Article by Tricia Christopher, Landscape Architect and Designer of the Mediterranean and Sensory Gardens

Weeds…. they can be overwhelming this time of year due to spring rains and warming weather. Don’t despair! You can win the battle of the weeds without resorting to deadly chemicals or furious digging and yanking. A weed-fighting method called “sheet mulching” works in harmony with nature; weeds disappear while soil improves at the same time.

How does it work? The weeds are literally smothered and not allowed to see the light of day. Layers of compostable materials (such as newspaper or cardboard, compost and wood chips) are piled on top of the weeds. Then the naturally occurring microorganisms and worms in the soil below do the magical job decomposing the weeds.

With time, the mulch layers break down and provide organic material and nutrients to the soil. Thus, sheet mulching not only gets rid of weeds, it also improves the soil fertility and helps a happy community of earthworms keep the soil aerated.

In contrast, digging out weeds disrupts the soil’s natural ecosystem and destroys earthworm tunnels. Spraying with herbicides adds environmentally questionable chemicals to the garden. Sheet mulching works with nature rather than against it. 

Sheet mulching is simple and inexpensive, just follow the steps below:

1. Dampen whole sections of newspaper or flattened cardboard boxes by placing in a large bucket or play pool filled with water. Remove and place directly on weeds, overlapping for complete coverage. Another alternative is to use cardboard sold in rolls, using at least 2 to 3 layers; spray cardboard with water to dampen after rolling out.
2. Spread a  4” to 6” layer of mulch over the newspaper/cardboard.  The mulch can consist of wood chips or a combination of weed-free compost and wood chips. Wood chips can often be found for free from a local tree company.
3. Plant new plants by cutting holes through the newspaper/cardboard.  Replace mulch around plants, but don’t smother them! Hold the mulch a couple of inches away from the base of the plant. If large plants are being used (such as 5 gallon cans and larger), it is best to plant them first, and then sheet mulch around them. Try to keep soil under the sheet mulching so weed seeds will be smothered.
4. The weeds will naturally bio-degrade within a month or two. The wood chips or compost can be replenished annually as needed. Subsequent weeding is much easier as the soil becomes looser and more organic.The sheet mulching technique was used in both the Mediterranean Garden and the Sensory Garden in The Gardens at Lake Merritt with great success:

   

    Before Sheet Mulching: Dense weeds covered the Mediterranean Garden site.

    

    Dampened cardboard was placed in layers over the planting beds.

   Drip irrigation tubing was installed on top of the cardboard.

    

   

   Compost and wood chips were placed over newspaper layers at the Sensory Garden.

    Holes were dug through the layers for new plants.

    

   The completed Mediterranean Garden 1-1/2 years later.Weeds are still suppressed by sheet mulching and the plants are flourishing

   You’ll find Tricia Christopher in the Mediterranean Garden most work party days (the first and third Saturdays of every month). She’s happy to answer your questions about Mediterranean gardening and/or visit her website http://www.tchristopher.com/