- Author: Paula Pashby
UC Cooperative Extension County Master Gardeners (Solano & Yolo) are currently renovating the 900 square foot Willis Linn Jepson Native Plant Garden at the Peña Adobe in Vacaville. We have been working in many phases, involving clearing weeds out and preparing the space and soil for adding new plants. The most recent phase consisted of ‘sheet mulching' the area using cardboard.
According to the University of California Agriculture & Natural Resources (UCIPM), ‘sheet mulching with cardboard or the heavy paper is sometimes applied as mulch and can be inexpensive and relatively easy to apply. Sheet mulching can decrease weed growth until a newly planted ground cover fills in open spaces and grows enough to shade or crowd out weeds.'
Along with reducing weed growth in the garden, cardboard has many other advantages, such as adding organic matter to the soil when it decomposes, improving the garden's drainage, and boosting nutrient levels. Also, earthworms are very attracted to the cardboard and are great for the garden, since their movement through soil increases aeration, nutrient cycling, and water infusion. The earthworm ‘castings' manure (worm poop) provides an organic type of fertilizer that offers many beneficial nutrients for plants.
To get the garden ready for the cardboard sheet mulch at the Peña garden, we removed the weeds as much as possible. If the soil is in poor condition, there is abundant literature that includes the advice of adding healthy compost, like horse manure, prior to installing the cardboard. It was not necessary to add the manure since the soil is already in good condition.
With the help of veteran Master Gardeners, we took the following steps to install the cardboard sheet mulching. We did encounter some ‘lessons learned' on the job, so I am also including some handy “do's and don'ts” to the list:
- Get large pieces of cardboard! As you can see in the pictures, we did use some small boxes that took longer to position than it would have if we used larger cardboard pieces. We had a donation of many smaller home delivery boxes and made the best with what we had, even though it took the extra time to install.
- Cut the cardboard along the seam and unfold it into one large piece.
- Try to remove tape and labels, if possible, but any remnants can be later removed when the cardboard decomposes in the garden.
- Hose down the garden area with the cardboard to help with the decomposition process.
- We will be adding a top layer of mulch in a few weeks, so for the interim, we needed to secure the cardboard to the ground with 8” garden stakes, pounding them in with rubber mallets. We used the 8” stakes because sometimes the smaller stakes do not penetrate the ground enough to hold the cardboard in place.
- Don't hammer the stakes in too hard! We found that if we hammered the stakes in too deep, they would just break through the cardboard.
- The stakes can easily bend, so hold the stake at the bottom when pounding to reduce the chance of bending.
- Sometimes you will be dealing with large roots or extremely hard soil, making it difficult to pound in the stakes. If the soil is hard, soak the area prior to putting the cardboard down. If the stake won't go all the way in because of roots, don't fret too much - they usually still stay in place if you get the stakes partially into the ground.
- Start from one end of the garden to the other and avoid stepping on the cardboard and risking damage to the cover, since we discovered that it was easy to create holes in the cardboard.
- Overlap the cardboard pieces by 6 to 8 inches and make sure to cover the cardboard flaps. We initially did not overlap and cover holes as much as we should have, mostly because we were running out of cardboard. A few weeks later we discovered weeds and grass gingerly growing through the tiniest holes and gaps in the cardboard, lesson learned! So, we pulled the weeds and grass out and put more cardboard down, overlapping as much as we could.
We probably used more stakes than necessary, but I think it all worked out well. A couple of days after we installed the cardboard, we had a few days of extremely high winds in the area. I had panicked visions of cardboard flying all over the Pena Adobe area and onto the freeway. The next day we went to the site and checked on our project and happily discovered that all the cardboard was secured solidly in place, hurrah!
The next steps for this beautiful garden are to add a few inches of wood chips, install the plants, set up the remaining irrigation system and create the necessary signage for the new plants. I can already visualize how the garden will look like this coming spring and am excited to continue working with my fellow Master Gardeners to make this vision a reality.
If you would like to visit the garden, take the Pena Adobe exit off I-80 West. Cross back over the freeway and turn left into the park. Take an immediate left to enter the Pena Adobe. Parking in the Pena Adobe parking lot is free (there is Insert Imagea parking fee within the main Lagoon Valley Park).
Here is a great link from UC Davis Arboretum and Public Garden on sheet mulching with cardboard: https://arboretum.ucdavis.edu/news/break-up-with-your-lawn-using-cardboard
See next page for another picture: