How to Fertilize Mulched-Over Plants

Mulched plants and flower beds are beautiful. But how do you fertilize them?

I have a beautiful flowerbed that is covered with wood chip mulch to suppress weeds. It took a long time and physical labor to lay down all the mulch. When it’s time to fertilize my flowers, I’m always curious if it’s okay to fertilize on top of the mulch.

If you’ve had the same question, let’s work together to find an answer!

Can You Put Fertilizer on Top of Mulch?

In general, you can put fertilizer over mulch. However, depending on the type of fertilizer and mulch you are using, it may be better to remove the mulch. 

Fast-Decomposing vs. Slow-Decomposing Mulches

If you have a fast-decomposing mulch, you can apply fertilizer over the top of the remaining mulch. Mulches that fall under this category include seed hulls, grass clippings, and leaf mulch. By the time you are adding your fertilizer, most of last year’s mulch will have decomposed.

If you have slow-decomposing mulch, traditional and bark mulches included, it is best to rake it aside before applying fertilizer. You want the fertilizer to have as much contact with the soil as possible so that the nutrients can reach the plants’ roots. Slow-decomposing mulches may prevent nutrients getting absorbed into the ground.

Fallen and dried leaves used as a garden mulch and fertilizer

Granular vs. Liquid Fertilizers

If you are using a granular fertilizer, it’s always best to have as much ground contact as possible. Granular fertilizers work optimally when they are in contact with a moist substance. They are formulated to work with soil, which increases the amount of surface area that it is in contact with, allowing it to break down and release nutrients.

If you use a liquid fertilizer, it is okay to fertilize over the mulch. The liquid fertilizer will work its way down through the mulch to the soil beneath.

A person watering a dried and black wood

How to Fertilize Over Mulch

To fertilize over mulch, we will simply use the aforementioned principles as a guide.

In gardens where less than ½ inch of mulch remains or where there is fast-decomposing mulch, apply a layer of granular or liquid fertilizer, then a layer of new mulch. Cover the area with at least 2 to 3 inches of new mulch to prevent future weed growth.

In gardens and areas where a significant quantity of slow-decomposing mulch remains, avoid using granular fertilizer. Instead, apply a liquid fertilizer so that the nutrients can make their way into the soil.

Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
More ArticlesGeneral Guides