The best thing to know about what to put down before mulch is that compost and cardboard work far better than landscape fabric. A thin layer of finished compost feeds your soil while cardboard blocks weeds without the problems that plastic barriers create. Your prep work matters more than the mulch itself for long term success in any garden bed.
I struggled with a weed-filled bed near my back fence for three years before getting the method right. Grass kept pushing through my mulch no matter how thick I spread it around my plants each spring. Then I tried the cardboard method and watched those weeds die within weeks of laying it down. The cardboard smothered them while breaking down into the soil over time. That bed has stayed clean ever since with just annual mulch top-ups.
Your prep before mulching should start with pulling any existing weeds by hand or cutting them low to the ground. Next spread cardboard or newspaper over the whole bed surface. Overlap the edges by several inches so weeds cannot sneak through any gaps between pieces. Wet the cardboard down so it stays in place while you work on the rest of the bed prep.
Compost does two jobs at once in this layered system that benefits your plants. It feeds your soil biology by adding organic matter that worms and microbes need to thrive all season long. It also gives your plant roots something rich to grow into as they spread out from the stems. NC Extension says to spread one to two inches of finished compost over the cardboard. Then add your mulch on top of that layer.
The weed barrier under mulch question trips up many gardeners who reach for landscape fabric first. I did the same thing years ago and regretted it within two seasons of installing it. That fabric blocks earthworms from grabbing fallen leaves and pulling them into the soil. It stops compost from mixing in over time. SDSU research shows fabric beds lose their soil health faster than natural ground does.
Cardboard breaks down within a season or two and becomes part of your soil instead of sitting there forever. Worms love eating the cardboard fibers and the glue used on most boxes causes no harm to your garden at all. Newspaper works too if you use eight to ten sheets thick in each layer. Just avoid the glossy inserts since they take longer to decompose and may leave residue behind in the soil.
For heavy weed problems, you can add an extra step to your prep before mulching process. Cut the weeds down first, then wet the area well with a hose or wait for rain. Lay your cardboard over the wet ground so it sticks down flat against the surface. Add compost on top of that and then your mulch last of all. This triple layer smothers even the toughest grass and dandelion roots in your beds.
Skip the landscape fabric in almost every situation you face in your garden beds at home. It costs more than cardboard and works worse over the years as debris builds up. Weeds grow on top of the fabric in the mulch layer and root right through the mesh anyway. You end up with a matted mess that traps debris and stops water from soaking in where your plants need it most.
The right prep takes a bit more work upfront but saves you hours of weeding each season after that first year passes. Spend one afternoon layering cardboard, compost, and mulch in the proper order for best results. Your beds will stay cleaner and your plants will grow stronger from the rich soil you create beneath them. That initial effort pays you back for years to come with less work and healthier plants overall.
Read the full article: Mulching Flower Beds: Complete Guide for 2025
