is the easiest option. You can use a foliar fertilizer and spray it directly on the plant.
  • Fertilizer Spikes: You may use a fertilizer spike and push it into the soil.
  • Diluting the Fertilizer: Dilute a water-soluble fertilizer in water and pour it into the root area of the plant.
  • Fertilizer Injector: You can buy a fertilizer injector to fertilize your plants. One point to note here is that the amount of fertilizer for a plant will depend on the amount of water it gets. The plants that get less water will get less fertilizer than other plants.

Fertilizing Through Wood Chips

Wood chip mulch is slow-decomposing mulch. So, the best thing to do while applying fertilizer is to rake the mulch from the base of the plant or the key areas first, then apply the fertilizer.

However, if it is a must to apply the fertilizer over the wood chips, like in the case of a large garden, you can choose a liquid fertilizer and water thoroughly after applying it. Do not use granular fertilizer over wood chips.

Common Questions

Does Mulch Tie Up Nitrogen in the Soil?

Mulch does not tie up enough Nitrogen in the soil to cause a deficiency in your plants.

This question might be expected for wood chip mulch. If you use wood chips like soil amendment, this may cause Nitrogen depletion, but if you simply lay the wood chips as regular mulch, this will cause a little bit of Nitrogen depletion on the surface, which is nothing to worry about, and you can just ignore it.
The topmost layer is the place where the seed germination of weeds takes place. So, a good thing about Nitrogen depletion on the surface caused by mulch is that it’s helping to prevent weeds from peeking into your garden bed.

The mulch will gradually return more Nitrogen than the amount of Nitrogen it took from the soil. So, it’s a win-win for you anyway.

Do I Need to Remove Mulch before Adding Compost?

You don’t need to altogether remove the mulch, you can simply pull back some mulch from the base of the plants or your selected areas, add the compost, and return the mulch to its place afterward.

Final Words

When discussing fertilizing plants, the best thing to do is apply it directly to the soil. This benefits the plants the most.

However, if you apply the fertilizer over the mulch, ensure it’s almost decomposed and the layer is very thin. If the layer is thick, regular fertilizers are more likely to cause no significant beneficial effects on your plants, but liquids may come in handy here.

Written by Sean Stratton

Sean Stratton

Hi, I'm Sean, the senior editor here at Fertilizer Pick. I grew up on a farm in North Carolina and have grown fruits, vegetables, and trees since childhood. While I no longer live on a farm today, I still enjoy spending time on my garden and sharing my knowledge with friends and fellow garden enthusiasts.