Another Look at Lasagna Mulchingcomments (4) October 18th, 2016
Some gardeners swear by the lasagna mulching method for making quick work of building rich garden soil. Instead of tilling the garden bed, lasagna mulching uses layers of cardboard topped with newspaper, leaves, straw, grass clippings, kitchen waste and manure to increase organic matter in the soil.
However, it turns out science doesn't support this method for creating a healthy nutrient-rich soil, according to Dr. Linda Chalker-Scott with the Puyallup Research and Extension Center at Washington State University.
Dr. Chalker-Scott, author of How Plants Work and The Informed Gardener Blooms Again, spends a good deal of her time conducting research to evaluate landscape practices and dispel common gardening myths.
One of those myths has to do with lasagna mulching. As great as it sounds for vegetable gardeners who'd like to build rich soil without digging or tilling, sheet mulching isn't the answer.
Layers of sheet mulch reduce water and air availability to plant roots, she explains. Because the layers are impermeable, it's not that great for the soil underneath.
"Overuse of any nutrient can create soil, plant and water problems," she adds. Too much lasagna can actually be toxic.
Gardeners often try to counter her claims by explaining how many earthworms they find in their lasagna garden soil.
That sounds like a good argument, but the reasons worms move to the surface is because they can't breathe under the layers.
Instead of falling for the appeal of a quick method for building healthy soil, she recommends a science-based alternative of using coarse woody mulches instead. Over time, woody mulches can help increase the percentage of organic matter in the soil to reach the 5-10% ideal.
Woody mulches also control weeds, add nutrients slowly, and allow for water and oxygen movement.
Thick layers of woody mulches are a good alternative to using glyphosate to kill lawns or weeds to make way for a new garden, too. Mow the area to the ground while it's dormant, cover with 12 inches of wood chips and then let it cook. When the plants are dead, gardeners can move the mulch to prepare for planting.
To read more horticultural myths and learn about their science-based alternatives, visit Chalker-Scott's WSU Extension website.
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